Is it possible to "Over Cool" my engine?

[Kemo]

Ok...here goes...

With the factory thermostat in place on my SC, is it possible to add too much cooling up front with bigger oil coolers? I was afraid to try the "Cool Collar" since there was not a thermostat there to protect against over cooling.

As always, any replies are appreciated.

[mtelliott]

Doesn't the thermostat take care of that? If it's get's to hot in back, the thermostat directs oil to the front. Once it cools down enough, the thermostat shuts off (stopping the flow to the front) keeping the operating temperature of the oil in the proper range.

Of course in Dallas in the summer, it might not ever shut off. But with extra cooling capacity, I would think you're golden.

[Craig 930 RS]

Nope - because when the thermo closes, the engine is a still a happy camper. In Plano TX, you will need that cooling capability later on - !

P.S. Let's see a current pic of your car

[Kemo]

Craig,

here is what ive got now...with the trees nice and green in Texas, I really should take some nice "shade tree" photos.

Ruf Bumpers, Paintjob and a ProCooler!

[Kemo]

Thanks for the input...i was thinking along the same lines. As long as the thermostat is working, it really shouldnt matter how big the oil cooler is up there. I just wanted to make sure.

Now ive got to do some cyphering (Jethro Bodine reference)

Thanks again for the comments.

[Craig 930 RS]

Hooo hooo! Beauty!

[Bill Verburg]

As mentioned an over sized cooler will keep temps at the t-stat opening temp of ~80&degC

For longest oil life somewhat hotter temps are desirable to facilitate boiling off of condensates. lower temps just indacte more frequent oil changes.

[cowtown]

Bill, do you have any suggestions about how to raise the temps? My car has a giant Setrab center mounted cooler, and it sits at 180F in everything but track driving. I have even blocked off airflow, but on the street it just doesn't get hot. Maybe an adjustable t-stat of some sort?

[bigchillcar]

colin,
i think the t-stat on my '74 opens at 170 degrees (probably plus or minus a little)..should be the same on your car. if you've got a big cooler up front, it's doubtful your car will ever see 180+ unless you're hauling balls on the track. only answer has to be a new t-stat that won;t open until the higher temp you want..unless you'd rather downgdrade that cooler..
ryan

[Wayne 962]

I like 180 degrees - that's what my car runs at. If you want hotter temps, then you need to tweak the springs in the thermostat...

-Wayne

[M.D. Holloway]

Kemo - there is an old tale that says the hotter the engine the more hP - I think it was started by engine parts salesman. I know that the by-products of combustion include H2O and you will need heat to help it vaporize. Of course, the combustion chamber will be much hotter than the boiling point of water but I would be more concerned with the aras that are seeing lower temps.

Your in Plano, you will like this. I had the Targa out last week end. The Saterday when it hit 100. Max and I were driving for 40 minutes with the engine never going below 4500 rpm's - the temp gage went to 100 but never past. I have a trombone cooler and kickarse oil - thats it.

You a Maverick PCA member?

[Zeke]

Completely stock cooling system here, a fender mounted row cooler. Never over 180 in normal driving and I believe that's what the t-stat is doing for the car. AFIC, if you run 180 long enough each time out, you will not get an excess of water (or gas) build up in your motor.

Two things: The oil will pass areas of the motor that will be hotter and it doesn't take 212 to remove water. It will go away with any significant heat as long as the amount of heat/time exceed the rate of build up. Short, cold runs are very hard on any car.

[Quicksilver]

I'm surprised no one took a pot shot at the Cool Collar.

I guess people are going soft here.

[bigchillcar]

I'm surprised no one took a pot shot at the Cool Collar.

pullllllllllll!..... (boom) 'fell like a stone..'

ask and ye shall receive..
ryan

[Grady Clay]

How cool is too cool and how hot is too hot are just the extremes of the same line. Our air cooled 911s don’t have a very sophisticated cooling system. Under some circumstances it runs too cool and others too hot.

Yes, the addition of a thermostatically controlled front cooler in addition to the thermostatically controlled engine cooler helps. The real issue is the air cooling that is not thermostatically controlled. In cold weather and light loads the engine is over cooled and the oil temperature can never get to the thermostat opening point. In hot weather, air conditioning, and track loads the engines can get to extreme temperatures and can be damaged.

The correct combination is to restrict the cooling in cool weather to the point where the oil temperature gets to the boiling point of water. This allows the combustion water vapors and unburned fuel to be boiled out of the oil – 210F oil and 375F heads are about right. Just the opposite is true in hot weather, A/C on full, and on track. In this situation you need maximum cooling capacity so the temperature is always controlled by the thermostats and engine cooling fan – 180F oil and 275F heads are about right.

