Why shouldn’t everyone use Evan’s NPG+ coolant?
 

I don’t want to start an argument about the best coolant. I simply want to explain why I think there is no good choice in coolant compared to Evan’s NPG+. It is completely different from traditional antifreeze, and I’m seeing nothing but benefits from the literature. I know this is a general concept, but I drive a 3rd Gen, and I’m most interested in comments from other 3rd Gen owners.

I just ordered some Evan’s NPG+ coolant after deciding to switch to it rather than a traditional antifreeze/water mix. With Evan’s NPG+ you do not add water to the coolant, it’s all coolant.

I started thinking about overheating and the components of the cooling system and how using Evan’s NPG+ would effect them. Here are my thoughts organized by topic.

Warning: This is long (almost 1,500 words…). And I hope it seems well thought out.

Footnotes are at the bottom with links, and are denoted by parentheses and numbers (like this (1)).

Traditional Overheating

Traditional overheating occurs when the coolant starts to boil. This will usually result in a failure of the cooling system due to pressure followed very quickly by a loss of coolant and quickly rising engine temperatures. Think about it, once pressure is lost, all of the coolant will begin to boil very quickly (the pressure inflated the boiling temp, once the pressure is released everything will boil, and fast). The boiling only serves to worsen the problem since expansion will force the coolant out of the car faster, and once air replaces the coolant in the coolant lines, it’s all over. Engine temperatures rise quickly and metal starts to warp.

Evan’s NPG+ coolant doesn’t boil until 375 degrees F. As an example, Peak Antifreeze at a 50/50 mix will boil at 265 degrees F (1).

So, inherently, Evan’s NPG+ is much less likely to cause overheating due to boiling. If it does, your engine is already running really, really hot.

Thermostat

The thermostat allows the engine to heat up more quickly, and it is designed to try and keep the engines operating temperature above a specific level. When the engine is above this level combustion is more complete and there is less wear on the engine. It is generally accepted that temperatures around 200 degrees F are good (2)

Obviously in a cooler climate the thermostat plays and important role as it can open and close once the engine is warmed up to keep the engine at a certain level. The thermostat has nothing to do with overheating; it simply helps to keep the engine above a certain temperature by closing when the coolant temp drops too much.

Now, Evan’s NPG+ is supposed to be very efficient at heat transfer. That means it heats up and cools down faster than water or water/antifreeze. That means your car will warm up faster with Evan’s. Your temps will also return to normal faster after hard driving.

Now, if I live in a warm climate, do I need a thermostat? I ask because I am trying to bulletproof the coolant system, and removing parts from the cooling system removes the chance that those parts will fail. You certainly don’t want your thermostat failing and sticking shut, that would cause overheating regardless of the coolant you are using as without access to the radiator the coolant can’t effectively release heat.

AST (Air Separation Tank)

I’m one that believes the AST should be left on the vehicle since it was engineered into the vehicle. Your coolant system isn’t a vacuum (it’s just the opposite), so you cannot get 100% of the air out. The AST helps release air from the system. Air in your cooling system can still cause hotspots, which can contribute to failure regardless of the coolant being used.

Obviously you should be using an after-market AST.

Corrosion and Scaling

Anytime you have water and corrodible metals, corrosion will occur. Antifreeze contains corrosion inhibitors to reduce or eliminate corrosion in the coolant system. Corrosion can reduce the efficiency of your cooling system and contribute to failures.

Scaling is caused by what’s in our water. Take a couple cups of tap water and boil it off. What’s left is scale. Scaling can clog the fins of our radiators and make them less efficient.

Evan’s NPG+ has no water and will not corrode or cause scaling.

Pressure

Our coolant systems are pressurized to increase the boiling point of the coolant. With Evan’s NPG+, the boiling temperature is already very high, so we shouldn’t need as much pressure to maintain efficient cooling.

Evan’s says that you can run a low-pressure (7psi) or no-pressure (0psi) cooling system using NPG+ (3). This will reduce general stress on the system (lower pressure equals less stress) and reduce leakage.

