0.9 pressure cap... why not higher??
 

I've been taken a look at some japanese interviews and I've seen some FDs with 1.3 bar cap on their aftermarket ASTs. I've searched and it seems you don't recommend going over 0.9 pressure caps because the coolant system is not prepared for these pressures. But, which are the parts in danger exactly? The system gaskets, heater radiator, the hoses themselves?
It's known that the higher the pressure is, the higher the boiling point becomes, so theorically high pressures are better in order to improve cooling, isn't it? I'd like to understand which parts are not supposed to keep higher pressures :)

Mazda actually lowered the pressure caps in a TSB as there were reports of coolant hoses failing and catching fire (coolant is flammable).

you answered your own question..... AFTERMARKET.

I run a zero pressure cap with Evans NPG+ coolant. Yes, ZERO pressure. Oh, and my AST is eliminated.

So, for example, if you're running a full aftermarket hose kit stronger than stock, theorically it would be better (in cooling purposes) a 1.3 bars AST cap, do you mean this?

Zero pressure cap? I am not able to understand how your FD cooling system is working actually... :Wconfused

the main reason a cooling system is pressurized is to raise the boiling point of the coolant, Evans is a waterless coolant with a boiling point of +375F so boiling is not an issue, so unpressurized is fine

Doesn't NPG+ require a 0 pressure cap...

not required it will work on a pressurized system, but its not recomended, as it reduces cooling efficiency

ahum..... were do you get a 0 psi cap? I want one :P

all you have to do is remove the rubber seal on the bottom of the valve on your stock cap. but dont do this unless your running NPG+ otherwise your coolant will boil and youll be buying alot more than a new rad cap

yeah, its for NPG+. I was recently "sold" to it :)
I have to eliminate the AST also right?

"have to" no but if you decide to, it wont hurt anything. be sure the cooling system is properly burped before starting the engine, as the system is not pressurized, and as ive realized the AST elimination mod makes filling the cooling system about as exciting as watching paint dry but twice as long! Ive run without an AST with both 50/50 glycol/water and NPG+ and both work fine without it or with it. personal preference, but i personally see it as one less thing to fail and it cleans up the engine bay a little too

:icon_tup: Thanks! :icon_tup:

That would need to be ALL coolant lines, not just your radiator lines. IMO, I would try to run something which would require LESS pressure.

If your car runs on the hotter side the higher pressure cap will give you a higher boiling point, (less pressure = lower boiling point) it has no bearing on your cooling temperatures, if your car seems to run around the 200 degree F then that's where it will remain. Mazda (as stated in other threads) lowered the pressure to prevent (or lessen) the possibility of the turbo hoses developing leaks spraying coolant on the hot exhaust and causing engine fires. I for one went with The Evans setup and zero pressure for several reasons.

your temp gauge will read an average of the temp of the coolant flowing past it. one advantage of raising the system pressure and raising the boiling temp is to prevent localized boiling in potential hotspots. i dont know how rotaries are with this, but in a piston engine its a good idea because it will prevent the coolant in hotspots from boiling and letting areas around the combustion chamber get too hot and potentially causing detonation.

rotaries are more prone to local hot spors due to the higher combustion temps, but with a properly burped system, and running NPG+ it isnt anything to get too worried about on an unpressurized system

so how about a 1.1 bar?

Just a thought...

A car has coolant seals that are going, but not gone. The coolant only disappears after the system is pressurized, and does so in minut amounts. Would running a system with no pressure eliminate coolant loss to a certain extent? Would it constitute as a band-aid?

no, it might just make it worse

Explanation?

the cause of coolant seals going bad isnt the pressure of the cooling system. its generally heating and cooling again and again that causes the seals to crack and wear down, so running a non pressurized system may help, but it might give you like an extra week or so before they fail, and maintaining a 0psi system isnt cheap (but what is on an FD) the only benifit, in realtiy, is being able to add coolant while the cars hot, and it souns cool to say you run an unpressurized cooling system:icon_tup:

so then if i have an aftermarket ast its be alright to run 1.1?