How is it possible to meet these two seemingly contradictory situations?

First is to have huge oil cooling capacity with large oil radiators and additional forced air fans to the coolers. In cool/cold weather disable the fans and block off most of the air flow to the coolers. In the cool/cold weather you want the oil in the coolers to be up to temperature and flowing fully.

For keeping the engine properly cooled don’t rely on the oil cooler. In hot weather the 1.82:1 engine fan ratio is a must in my opinion. This provides additional cooling to the hottest parts of the engine; the heads and cylinders. For track use additionally the “Rubbermaid Solution” is very worthwhile. For cold weather the 1.3:1 fan ratio is desirable. For extreme cold weather (below 0F) an even lower ratio is desirable. Yes it is a pita to change fan ratios but necessary in many circumstances. An added advantage to the 1.82:1 ratio fan is that it improves the A/C functioning.

Due to our pre-war VW heritage and some stubbornness, the 911 never got any air cooling regulation. This is partially because of the technical complication of a variable speed engine cooling fan. I would have preferred a vastly larger air cooling system and then return (recycle) some air in cold and warm-up conditions.

Porsche finally solved the problem: Water cooling and oil-to-water heat transfer. Clearly the water cooled heads solved several problems. During warm-up the engine warms to operating temperature much faster. That includes the engine and transmission oil because there is heat flow from the engine coolant to the engine and transmission oil during warm-up. Once the engine and transmission are up to temperature the heat flow is regulated the other direction to the cooling radiators.

The additional benefits are the reduction to propensity for detonation allowing much higher compression ratio. There is the additional advantage of a 4-valve combustion chamber with a centrally located spark plug not reasonable with air cooling. Of course the A/C and heaters also work better.

I have my Nomex on – flame away.

Best,
Grady

[bigchillcar]

grady,
are you saying that WATER IS GOOD?! for shame, grady..for shame..
ryan

[bigchillcar]

actually, very good observations of the practical limitations that our wonderful air-cooled engines approach at either extreme of heat and cold. i'm going to save your reply for future reference when trying to explain to someone else. it seems a future application in 'automotive science' could be something akin to our current engine ignition and fuel management systems - perhaps a 'smart' temperature management system that works to maintain this temp ideal in all weather/stress conditions?
ryan

[Zeke]

Grady, are you saying that 180* oil won't eliminate water? You are probably correct, given your experience. I didn't research the fact, but rather, based my conclusion on what happens to water in a 180* pan on the stove. It doesn't stay around long. Of course the oil does come in contact momentarily with hotter surfaces and has the opportunity to boil off water there.

I just wonder about pretty much 180* most of the time during average weather. Not hot enough?

[Grady Clay]

Milt,

My point is not so much about the absolute temperature as it is about the desirability to run warmer in cold weather and cooler in hot weather. Yes, the water and fuel will evaporate at 180F, just more so at 210F. The other issue is there is more unburned fuel in an engine running cold on the thermostat and more water condensing on cold internal surfaces. We have all seen liquid water condensate pouring out of someone’s tail pipe on a cold morning. Some of that gets past the rings and into the oil. Well, maybe not in Long Beach hehe. If anyone sees the white froth of emulsified oil and water on their oil fill tank cap, the engine hasn’t been hot enough in cold weather.

On the Forum there has been lots of discussion about driving technique and the importance of fast and complete warm-up every time the 911 is driven. Similarly there has been lots of discussion about 911s running “too hot,” lack of calibrated oil temperature gauges, and the extreme head temperatures not measured.

Air cooled VWs addressed the issue long before Porsche with thermostat controlled fan inlet restrictions. Even the “American” heaters on 356s and 912s tended to restrict the air flow when cold (mostly to get any sort of heat to the cockpit and windshield.) This had the (probably unintended) consequence of faster warm-up in cold weather. In hot weather those engines were very thermally stressed even at sub-100 HP. On my old 40 HP I used a large 36 HP crank pulley to turn the fan about 30% faster.

Many racers have heat pads attached to the sump tank and case and use a propane heater to warm the engine and transmission on cold mornings. I have seen some with air restrictors that fit over the fan housing and belt to let the engine warm-up faster at low throttle.

I’ll stick by my recommendations for modifications at the environmental and use extremes; even just summer to winter depending on climate. Not all of us operate our air cooled 911s only at STP.

Best,
Grady

[mjshira]

ahhh, wouldn't worry too much as you live in Big-D... it stays hot there most of the time, no? ;-) (I used to live there)