Overheating can cause intense pressure as the coolant starts to boil. This can cause a failure in the cooling system; causing a loss of pressure and fluid. If you run Evan’s NPG+ in a 0psi cooling system, you remove the risk of an overheating pressure release (which quickly drains the coolant) since there is no pressure to begin with. You will still have fluid entering your overflow reservoir though, since NPG+ still expands when it’s heated.

Coolant Temperatures

The more energy the coolant can absorb, the higher the coolant temperatures will be. There’s no shortage of heat as the combustion chamber can get very hot (can reach 4,500 degrees F (4)).

People have reported higher coolant temperatures using Evan’s NPG+ (5). This is because it’s more efficient. Of course, you should expect it to be higher coming out of the engine, and conversely, you should expect it to be lower coming out of the radiator (compared to water/antifreeze).

Now, coolant temperatures by themselves aren’t an indication of situations where heat causes engine damage. We watch our water temperatures closely to avoid an overheating situation where the coolant boils.

My Questions

1. Safe Engine Operating Temperatures

Cars overheat because the cooling system can’t remove enough heat. Evan’s NPG+ allows the cooling system to continue functioning at much higher temperatures than traditional antifreeze.

My question is: How high of an operating temperature would cause engine damage? Assuming you stay below the boiling point of Evan’s NPG how hot could you safely run your engine in terms of oil and coolant temperatures? At what temperature does a high-grade synthetic oil such as Redline break down?

2. Impact of a no-pressure cooling system

In a no-pressure cooling system you will have less stress on the system as a whole and less change of leakage.

Are there other factors that I am not familiar with which would make a low-pressure cooling system more desirable than a no-pressure cooling system? If you are using Evan’s NPG+, what pressure level are you running your system at and why?

3. Thermostat: Should it stay or should it go now?

I live in a warm climate (Phoenix, AZ). In the winter I might see freezing a couple of times, certainly nothing lower than 30 degrees F, and even then it will get into the 50s/60s in the afternoon on those “cold” days.

Do I need a thermostat? The real question comes down to this. At what external temperature does a freely flowing coolant system (open or no thermostat) in an RX7 cause the temperature of the coolant to go below a certain threshold (say 190 degrees F)? Now, this question is complicated by driving style (drive hard, it gets hotter), and speed (drive fast and you get cooler much faster). I’m thinking I will just leave the thermostat on just in case for during colder weather.

Conclusions and Follow-up

I don’t see any reason not to run Evan’s NPG+ as a coolant. As well, I don’t see any reason not to run Evan’s on a no-pressure cooling system. I only see reasons TO do this.

Now, I’m not using Evan’s NPG+ coolant right now. Why? Because I just ordered it this morning. Once I get it I will be flushing my system, replacing my stock AST, replacing the thermostat (with a new Mazda one), and filling up with Evan’s. Hopefully I will have my water temperature gauge installed by this time, but I’m not sure if I will. And I’m not really concerned about specific water temperature readings, I’m more concerned with water temperature levels when they deviate from what I’m used to seeing (might indicate a problem).

Besides this, I’m going to do some testing of the thermal characteristics of Evan’s NPG+, water, and water/antifreeze mixes. Specifically, I’m going to test:
1. Energy absorption rates (using a fixed energy source and a fixed amount of fluid, how fast will the fluid temperatures rise to a specific point).
2. Energy release rates (same thing as 1, except I will be timing the cool down period from a hot temperature to a lower temp).

I will post back as soon as I’ve had a chance to do these tests. I’m not going to be super-scientific; it’s going to be kitchen chemistry. But it should be controlled enough to produce valid results.

Footnotes:
1. Pep Boys website, Peak product information : [url]http://www.pepboys.com/products/peakantifreeze.shtm[url]
2. HowStuffWorks.com engine cooling system information: http://www.howstuffworks.com/cooling-system1.htm
3. Evan’s Cooling Systems NPG+ information page: https://www.evanscooling.com/main31.htm
4. HowStuffWorks.com engine cooling system information: http://www.howstuffworks.com/cooling-system5.htm
5. RX7Club.com Forum Thread: https://www.rx7club.com/forum/showth...hlight=evan%2A

Good research, good essay, nice job. Well, unfortunately i'm not here to post about my experience, but to second that I haven't been able to find any reason not to use NPG+ in an FD...

its supposed to run cooler and not foam (although im sure these are not all the benefits)..i heard of a guy running evans in his FD with stock radiator ran same temps as a guys with a fluidyne not sure what the exact numbers were but it was over 100 degrees that day. ive heard its the best you can get and like optusX4 said why would you not use it..