You can run a 21 psi cap if you think your car is some how different from everyone else's. You've missed the point of why it was lowered to .9 bar any way so do what you want. Most the people that run the higher pressure:
1.) need to because there car runs on the higher side and need the added "head room" to avoid boiling over.
2.) track the car or are running a single turbo, and while the possibility of a fire under the hood exist, they are prepared to deal with it.
I still haven't figured out why using the Evans coolant would be considered a band aid, due to the fact that it's always a possibility the car may run a tad bit higher temperature. My interest in the Evans was the fact there's no water to introduce minerals in the system to help the metals eat themselves up (another cause of o-ring seal failure is the thin web gets eaten up) this is generally related to neglect of the cooling system. The zero pressure part is just a plus as well because there's no stress on the hoses and or water pump seal. I would suggest if your going to run higher pressure carry a fire extinguisher.

Details ... whats your setup and temps like? pics?

Me too!! My temps stay at 85-90 C (pfc) during normal driving and so far it has only gone up to about 94C after some hard 3rd gear pulls. I do have the fans to start at 87C and dual ducted 19row mocals.

I eliminated the AST by plugging the nipples at the bottom of the radiator and at the thermostat housing and using a FC filler cap with nipple to the overflow.

I like running with no pressure, it could save the engine in the event of a leak (I believe Damian went through this). The only downside is that the leak is hard to find! My WP started leaking from the gasket and I had the hardest time finding the damn leak! It was a really tiny leak (no pressure to force coolant out) and all I knew was that I could smell the coolant...

any higher than 0.9 will increase pressure on your coolant seals.

That was the impression I was under, which is why I suggested the Evans coolant could *possibly* be a band-aid for *slightly* bad coolant seals. I still haven't heard any knowledgeable information to answer this theory...

I think someone else was trying to say that this pressure difference between a .9 cap and the 0 cap version is too negligible, and that if the seals are to the point of wearing out, then switching from a .9 cap to a 0 cap wouldn't help much in terms of putting off a rebuild awhile longer.

However, if you started with a fresh rebuild, and over it's life, would a 0 cap help the longevity of the water seals over time?

How does a 0 pressure cap help in "light" tracking or autox events? or frequent safe street racing (if there is such a thing). I would think the extra pressure of 1.1 or 1.3, albeit a thorough hose upgrade kit installed for the radiator, turbos and TB and whatever else...

Works fine for heavy auto-xing, and street driving as well. Haven't tried any HPDE yet but car has seen some HSD.

Evans NPG-R hear, it is the best EVER

http://i19.photobucket.com/albums/b1...FDbuild003.jpg

You can still pressure test the system just as you would a pressurized one, so finding a leak shouldn't be any more or less difficult.

How can you say .9 bar is a negligible difference from 0. That's 13psi compared to 0

IMO, the difference between 0 and 13 psi IS neglegible compared to the combustion pressures that the seals also have to withstand. However, if you are talking only about coolant leakage (not combustion gasses getting into the coolant) at any location in the system, obviously, 13 psi will make some difference.

Also, IMO, coolant seals and hoses, in good shape, should be able to EASILY withstand either 13 or 16 psi. 13 psi just gives a little more safety margin (compared to 16 psi) if anything is in marginal condition. And, 0 psi gives a significantly lower chance of (noticeable) coolant leakage.

Dave

So if an engine has coolant seals that are just beginning to fail, would switching to a 0 psi system delay the process? If so, how much?

IMO (and, that's all it is - an opinion based on theory, but no actual direct experience), you might gain a bit of time before it became too bad to drive. However, it all depends on the mode (corrosion, engine warpage, seal permanent set from overheating, etc.) of (impending) failure. So, any guess I might make would be worth what it cost you. You've seen all the posts - it's anywhere from instant major coolant loss and starting problems to lasting for months with minor leakage.

Dave

Coolant seals no only protect coolant from getting into the combustion chamber but the keep the gas from the combustion chamber out of the coolant. So while A zero pressure system may slow the coolant from seeping into the motor after shut-down,It will not keep the exhaust gases from getting past the seals either. And you would still be displacing coolant with air(well....exhaust). and that displaced coolant will just be exiting through your coolant overflow resivour.

I'm no expert on the subject either but I don't see evans working as "band-aid)
I may be totally wrong with my theory, so feel free to correct it.

very little if any at all.

