Engine Temps

[cdigerlando]

Anyone know the normal stock idle engine temp? Mine runs at about 87 C. I was thinking of replacing the thermostat with one that opens at 60 C instead of 70 C.

[svxcuseme]

( 87 C), 188.6 F sounds about right. I tried purchasing a lower thermostat at advance and autozone, but the lowest either had was 170, (stock).

Where did you find a stat that opens at 70 (158 F) and who is the manufacturer. I'd like something like this for winter months. I've removed mine completely for the summer.

[ItsPeteReally]

I've removed mine completely for the summer.

This does seem to be a "band aid" solution to your problem, whether it's a real or imaginary one.

In reality, an automotive powerplant dumps so much energy into the cooling system that opening the thermostat earlier, or even dispensing with the thermostat entirely, is largely irrelevant.

If the cooling system cannot keep up with the engine's rate of waste heat generation then the problem almost certainly lies within the radiator itself, or perhaps, the water pump's ability to transfer sufficient quantities of water from the engine to the radiator.

If the radiator cannot keep up with the engine's "wasted" power output then fiddling with the thermostat might, at most, buy you another mile or so up the road until the radiator 'boils over" but it aint a permanent solution.

[cdigerlando]

Originally Posted by svxcuseme

( 87 C), 188.6 F sounds about right. I tried purchasing a lower thermostat at advance and autozone, but the lowest either had was 170, (stock).

Where did you find a stat that opens at 70 (158 F) and who is the manufacturer. I'd like something like this for winter months. I've removed mine completely for the summer.

Crucial racing sells one for the WRX, which is the same as ours. Look up the part numbers. It should work in our car. Problem is it is $60. The benifit of this remains to be seen, as was just brought up, although the vendor claims some good temp reduction. http://www.crucialracing.com/products/coolsafe.php

[ItsPeteReally]

The benifit of this remains to be seen, as was just brought up, although the vendor claims some good temp reduction.

If the cooling system is in good condition, and has sufficient excess cooling capacity, then fitting a lower temperature thermostat will reduce the temperature of the coolant ever closer to that of the ambient external air.

Quite why anybody would want to do this intentionally is beyond me. The whole purpose of the thermostat is to ensure that the coolant temperature is raised to the minimum temperature at which the engine starts to operate somewhere near its optimum efficiency.

The standard cooling system was designed to let the car run flat out in the hottest air temperatures imagineable. Under these conditions the water temperature may well be raised to over 100 C, which is why the system has a pressure cap!

Under less stressful conditions, and certainly at idle, the cooling system should be more than adequate.

If you do have cooling issues (and I'm not convinced that you do), then the first, and easiest, place to look might be the airflow through the radiator. Is it bunged up with dead flies, leaves, feathers etc.?

If that's O.K, then are the fans and their shrouds undamaged?

If all of that seems O.K. then perhaps the radiator itself is silted/furred up internally, or perhaps the water pump is on its last legs.

[cdigerlando]

Originally Posted by ItsPeteReally

If the cooling system is in good condition, and has sufficient excess cooling capacity, then fitting a lower temperature thermostat will reduce the temperature of the coolant ever closer to that of the ambient external air.

Quite why anybody would want to do this intentionally is beyond me. The whole purpose of the thermostat is to ensure that the coolant temperature is raised to the minimum temperature at which the engine starts to operate somewhere near its optimum efficiency.

The standard cooling system was designed to let the car run flat out in the hottest air temperatures imagineable. Under these conditions the water temperature may well be raised to over 100 C, which is why the system has a pressure cap!

Under less stressful conditions, and certainly at idle, the cooling system should be more than adequate.

If you do have cooling issues (and I'm not convinced that you do), then the first, and easiest, place to look might be the airflow through the radiator. Is it bunged up with dead flies, leaves, feathers etc.?

If that's O.K, then are the fans and their shrouds undamaged?

If all of that seems O.K. then perhaps the radiator itself is silted/furred up internally, or perhaps the water pump is on its last legs.

You make a lot of good points. Radiator efficiency is very important, not to mention the thermostat function and the water pump. All very important operating parts of the cooling system which must work. The vendor claims are that the thermostat only slightly lowers the opening temperature. It does not set the thermostat to a super low ambient air temperature. This would be similar to removing the thermostat all together. Also they say that the thermostat reacts quicker to changes in temperature, which would definitely be true if the opening temperature is lower. One other good point brought up by the vendor is that with aftermarket radiators, the coolant temperature will be much lower. This can constrict the flow through the engine which would be bad from a local heat standpoint. In other words our engines are hot but the cool water in the radiator is not allowing the thermostat to fully open.

I also would tend to agree with you that on a stock engine, the stock cooling system should be work fine to cool the engine, provided all of the parts are working. However, my engine is not stock, and I am expecting a bit more heat from my boosted cylinders. Eventually I would like to run an aftermarket aluminum radiator. I also have installed an external ATF air/oil cooler. This should reduce the heat applied to the radiator as well.

If you have not already, read the vendor claims from the link and tell me what you think. I would be interested to hear what you think.

[ItsPeteReally]

If you have not already, read the vendor claims from the link and tell me what you think. I would be interested to hear what you think.

O.K. I've read it now. It's pretty obviously an advert, they do want you to buy one so very, very much don't they?

I could never be as dogmatic about it all as they are, but then I have no axe to grind.

But, as a general principle, reducing the thermostat temperature is just plain wrong!!!!! It's attacking the problem from the wrong end, and is an ineffective solution too!

Let's assume that your turbo equipped car is dumping more waste heat into the cooling system. That is going to be undeniably true if you've got a lead foot.