Damn - that's a Doctoral Thesis on FD3S cooling! I can appreciate the thought that went into it.

But .......I have to add my .02 cents, and living in Tucson (OK, it's usually 5 degrees cooler than Phoenix) I think I can speak from experience.........

What is wrong with distilled water and Red Line Water Wetter? Lowers the boling point significantly, lubes the water pump, inhibits corrosion and best of all is damn cheap! ($20 total and I use 2 bottles of Water Wetter just for fun.)

Works for me for the past five years.......never an overheating issue even when I'm on the boost hard. I am quite frankly impressed by how well the stock cooling system works IF (and that's a BIG IF) everything is functioning properly.

I thing the Evans makes sense if you are running boost levels more than 20% over stock or have a FMIC. I just can't justify the expense otherwise - rather put it into a good SMC intercooler and better airflow through the enging bay ala my "hot air out" ghetto duct mod.

Stay cool!:cool:

I am not an expert on Evans coolant, but you might want to check that fact. From what I have heard (not experienced) Evans coolant is actually much worse than water/glycol mix at heat transfer. It does have a higher boiling point, but that doesn't mean that the engine isn't getting hotter than normal. Distilled water alone is the most efficient at heat transfer, but running water only in your engine will result in a radiator and cooling system full of rust flakes in short order. (Did you catch that Ron?) I think we all know what that will eventually do to your engine. Antifreeze has sacrificial metal in it to act in the oxidation reaction that takes place inside the engine. Without coolant, the metal in your engine is part of the reaction!

People are getting higher coolant temperatures because it is LESS efficient, not "more efficient." I think that coolant temps comming out of the radiator are HIGHER too! Otherwise, the eigine would be running cooler, not hotter. Think about it. The system has to reach a steady state at some point in which the heat in is the same as the heat out. If the temps are higher (before or after the radiator does not matter) then the system has be run hotter in order to release the same amount of HEAT. In other words, heat transfer is LESS efficient than water/antifreeze.

I have not personally done any laboratory testing on this matter, so I ecourage you to carry out your experiements on the Evans coolant and post your findings. I would love to see the results.

Jeff

Hey, a Rex-7, my brother lives in Jacksonville!

Anyway, Water Wetter contains anti-corrosion inhibitors and lubricants. Go to www.redlineoil.com for the details.
Five years, 30K miles, and everything is whistle clean inside the coolant passages, although I do change coolant every year regardless of mileage. Original water pump at 75K on my '93.

I think you'll find that most competent rotary mechanics (and racers) agree that it is the way to go......I am not an expert rotary mechanic but I have rebuilt several dozen airplane, motorcycle and car engines. I am an FAA certified repairman and see all kinds of "miracle" coolants, teflon supplements, oil "boosters", octane enhancers, yadda yadda yadda. It's ALL marketing hype.

I just flushed and put in Evans today. I have been having some cooling issues (running up to 215-218 in bumber to bumber in 100 degree temps) and also replaced the thermostat as recommended by RP. These temps were while I was doing all I could NOT to get into the RPMs and bring temp higher.

After, it was pegged at just under 200 in same 100 degree weather (bumber to bumber traffic). I also worked the car very hard for a few mins to see if I could get the temps to rise. Got it to 215, but it took some work....and it dropped back to 200 pretty quickly.

I think I may have been having a thermostat problem as well, so my previous temps were a little inflated over normal. But, I feel much better knowing that I won't have localized boiling in my coolant when I hit 220+.

Tomorrow will be the test though, as we are having an RX7 road track day, and ambient temps will be close to 100 again. I have read that some cars on the track with Evans have run into the 250-260 range which Evans says is on the "high normal" range under hard conditions. Not sure I can handle seeming my temp gauge get those numbers, but we shall see.

