I agree with you. There is SOME height difference. The FD cooling system holds about 2 gallons. As for the radiator it has its endtanks at the top and bottom. The bottom endtank is lower than the lower radiator hose entry into the engine, and only water above this point of entry into the motor will be able to act to "push" coolant into the motor. The top endtank I bet holds under a quart, the core itself maybe another 1/2 quart (I bet it's less but let's stack the deck in your favor). Let's say there are 1.5 quarts of "cool" coolant available after shutdown with the radiator fans running.



Not at all. I'm one of the folks who hates misinformation and when facts are presented with just enough information to make someone dangerous. I understand the science of convection and the requirements for it to take place. The FD cooling system does not present a good example of convection. Any convection that does take place is in such small amounts that its effect on shutdown temps is practicaly nil. Anyone smart enough to read a temp gauge can confirm this, regardless of where the probe is mounted.

I guess I am incapable of understanding your point. You're saying that regardless of what a temp probe inside the engine says, convection and therefore cooling is taking place even though our temp gauge informs us without a doubt that the coolant temp RISES after shutdown? But since the temp gauge shows an increase it must be wrong because you insist the coolant is in fact getting cooler due to convection as the car sits and not due to the fact the heat is just normally radiating out of the system on its own? All you have to do is monitor temps fter shutdown with and without the fans running. Running the fans makes practically no difference. But then we can't trust those temps gauges! They only count when the engine is on!

But we are not allowed to do that by using several temperature probes in the system? The stock probe is in the block and I have another in the throttle body coolant line. They both say the block stays hot no matter if the fans on the radiator run or not. But we have to disregard those? When may I believe my temp gauge is in fact telling me the temp of the coolant?


I do believe in physics and I do believe in convection. My point is that:

Exactly. The amount of coolant the radiator is capable of cooling and pushing into the system without outside energy (such as a water pump) is not enough such that it is not completely overwhelmed by the much larger volume of much hotter coolant residing in the rest of the system. In order for convection to make a contribution to lowering temps, the radiator would need to be MUCH bigger in volume compared to the engine block.

This is all confirmed by monitoring coolant temps in the block, thermostat housing or throttle body coolant line. Each of those locations tells us the the engine in fact heat soaks after shutdown and coolant temps rise. They finally decline over time mostly due to the direct radiation of the coolant's heat through the components of the engine and cooling system.

Most people would say the FD radiator is barely adequate even when the water pump is running, but yet somehow after shutdown the magic of convection makes our radiator super efficient and able to push coolant throughout the system on its own accord bringing cooler coolant and lower temps to all the happy little rotary engines!

So everyone who claims that FD's have terrible heat soak problems after shutdown completely misunderstand the problem. Your car may feel very hot, and your temp guages may say it's very hot, and you may even hear very hot coolant boiling in places, but all you have to do is insist that convective cooling is happening inside your cooling system and you shall never have to worry about shutdown temps again.

The ignorance; it shall set you free!

 

The amount of convection cooling in an FD cannot be significant. The layout of the car prohibits it. I doubt that convection cooling would lower temps more than 2 degrees over a 15 minute time period. 2 degrees doesn't matter.

 

Ok, usually you are the man, but I think you are wrong this time. I've got an intake temperature sensor just past the intercooler ($9.99 at radio shack). Without the fan mod it would regularly go up to 140 F due to heat soak. This would happen when parked or at stoplights. With the fan mod I see almost no heat soak, although sometimes 10 minutes isn't enough (!) to prevent it when parked. Just park your car in the garage with the fan mod.
It's like having a free space heater.

 

Got a part number, pic or description?

 

What I notice is when I leave the fans running after shutdown the coolant in the radiator is much cooler...so when I start my car, the cool coolant instantly cools the motor back from around 210F (9:30 o'clockl) to the normal cold mark on my linearized temp gauge.

Fans off - doesn't drop as much on a hot start.

But with the fans running it's pumping hot air from the radiator into my bay, with no where to escape...so my IC gets heat soaked like a mothafawker!!! If I'm parking at work and I'm not going to drive for hours...no problem. Otherwise - problem...fix IC sprayer.

just a thought

 

Personally I dont think heat soak after you shut down the car is that big a deal. I've never worried about it and dont plan on starting now.

According to my PFC my temps after shut down have never got high enough to do damage anyway. In addition when they are high they come down to normal very fast. So whats the big deal???

STEPHEN

 

Actually, your engine bay, including your intercooler, will heat soak much worse with the fans off.

If you have cooled your car down properly, you should be turning you car off with the engine temps under 200 degrees (I try to shut mine down at 180). So, after shutdown, you have fans sucking cool air into the radiator. For the first minute, the air going thru the radiator is heated. Lets say it's 75 degrees outside. Lets also say that the air passing thru the radiator spends 1/100th of a second in contact with the radiator. That air will not be instantly heated to 200 degrees. At most, it might be heated around 30 degrees. So, for the first minute, you are blowing 105 degree air thru the engine compartment. After a minute, the radiator will no longer be providing much heat at all, as the fans have cooled the tubes quite a bit. So, now the air blowing into the engine compartment isn't much hotter than the outside air.

