UnderDog

Hi gang,

I just ran my first POC event at Streets of Willow three weeks ago in my '95 968 6spd coupe. It went well, but my "!" light was coming on and my temp needle was creeping into the red. I ran the aux fan AND blasted the heater, but this only helped temporarily. I even went so far as to gear higher when possible to keep the rev's lower until my session was done. The outside temp was 95-100 degrees, so maybe this is unavoidable? John at Black Forest service seemed to think this was somewhat unusual, but they couldn't find anything abnormal with the car. Can anyone help with this? Thanks!

Julian Allen

I'm inclined to think the radiators are overtaxed in our cars when they are raced in such relative heat. A couple of possibilities include a blocked oil thermostat (if your oil temp really goes up it can ask a lot of the water cooling system) and problems with the air flow across the radiator. If the duct work lets air leak around the radiator too much, you won't get the benefit of the airflow.
I went to a thicker core custom constructed aluminum radiator by Fluidyne along with a homemade "plenum" to direct air across the radiatior and corrected my cooling issues.

UnderDog

[QUOTE]Originally posted by Julian Allen:

Julian,
Thanks for the reply. What did it cost? I just bought the car a month ago and have already done the waterpump, thermostat, steering rack and suspension bushings, allignment and well, I'm flat out of dough... So I'm trying to make whatever solution I come up with pretty inexpensive if at all possible.

Dave C.

Julian Allen

I think the radiator was about $750 or so. Not cheap, but a core that wass about 50% thicker than the original radiator. The ducting was .065 aluminum which I formed myself.

si

a cheap and cheerful solution maybe to remove the thermostat entirely since even when fully open it restricts flow. If you live in an area as hot as it sounds then you certainly dont need it!!

si
91 951s (no cooling probs with UK weather!!!)

ed devinney

Methinks something may be wrong that the mechanics haven't found.

I had my 951S out last weekend at Summit Point WV, 3 days of 95 degree weather with about 90% humidity. I'm not fast yet, but even my fastest laps (120+mph at turn 1, I'm a wimp) didn't get the guage much over the first tick in 20-25 minute sessions. I'd expect a NA car to be easier on the temps.

Adam Richman

Whereas hitting the red sounds a bit hot, my car usually from lap two until cooldown will stay pegged at the 2/3rds mark. I have a low temp thermostat and am eyeballing that idea of yanking it altogether (anyone know the downsides to that?).

FlyYellow

I used to have a 951 and a 968 and had cooling problems on both of them. I was able to solve both of the problems using the same technique. That class of car seems to get serious air pockets.

Here is what I did... BURP the car.

Get one of those tools that pressurizes the system (usually used to detect leaks). I drained the coolant & re-filled it with almost all water. Hooked up the pressure and then disconnected the lower radiator hose and then topped it up with coolant. That seemed to get all the air pockets out and after both cars didn't go past the 1/3rd mark on the temp meter.

Hope that helps.

keith

Ok, ok, hold up a sec.
I need more information here:

"Get one of those tools that pressurizes the system (usually used to detect leaks)."

Where did you get this tool? Was it the one with the spring-tensioned, screw on coolant resevoir cap?

"I drained the coolant & re-filled it with almost all water. Hooked up the pressure and then disconnected the lower radiator hose and then topped it up with coolant."

Why almost all water? What do you mean by disconeected the lower radiator hose? At which end? At the waterpump? At this point did water come gushing out? When/how did you know if the air was gone? Why would the air come out there? etc., etc...

Don't mean to be a nuisance here, but if this method works, I need to know the details!

- AND -

Adam, there have been several articles about the 944 systems not flowing properly to some bad conclusion by removing the thermostat or even having the WRONG SEAL installed around the thermostat...

keith

bump.

Adam Richman

I too would like to understand this technique.

In the meantime, does anyone know what effect the rocks, pebbles, bugs that flatten the evaporator coil (heat exchanger ? whatever this apparatus is) do to the air flow cooling the radiator? I had thought that by removing the debris, a better air flow would cool the radiator better. Now I wonder if they opened bigger holes through which more air could pass.

Anyone know what is the best procedure (if advised) for straightening these fins?

Mark

Franz Blam Racing prepared a 968 for Mike Doolin a few years ago and they had overheating problems. One fix I heard they used (recommended by Porsche in Germany) was to mill the head .004" (ie only .002" more than Porsche recommends as SOP for race prep). This seems a bit radical for DE etc but FWIW.
Mark

keith

bump. (still after those secrets!)

Seattle944t

As far as the pure water part goes:

Pure water absorbs and dissipates heat much better than with a 50/50 mix with anti-freeze. Anti-freeze has horrible thermal transfer properties. If you run too much anti-freeze you will actually cause overheating because it won’t dissipate the heat, it just keeps absorbing and your temperature just keeps going up.
The main reasons to use anti-freeze are:
1) Corrosion protection
2) Freeze protection
3) Raise boiling point (Not too important with a pressurized cooling system)
So for a street car that doesn't see temps much below freezing a 70% water mix will bring the temps down a little and still keep the corrosion protection (but you must change the mixture regularly!). Adding some Red Line 'Water Wetter' or something similar will bring the temps some more. I run two bottles in my turbo and have never seen the water temps get near the second tick during 20-minute track sessions. It's usually pretty solid in between the two marks after the first few hot laps and stays there.

Ahmet

About removing the thermostat all together:

Without a block-off plate, some of the coolant will be re-circulated through the block, while only a part goes through the radiator. Drilling the thermostat is an idea, but it really isn't all that necessary if the car isn't highly modified. A low temp thermostat should cure all overheating problems, if there's not another area in the cooling system that needs attention, such as a small leak somewhere allowing the decompression of the cooling system, or a slipping water-pump, etc.
Ahmet