I'll post again if I blow my engine!

I run Evans and find my temps very comparable to my old mix of 75/25 water/coolant with water wetter when driving around town and even during mildly aggressive driving. Really aggressive driving will drive the temps higher than my old mix. This makes sense as Evans is a poorer heat transfer medium, Evans entering the radiator will need to be at a higher temp than water/coolant to transfer the same amount of heat with same waterpump flowrates and same ambient air temp day.

However, having a zero pressure system that absolutely will not boil over eases my concern of failing a hose or belching out coolant through the overflow which is a quick way to lose a motor. No local boiling of Evans in the motor which should significantly reduce hot spot temps makes me feel better as well; no data to evidence this but its a good selling point for Evans.

As for the tstat, I suggest drilling 3 to 4 large holes around your tstat valve as this is what most of the track guys do, works well and will help warm the engine up as compared to no tstat. I see no advantage of running an AST and have run without one for years, first water/coolant and now Evans (fewer connections, fewer hoses, and fewer opportunities for coolant leaks).

OVERHEATING:

Yes, I agree with you on this.

THERMOSTAT:

No. I disagree with not running thermostat. The thermostat is a restrictor, i.e. it causes a pressure drop and reduces flow. Without the thermostat, coolant doesn't spend enough time for sufficient heat (i.e. energy) transfer. So the thermostat is designed to work with water and anti-freeze. However, NPG requires greater flow rate because it's I think 10 times more viscous. The way to do it is to drill a few 1/4" holes around the perimeter of the thermostat to increase the flow rate.

AST KEEP OR DELETE?

I haven't installed NPG yet but here are my thoughts.

THERMOSTAT:

No. I disagree with not running thermostat. The thermostat is a restrictor, i.e. it causes a pressure drop and reduces flow in the engine. Without the thermostat, coolant doesn't spend enough time for sufficient heat (i.e. energy) transfer.

Our thermostat is designed to work with water and anti-freeze. However, NPG requires greater flow rate because it's I think 10 times more viscous. The way to do it is to drill a few 1/4" holes around the perimeter of the thermostat to increase the flow rate.

AST KEEP OR DELETE?

Definitely keep. Remember, we don't have a labyrinth seal between the rotor housing and the side housing. We have only a single o-ring on one side of the coolant passage and another o-ring on the other side. Therefore, during cold start, you're going to have air/combustion gas leak into the cooling system. With air pockets in the engine, you'll get localized warping of the housing, especially on the top part of the block due to air pockets being trapped there.

Not only do I think the AST is necessary, I think Mazda engineers done screwed this one up. They should have ran a coolant expansion bottle like BMW/Mercedes/Volvo and some Toyotas. In fact, once I switch over to NPG with my new reman, I'm running a Toyota expansion tank with 5-7 lbs. cap.

CORROSION AND SCALING

I think you'll still have corrosion due to combustion leaks into the cooling passage. However, it will be minor compared to water/coolant corrosion.

ENGINE TEMPERATURE

I am quite sure that an engine can run fine at 250 deg. F. Several limiting factors: 1. thermal expansion of the material of the engine, 2. oil, which breaks down starting at 250 F for conventional oil. 3. polymeric seals in the system.

There was a post by a forum member here in S.Calif who says he saw 260 on the track but not on the street. I also plan to run two large oil coolers from CWR, which should help drop coolant temp as 1/3 of the heat of the rotary is carried away by the oil.

Ron, Water wetter eats the coolant seals...Don't use it.

Here is another good thread that I read awhile back

https://www.rx7club.com/forum/showth...=evans+coolant

Facts:

Evans coolant is LESS EFFICIENT at heat transfer than water/antifreeze mixture.

Evans has a lower heat capacity.
Evans is worse at conducting heat.

This means Evans will have to run hotter to transfer the same amount of heat as standard water/antifreeze.

The advantage to Evans is that it won't boil until much higher temps, this keeps the heat dumping into the coolant and prevents hot spots. Once conventional coolant gets hot and boils the engine temp will spike as noted in the first post.