The air from the fans escapes the engine compartment in the same manner that it would escape if you were driving down the freeway. Most of it goes under the car. Saying that it has nowhere to go just isn't accurate.

With no fans, the radiant heat from the engine, and radiator will heat everything in the engine compartment to something well over your coolant shutdown temperature.

 

I use that trick at the track all the time; it works great. Pop the hood, shut down the motor and let the fans run for a few minutes. Then restart the motor to pump the "cold" coolant into the engine and refill the radiator with "hot" coolant. Let fans run again...

It works great at keeping the coolant temps under control when it's 100 F degrees outside and your FD is a two driver car at the autox. I also carry a garden sprayer and soak the a/c condensor as the engine idles with the fans running; this draws cooler air across the radiator. I give the intercooler a nice bath every few minutes up until running and then give a nice burst of water to the inside of the intake and intercooler duct before dropping the hood and staging.

 

I shoot for about 180-190 F when autoxing and can usually make it as long as I have about 10 mins before the next run (more if it's summer time here in Texas). FWIW I never run the car hard unless I see at least 180 degrees on the coolant temp.

Or you can just pop the hood. Works even better at fighting heat soak

 

Popping the hood works great if you can stay with your car, or if is in a safe place (garage). I used to pop the hood at night when I parked the car in my garage. Many times I would come out the next day to find a weak or dead battery. It turned out the my alarm system was sending a signal all night, telling the "brain" that my hood was open. It does this even if the alarm is turned off. So, leaving the hood open for very long isn't an option for me unless I pull the alarm fuse every time, which is too much hassle!!

 

That's really odd. The alarm is upset the hood is open yet doesn't trigger?

 

IMHO - You can only appreciate the ability to manually control the fan if you first have and can easily monitored and accurate temp guage. If you run the car without AC in traffic or on the track it is nice to just flip a switch and watch the temp guage drop. I have the miata thermoswitch (which does require that you cut the harness and install a new plug BTW) and I still use the fan mod switch. At auto-x and track days it is nice to be able to pop the hood and let the fans run with the car off to cool it down. Befor I installed the fan switch I used to pull the AC relay and use the AC control to kick the fans on high but the seperate switch is much easier to use.

 

Yeah, it's weird. It's a Clifford alarm with a hood sensor. Even when the alarm is off, the sensor sends a signal when the hood is open. The constant signal drains the battery. I sent two "brains" back to Clifford because I was told they were defective. Turned out to be the hood latch sensor.

 

Well, if honegod's convection theory were correct, you wouldn't be seeing this behavior.

I agree with DamonB 100%. I think honegod has just enough knowledge to make himself sound correct, even in the face of *experimental* evidence that discounts his theory.

 

I am seeing it as a cumulative effect sort of thing, add one practicaly nil to another, to another, and you start to get measurable results.

and the practicaly nil in this case is all 100% goodness.

Quote:

But then we can't trust those temps gauges! They only count when the engine is on!
When may I believe my temp gauge is in fact telling me the temp of the coolant?

the problem with the senders is exactly that the flowrate is so drastically reduced.
when the pump is running the flow is swift enough that pretty much anywhere you have a sender it will tell you the overall temperature of the coolent as it flows past.

when you convert to convection the flowrate is no longer swift enough to even out the temperature of the water AT ANY SPECIFIC POINT. instead of reading the average temperature of the water the sender only reads the coolent temperature at that specific point.

so placement of the sender becomes critical because different points of the engine have different ammounts of heat energy stored in them.
that energy will flow around trying to even out.

so if you put your sender where there is little energy stored but near to a area where much energy is stored, your guage will read a rise in temperature as the heat flows from the hot area to the cooler area where you mounted your sender.

you will have great difficulty in seeing an increase in the rate that the HOTTER area cools because your guage only sees the COOLER area.

the difficulty I was talking about in placing senders lies mostly in finding those hotter areas and the cooler areas.

keep in mind that there will be convection internal to the engine, mixing the coolent as the engine equalises its temperatures, totally independant of the radiator and thermostat.

Quote:

The amount of coolant the radiator is capable of cooling and pushing into the system without outside energy (such as a water pump) is not enough such that it is not completely overwhelmed by the much larger volume of much hotter coolant residing in the rest of the system. In order for convection to make a contribution to lowering temps, the radiator would need to be MUCH bigger in volume compared to the engine block.

a part of our problem here might be that I am happy if there is a 2% increase of the rate of cooling the overall engine, if the heat energy leaves the system 2% faster due to convective cooling, you seem to want to see more dramatic results, which would be excellent, but not what I am after with this.