No excuss but to keep your coolant "system" in top condition regardless of fluid used or pressure used.

Our engine compartments are hot, rubber decays. Change hoses like one changes suspension bushings (oh you don't do that)ok like an oil change just not as offen. I covered in turbo coolant hoses with heat shield material.

SO you would say that the coolant system put more pressure on the coolant seals than the combustion area of the engine,(not always where they fail but typically where it happens) most anyone who has rebuilt a rotary can tell you that carbon finds it's way into the coolant seal area and can cause failure of the seal.

Dave I have to agree with you in reguards to the combustion pressures, I personally don't believe the cooling system to be an issue with coolant seals but instaed a problem with the coolant hoses. My persoal belief is that the added pressure in the tubo hose area is where most failures ocurr and the reason the fires ocurr. With all the heat generated in that area and the addedpressure of the hoses expanding and acooling down this is what leads to the failure, since no one has been able to nail down a PM for changing these hoses I feel no pressure is a great way to extend the life of these parts without fear of an under the hood fire. Use of this coolant in no way will prolong the coolant seals them selves but may aid in prventing the deterioration of coolant seal groove that has been known to fail from corrosion or elctrolisis.

Is the carbon in the seal area a cause, or a result of seal failure? IMO, it is more probably a result of combustion gasses starting to leak past the seals.

Dave

I'm not so sure it's a result of the seal failing or just that it creeps in, in small amounts during startup from cold engine and hot combustion gases over time.It may also creep in as the different metals cool at different rates. Since seals or no seals, the metal surfaces seem to seal completely once warmed up so my guess is the seal is there for the time the engine is cold or compensate for minor irregularities in the surfaces (again just my take on this) but when you first start the car and the engine is cold the combustion chamber gas's must push small amounts of the carbon and exhaust gases into the seal area, while this is not always where they fail it is generally in the combustion area near the exhaust. I used the blockweld treatment on my car while searching for a donor engine and it lasted about a year before my pushing the car at normal boost levels finally caused it to fail again, so air must get between the housings some how and my guess is when the engine is cooling. Poor cooling system maintenance is probably the biggest reason for the coolant seal groove area as I've seen some where the coolant groove is all but non existent. Of course before some one catches a hose failure or any other cooling system component and over heats the car, I believe this adds to the eventual failure of the seals as while the housings may not warp drastically they probably allow more of the carbon and combustion gases into these areas. I'm sure there are some other engine re builders that can throw some insight into this.

As stated above running a higher pressure will not aid in cooling, just prevent boiling to a higher temp. If you're running so hot that the stock pressure is not enough then the solution is not in the cap.

BTW: I lost the original engine in my car to a coolant seal. I could run and boost all day long with no coolant loss or overheating. As soon as I shut the engine off it could fill the overflow tank and spill out. Then when it cooled and I'd start it up I'd get the ol' add water light.

Yep my car was the same way.

My car just started acting like this last week. So how long did your engine last until you had to rebuild it? This filling up the coolant before driving sucks. No problems while I'm running it though, and not even a hint of overheating. Just overflowing bottle after shutoff.

-Jeff

Not to give you false hope, but, as I'm sure you know, the virtually-identical symptoms can be caused by a bad or dirty AST cap...

Dave

Hey Dave,

My coolant overflow does overflow even when the engine is on sometimes when I let the car idle. Yesterday while I was trying to jump my friends car (with no success, his battery was way dead), and when I was leaving, we saw a little puddle of coolant on the ground, so i got out the car to see where it's coming from, it was the overflow. So I went to walmart and bought a replacement AST cap (I have a RP AST btw).

Today after work I open my hood before warming up the car, I open up my housing rad cap, and I was low so I fill that up (otherwise the low level coolant buzzer goes off). I'm on my way home, and I stop at the mail box to pick up some mail, and I leave the car running. I get my mail and drive off. I look in my rear view mirror, and I see a small puddle. So that is why I came to that conclusion. Would it also be because of my GReddy rad cap?

-Jeff

Another thought - could the tubing to the overflow tank , or the tank itself (at the nipple that connects to the tubing or elsewhere), be leaking? That could also cause similar symptoms.

The cap, if it doesn't seal around the outside, can cause the coolant to leak out there.

Dave