Pomanferrari:

The coolant doesn't need to spend more time in the engine to pick up heat. Imagine running water slowly over hot metal vs. quickly. Will a firehouse cool down a hot engine or do you need to just put a trickle of water from a hose so it can spend more time in the engine?

I like the results I get using Evans.

I see temps ranging from cold as possible 180 (freway cruising in 70 deg weather) to 250+ (track use in 100+ deg weather).

Evans coolant temps are very close to what you would see with water mixtures. Therefore, the benifits of no localized boiling, low preaaure and zero corrosion outweigh the slight increase in coolant temps (if there really are any).

5-10 degrees of increased coolant temp won't make much difference to your engine unless it's the last 5-10 degrees that takes your coolant to its boiling point.

That does not mean I would run my engine at 375 degrees since thats a 150 degree increase above normal operating temps. However 245 instead of 235 under very very hard driving is hardly worth mentioning. Do you think your engine cares only about the slight difference in coolant temp or about the fact that water based coolant is already starting to boil?

If you are sure that your coolant will never get that hot and/or that you will not loose coolant system pressure then water based coolant is probably all you need. Below those temps any slight differances in temp between Evans and water based coolants are academic. However above 212 @ 0 psi we know Evans wins and water w/ water wetter is toast.


http://www.e30m3performance.com/myth...ter_wetter.htm

http://www.amug.org/~tristar/text2.htm

twokrx7 covered it well.

NPG+ allows you to go beyond where Water systems will reach unstable local boiling, usually means hot roadtrack events, fmics driven hard in hot weather, or just mega power used often. But u go there at very high bulk temps, and minor glycol boiling. Pinapple racing was had good experience with it.

But evans is inferior in general heat exchange. coolant gets warm quickly, but sucking up less heat in the process. Higher metal temps cause the oil temps to rise too.

Less advantage for normal driving, just long coolant life and low/no pressure. Best to keep an ast for zero psi use. Adding restrictor pill in the port to filler neck will assure the pump inlet does not draw a vacuum and collapse the lower hose.

What i see with this evans or not discussion is basically "how hot will your coolant get" IT seems if you run under 212F then regular coolant seems fine.

I have a question for those that run regalar water based coolant on the track, "what was the max temp you saw on the coolant"

And running evans almsot means you should/must run synthetic oil under hard driving.

Another question. Why EXACTLY is redline water wetter bad, as well as the "extended life" coolants? I've seen this thrown around, but no explanation.

Danny

Yeah, I've heard that, but I would need to see some evidence to back it up. Mine went well before I started using water wetter, but Copper Block Weld cured that problem. I know I'm living on borrowed time.........:(

Turbo Jeff, obviously you aren't familiar with several theories of heat transfer.

Rather than arguing with you on this point with crap load of material from my college course on Fundamentals of Heat and Mass Transfer, I dare you to run without a thermostat for one week and report back to this list.

If you take me up on this dare, let me tell you what will happen: your car will over heat, period.

heat transfer=mass flow rate*cp(delta T), is that the fundamentals of heat transfer that your referring too?

Poman I tried to be polite, you should try and do so also.

Your wrong about the coolant flowing to fast to pick up heat from the engine. Plain and simple. The cooler the coolant is the quicker it will pick up heat from the hot engine. Coolant moving SLOWER will cause LESS heat to be aborbed since delta T will become smaller.

Removing the thermostat may cause the engine to overheat, but not due to the coolant flowing past the hot engine parts too fast.

Educate me on how heat transfer works in WA DC.


Jeff

I totally agree with turbojeff on this one. I've had thermodynamics courses too... flowing at a faster flow rate will increase the turbulence in the system, which increases cooling efficiency. But not only that, as turbojeff stated, heat transfer is a function of the difference in temperatures of the two mediums. A higher delta T will result in greater heat transfer. Sooo... if you're running coolant through the engine faster, it will be colder AND the flow will be more turbulent, so cooling efficiency will increase.

Honestly, I think as far as heat transfer efficiency, I don't think it will make a significant difference whether or not you run a thermostat (I'm just using my engineering judgement here).