Quote:

This is all confirmed by monitoring coolant temps in the block, thermostat housing or throttle body coolant line. Each of those locations tells us the the engine in fact heat soaks after shutdown and coolant temps rise.

aye, coolent temps at those points rises as the hot engine parts dump their heat into the water, cooling them and heating the water.

wouldn't it be swell to give that hot water someplace cool to go to shed all that heat ?

Quote:

They finally decline over time mostly due to the direct radiation of the coolant's heat through the components of the engine and cooling system.

radiation being no where as effective as airflow, having the fan blowing cool air across the engine will cool it much more rapidly than the engine radiating the heat energy into the rest of the engine compartment. {which will radiate that heat BACK into the engine }
plus the airflow cools the irradiated componants removing the heat being added to them.

note that the radiation still happens, so now we are cooling the engine with air, radiation, AND coolent convection.

Quote:

Most people would say the FD radiator is barely adequate even when the water pump is running, but yet somehow after shutdown the magic of convection makes our radiator super efficient and able to push coolant throughout the system on its own accord bringing cooler coolant and lower temps to all the happy little rotary engines!

neat, ain't it

Quote:

So everyone who claims that FD's have terrible heat soak problems after shutdown completely misunderstand the problem. Your car may feel very hot, and your temp guages may say it's very hot, and you may even hear very hot coolant boiling in places, but all you have to do is insist that convective cooling is happening inside your cooling system and you shall never have to worry about shutdown temps again.

I think it might help a bit if you actually did something to help that convective goodness happen, after all without the fan running the radiator has no way to shed the heat of ITS water, unless you open the hood to allow the radiator to convect air through it to cool the water so IT can convect through the engine.

Quote:

The ignorance; it shall set you free!

it ain't so much what you don't know that hurts you, it's what you do know , that ain't so, that does the damage.

 

Crikey....this is all such a bunch of , talking around in circles....

 

Well convection works on the principle of the difference in temperature and thus density of the fluid, right? So how about we get the biggest dang difference possible. We throw away the water pump and just put bigger fans on the radiator while blowing a mist of ice water over it. Now we have super duper hot coolant in the motor, and icy cold coolant in the radiator. Huge temp differences! Let convection commence! Boy, engine temps would plummet! And we'd never have a need for power sapping pumps! Why has nobody thought of this before? Why do they make everything so complicated?

Well shoot. You mean it's impossible to measure temp in a standing body of any fluid? Well I'll be danged Temp sendors are just big fat liars no matter where they are in the system. There's just no place you can put the little suckers to read actual coolant temps in the block.

The radiator doesn't convect anything; it radiates heat from the coolant into the surrounding air (hence the term "radiator"). If air is actually passing through the radiator rather than being stagnant, the radiator becomes much more efficient at radiating heat from the coolant. Thus, we add fans and encourage air to flow through it when the vehicle is in forward motion.

The whole reason your engine requires a water pump is because that without it the coolant will not circulate through the system. There are systems that use convective cooling, but I think you should quit trying to prove it happens in cars and stick with your nuclear reactors.

Convection ain't gonna do sh*t in an FD. The volume of coolant that the radiator is capable of cooling is nothing compared to the volume of coolant the engine is capable of heating up after shutdown.

It's like dropping an ice cube in a hot cup of coffee. Sure, the temp of the coffee must drop a slight amount since it melted the ice cube, but you're still left with a really dammed hot cup of coffee.

I will leave it alone now as you seem to be backtracking from the idea of convection providing cooling to the engine block and now are saying it was all just a big experiment. Your happy to say if only a few molecules of coolant get from the radiator to the block without any outside forces that you were completely right. But yet you still have to try and muck it all up with temp sender locations, 2% increases, radiation etc so we can admire your "science".

Theory and the application of said theory are different. You can't form examples and applications of theories by wishing.

 

...what I meant by "talking in circles"

...or somewhat uselessly resurrecting and elongating a thread by nitpicking on the minutia of someone's post on something already proven by practical means. If I remember correctly, this is the 3rd Gen forum, not Thermodynamic Science Journal.

 

You should add that to your sig. You use it a lot

The third gen section has mods too. PM them and ask this to be moved, pruned, deleted, whatever you wish. Doesn't hurt my feelings any.

 

sorry if I am being frustratingly nitpicky, I just saw an incorrect idea being accepted and thought it worthwhile to try to improve the general understanding of what is happening.

when trying to improve a cooling system it is helpful to understand what is happening.

if your theory is flawed, you will have to rely on luck for good results.

my theory is strong, where I am lacking is in the diplomatic skills to present it in a way that does not generate resentment.


heh, the radiator transfers heat energy to the air flowing through it by direct contact, not radiation.

 

Well, I guess I just hoped that the circular meanderings (honegod's posts, not the ) would run out of gas and come to an end....

 

Its an indoor/outdoor thermometer. Little white box with lcd readout. Runs on triple A batteries. The one I have is not wireless (most of the new ones are). I just hung the 'outdoor' probe (which has about 10 ft of wire) in my intake just past the intercooler. Probably need something more robust for long term use, but it's been very useful.