What the cooling system has to do is remove that waste heat from the coolant at a rate that is fast enough to prevent localised boiling of the coolant in the water passages in the cylinder head, which is a bad thing to happen. If the water does boil inside these water passages then the cooling system goes into catastrophic failure, things start to expand and warp, perhaps even seize up entirely.

So what would an engineer do?

Well several things, perhaps the most obvious thing is to size the radiator and/or water pump so that the heat generated from the engine can be effectively dispersed into the atmosphere. I don't know how much safety margin Subaru engineers designed into the SVX's cooling system, or how much extra heat your turbo set-up generates. Unfortunately the standard temperature gauge is not measuring the water temperature at any one of the six danger points in the cylinder head next to the combustion chambers, but merely at a point that is convenient to get access to, so this is not going to be much of a guide, merely a 'rule of thumb' kind of thing - you are on your own here

Secondly, put additives in the coolant. You do, at least, have antifreeze in the coolant don't you? Even if there is no risk of frost, a good brand of antifreeze contains anti-corrosive agents and raises the boiling point of the coolant too. Some people swear by 'water wetting' agents too, they can do no harm.

Thirdly, a higher rated pressure cap will raise the boiling point of the coolant by a few degrees.

Lastly, try to improve the airflow through the radiator.

The thermostat barely enters the equation at all, once the thermostat is open, it's open, it cannot magically supply more cooling than the system is designed to provide.

Beware! Maths and physics beyond this point.

The miniscule safety margin that a lower operating temperature can provide is derived from about 9 litres of water running 17 C lower in temperature, (and the associated thermal mass of the radiator too which I'll guess to be approximately the same) will mean that it takes 2x9x17 = 306 Calories of energy to heat up that thermal mass which equates to 4180x306 = 1,279,080 joules of energy.

With me so far?

O.K. Let's further assume that your turboed engine is putting out 200 kilowatts of power (nice job!) it would not be too unreasonable to assume that at least 50 kW is being dumped into the coolant - probably much more.

Working the maths 1,279,080 / 50,000 = 25.6 seconds.

So, at the penalty of running the car inefficiently most of the time you have bought less than thirty seconds of engine protection. It doesn't seem a particularly good deal to me.

[svxcuseme]

Thanks for the info cdigerlando. I'll check into the WRX stats. Use of practical experience along side technical knowledge will go a long way.

Measure engine temps in the middle of the summer on your SVX, stop and go traffic, 92+ F ambient temp and you'll quickly see that a perfectly functioning factory cooling system will keep your car around 200+ F. That's great if you're concerned with keeping your emissions down and gas mileage up. If you're more concerned with keeping your engine at optimal temp for performance and longevity, ~180F, then use whatever means you can, within reason, to solve your particular dilemma. Over cooling is bad, but persistent and subtle over heating is just as bad.

[cdigerlando]

I agree with everything you are saying. The only benifit I think that is gained is that if I run slightly lower temps, a sudden spike would be better absorbed due to the lower temp. Thus response would be improved and keep temps from spiking so high. Also these thermostats lock open in the event of an overheating event. They don't fail closed (that is the claim anyway). I found one for $40 on a group buy at nasoic. I'll probably give it a try.

I believe that my original overheating problem was caused by some sort of air lock. I'm hoping that cycling the heat cycles with the radiator off will help remedy that situation. Currenty my car idles in Florida (95F ambient) at about 87C. Does this sound reasonable?

Also in the future I will probably be getting an aluminum aftermarket higher efficiency radiator. Anyone logged any engine temps using the new radiator?

[immortal_suby]

Originally Posted by cdigerlando

Also in the future I will probably be getting an aluminum aftermarket higher efficiency radiator. Anyone logged any engine temps using the new radiator?

Haven't logged anything with a separate gauge but going by the dash gauge there is no difference between the PWR and the stock radiator. Not sure how sensitive the dash gauge is though.

[Beav]

Another case of trying to be smarter than the engineers?

Leaving the 'stat at OE level and increasing the system's reserve ability is the answer. A $12 'stat seems like a cheap alternative to spending several hundred dollars to do it the correct way. But we all know you can't whip that dead horse hard enough to make it trot.

[Trevor]

Reference to not failing closed, would probably indicate a closed position whereby it would form only a restriction leaving a bypass flow. This is quite a normal arrangement.

The thermostat regulates, fixes, establishes, maintains, a specified operating and minimum temperature, as is its normal and exact function. It can have no effect on temperatures above normal, unless it is faulty and does not open at the preset figure. Unless it is not to specification and does not afford the correct rate of flow. Only spikes shorter than the thermostat reaction time could occur and the time delay in opening is not excessive.

[ItsPeteReally]

Originally Posted by Trevor

The thermostat regulates, fixes, establishes, maintains, a specified operating and minimum temperature, as is its normal and exact function. It can have no effect on temperatures above normal, unless it is faulty and does not open at the preset figure. Unless it is not to specification and does not afford the correct rate of flow. Only spikes shorter than the thermostat reaction time could occur and the time delay in opening is not excessive.

I broadly concur with what Trevor says.

For less money than that thermostat costs at the site that you indicated, you can buy a higher pressure radiator cap, which should make a real difference in delaying boiling problems, and it will enable the radiator to radiate more energy too, because the coolant can get hotter before boiling - that's basic Newton's law of cooling.

But higher temps and pressures mean you'd better have good hoses.

But the real solution still lies in having a radiator and waterpump that can dump heat as fast, or faster, than the powerplant generates it.