If I'm wrong on any of these points, please explain.

Re: Why shouldn’t everyone use Evan’s NPG+ coolant?
 

...because of coolant sludge (oil/ carbons/ etc.) that necessitate annual coolant flushing.

The only problem I see with a high flow rate of coolant is that maybe the coolant will not be sufficiently cooled by the radiator if it does not spend enough time there. The engine may or may not overheat with the thermostat removed, depending on the efficiency of the radiator, the flow rate of the coolant, ambient temperature, and the capacity of the cooling system. I've taken thermostats out of vehicles before with no problems, and on the one with a temp gauge, it sat at 170. This was with a 4 core radiator, however.

I don't get it.

Are you saying that removing the thermostat may cause overheating?

Ed

My apology if my statement came off rude. I designed a cooling tower for my senior year project and we found that assuming that all other parameters are the same, moving coolant too fast didn't help. The best thing for a system with all other things constant is to eliminate boundary layer flow or increase turbulence.

Hell, it's been 12 years ...

Not sure about your formula as it is ok for just one side of the system, but you've got other things going on on the radiator side.

Hey but theory is theory is theory, test it by removing the thermostat and see for yourself.

EXACTAMUNDO. Especially with the RX7 high volume pump.

One other thing turbo jeff, the politicians and lawyers inside the belt way here in the center of the known universe are causing a singularity to be generated spontaneously so physics and quantum theory are not the same here as elsewhere in the known universe. But you already know that....

You're right on the word "may be." I would qualify that as "usually" especially if you're running a stock radiator. Don't ask me how I know that the FD will over heat w/o a thermostat.

I'll tell you anyway. My t-stat wouldn't close in cold mode when I inspected it. The dealer was 15 miles away. I cut the core out to make sure it doesn't shut tight either and went to the dealer. Note that I left the round section in just so there will be some restriction- Cruising in 95+ F at highway speed and AC on. The car overheated within 15 miles.

And you can increase turbulence by increasing flow rate, and you can increase flow rate by reducing restriction (i.e. removing the t-stat). Basically, at slow flow rates, a fluid will flow in layers (laminar flow). As you increase flow rate (or decrease the size of the flow channel, or decrease the fluid's viscosity), the flow becomes turbulent. Turbulent flow is necessary for good cooling. I don't see how removing the t-stat could make an engine overheat... it makes no sense at all. Reducing flow restrictions will always improve cooling, all other things kept constant.

I'm really not trying to argue with you, but I can't come up with a reason why *restricting* a cooling channel will improve cooling.

BTW: I'm don't think removing the T-stat is a good idea. The flow restriction caused by it is probably negligible anyway, and if you're good with maintenance, it shouldn't go bad. I don't know if they're available for the FD or not, but I remember seeing t-stats that were designed so that if they ever failed, they would fail in the 'open' mode so your engine won't overheat.

Paw 140.

Not arguing here but for FDs, they'll over heat if you remove the t-stat. My 1970 Olds Cutlass never did running w/o a t-stat but then the cooling system was overbuilt.

Like I said, you got to look at the whole system, not just the heat transfer b/w coolant and engine on the engine side. But what do I know? I'm just a wordsmith.

Did you wonder why Evans suggest removing the t-stat on GM vehicles but Pineapple doesn't recommend doing that on FD?

OK, no flames just technicalities:).

What I was correcting, and what started this whole thing is that the coolant doesn't need to "slow down" so that it can absorb more heat.

I agree with you that the engine can/will overheat without the T-stat but that isn't due to the coolant moving to fast. Wrong theory, correct result.

On your cooling tower, notice you didn't say moving the coolant to fast didn't cause it to transfer less energy, it just didn't transfer more. Totally reasonable, maybe the other side of the equation was unable to transfer heat into the coolant any faster.

What I'm trying to do is help correct the mis-statement that the coolant isn't moving to fast to pick up the heat. Really doesn't make much difference but maybe someone will get some wild idea to slow it down more with a restrictor or something and cause even more problems...

BTW, my senior project was permanently installing a turbo diesel engine on a engine dyno and fully instrumenting it (temps, pressures and flowrates of everything) and logger everything with a datalogger. The engine could not hold steady state max rated hp without overheating the oil (235F +). We had a flat plate heat exchanger cooled by city water (58F) for engine oil, oil came into the cooler at 235F and exited at 85F. It would have helped to have a higher capacity oil pump to get the oil in and out of the cooler faster...

Jeff

Took the car on a road track yesterday with Evans for the first time. I was very pleased with the results. Temps were close to 100 and we did 5 20 min sessions.

The first 2 sessions I actually ran with the windows up and AC on. Temps reached 230 peak. But nothing to worry about with Evans.

The last 3 were all out with AC off and my temps peaked at 222. I was driving very hard under some fairly extreme conditions the full 20 mins. I am very pleased with these results.

Here are my reasons for using Evans:

1. Zero pressure, much less chance for failure. You really lower you chance of failure down to T-stat and water pump. With little to no stress on the hoses/clamps chances are you won't blow them.

2. Very high boiling point. Many benifits here. No localized boiling, no loss of coolant due to boil over, and less stress on system. Once temps get into the 220s+ with regular water mixes, cooling effeciency drops dramaticly as temps rise making the situation detrimental very fast.

3. Less corrosion. Not that big of a deal in my book. Just flush regularly.

Reasons for not using Evans:

1. Cost. At $22 or so a gallon, it aint that cheap. Need about 3.5 gallons for my FD with Koyo rad. I still think I will end up flushing once a year because we all know that a rotary cooling system gets contaminated.

2. If you need to add coolant, you can't just put water in! Better have some Evans around just in case.

Not in my FD yet...but in my motorcycle..
 

I haven't tried NPG (or NPG+) in my FD yet, but I have tried it in my 2001 Yamaha YZF-R6. And let me tell you...it scared the crap out of me. Why? My cooling system ran a lot hotter...and my fans would activate late and shut off way too early. The temperatures would just keep climbing if I was idling. I have since changed to distilled water and water wetter since I have to take this bike to the track. Here are the temps I was running:

2001 Yamaha YZF-R6 motorcycle
600cc 4-cylinder 4-stroke engine
Ambient temperatures averaging 70°F
Standard Cooling (before Evans):
Average freeway/moving operating temperature: 185°F
Typical temperature for fan activation: 219°F
Typical temperature for fan shut off: 210°F
Typical "heat soak" temp after engine shut off: 229°F

Evans Cooling:
Average freeway/moving operating temperature: 200°F
Typical temperature for fan activation: 239°F
Typical temperature for fan shut off: 236°F
Typical "heat soak" temp after engine shut off: 246+°F*

*at this point, the coolant warning light would activate

Distilled water + water wetter:
Average freeway/moving operating temperature: 181°F
Typical temperature for fan activation: 219°F
Typical temperature for fan shut off: 209°F
Typical "heat soak" temp after engine shut off: 223°F

I've since tried to get in contact with the engineering division with Evans Cooling to figure out why the heck this happened. But, because of the three hour time difference from California to Connecticut, I've been only able to play phone tag with him. So...until I can in contact with Steve Pressley (the engineering guy), I think I'm gonna put this on hold for now.

Great thread on Evans NPG+

RX7.com endorse it know as well as Pineapple, Snake oil? I don't think so, but it sure is expensive.

I just wanted to add that every car/engine that I've run/seen (whether it be by accident or not) without a thermostat has overheated. This most recently happened to a buddy of mine whose car would overheat every time it went down the drag strip (keep in mind that he spent some time staging). The system was burped by several experienced people and we were certain that it had no air trapped.

He figured removing the t-stat would allow the coolant to flow faster and do a better job. A t-stat with a couple of holes drilled in it fixed it. (as previously mentioned here)

I don't know all the physics behind it, but what I do know is that I've never seen thermostat-less cooling system not overheat. Obviously the t-stat (even when fully open) provides some kind of "restriction" that was designed into the system.

Sonny

Sonny,

its known that some restriction is necessary. If you goto mazdaspeedmotorsports website....then goto tech, then to cooling it talks about gutting the thermostate but leaving the casing in place and pluggin the bypass

http://www.mazdamotorsports.com/weba...ubject=cooling



Water Pump/Thermostat

If you are using a stock (cast-iron) water pump, we recommend "gutting" the stock thermostat, leaving just the thermostat casing. Because some "restriction" is helpful, generally removing the thermostat is not as effective as using a gutted thermostat or restrictor. It is also important to plug the thermostat housing's water bypass. This can be done very easily by tapping the hole (1/2" pipe tap) and installing a plug.

Good link, man. Thanks! :)

Sonny

Wow!! Another NPG+ thread..
I'm not an expert in this.. but more and more I start to understand about rotary engines and etc.. I'm starting to not believe in using NPG+.. My reasons are as follow:

As my builder started to build my engine, I realized how important lapping and specing all internal parts.. I've bought 5 used, mostly coolant failure engines and all have distinct rear plate failure... 3 out of those 5 engines were Mazda Reman with less than 20K (one build in 99 with around 15-18k, 2001 w/ less than 11k, and unknown year with less than 20k, just looking at the turbo manifold and apex seal).

With my limited knowledge in this field, I think its more harmful to run the car hot than to run 0 cooling system pressure.. I'm more afraid I'm doing more damage to a car thats running 20+ degree higher all the time than afraid of having boiling spots.. But thats just my take on this..

Ok, the people running Evans coolant with 7lbs. pressure; where did you get the 7lb. smaller radiator cap? I can't find one anywhere!

The restriction is to ensure that there is enough dwell time for the coolant to pick up heat and release it.

The reason that cars overheat w/o a thermostat is because there is a hole in the back of the thermostat housing. When the thermostat is not opened, 90% of the coolant flows back (i.e., bypasses) into the engine block via this hole to ensure faster warm up. Once the thermostat opens up, it moves into and block the bypass hole.

W/o the thermostat, coolant wil just bypass back into the engine rather than flow to the radiator.

Boiling spots mean uncontrolled thermal expansion. Uncontrolled thermal expansion will ruin whatever tolerances you have spec'd into your motor.

FWIW, Ferrari runs pure water with a 45 lbs pressure cap for a boiling point of 278 degree F. Evans is about 10-20 degrees higher in the coolant temperature. I don't know what the metal temperature is but it's not uncontrolled thermal expansion.

just to add my own knowledge of it in, the npg+ coolant will run slightly hotter than a standard H2O + AF mix...

great thread....

pomanferrari is all wet on this dwell time BS. No restriction is required for dwell time for the coolant to pick up heat, standard coolant or NPG...

I am running 7PSI but I have the rx7.com AST. It uses the standard size radiator cap available everywhere. Maybe if you havent already done so, an AST upgrade with that in mind could be worth your while.

Just wondering, what kind of pressure would I be looking at, at the point of boiling spots??

I have the 7lb. for the AST, I was looking for the smaller radiator cap, the main unit connected to the thermostat. Don't you have to change both?

yup, my full explantion in a few posts in this thread.

https://www.rx7club.com/forum/showth...&highlight=npg

Unless you race, use a fresh, stock mazda 180F t-stat, with no drilled holes.

No, the one on the water pump housing should have no pressure relief in it at all, just a rubber seal around the top. The pressure is regulated by the cap on the AST.

Ive been considering NPG+ also since my recent "close call" with over heating. I dont think it sounds like a good idea as I also feel that a cooler engine is a happy engine, Its always going to get up to "proper operating temp." you probably wont be able to cool the system so much thats its inefficient for the motor with any setup you might have with a rotary...

I recently pulled the t-stat from my 91 ford ranger v6 because it was failing and my truck will not heat at all whats so ever regardless of the driving condition, I get no heat at all and the temp gauge does not rise off of the "C" one mm...

I think Im going to try the distiled water/watter wetter mix, Can you do that when storing the car in freezing climate? I dont know anything about watter wetter...?

Thanks

Oh! I have a 13lb. cap there, should I just get one with just a rubber seal, or should I just remove the rubber seal from the current one?