Isaacsracing

I was really surprised that I could not find a discussion on this already, but I couldn't.
My 968 race car blew about a gallon of water out of the overflow tube when I came into the pits at Lime Rock a few weeks ago. The car was fine on track and I did not notice if the gauge read high while I was on track. The car has an oversized radiator and the heater core has been bypassed. The cap was purchased a year ago to replace the one the prior owner had had. The cap being used is a 18-22 psi Stant cap. I have been using distilled water and water wetter rather than coolant, which is fortunate at least in the area of it not creating a mess of coolant! I would prefer to stay with water for track use.
Shall I put a higher psi cap on, such as a 21-25psi cap? Would I then be risking blowing a hose if there is a point in the hose or clamp that can't handle 25psi? Would it blow an engine seal and force coolant out somewhere else or force coolant to mix with oil? What are the risks?
Or is this just the totally wrong type of cap??
Thanks for your help!

H.F.B.

yes, that is ok. I too use such a cap.
WSM states -->

Isaacsracing

Thank you HFB-
The WSM of 1.3-1.5 bar is approximately 19-22psi. That's about what I had.
21-25psi is close to 1.45 to 1.7 bar. I'm concerned that there will be side effects of the higher pressure.
More thoughts, please.

Paul Waterloo

When you came into the pit, what were your radiator fans doing? Were they on high? It seems as if you no longer had the necessary heat removal rate from the system when you came off track due to lack of air flow and the radiator cap blew due to pressure. I would consider a manual cooling fan switch that you could select to high for the fans on your cool down and pit in time.

jsheiry

I remember reading something about these engines and demands of racing and that additional oil cooling was the way to manage the heat vs additional water cooling IE larger radiators etc... Wish I could find the thread and link for you. Here is a link to what seems like cheap insurance for a race car application...no affiliation but a setup I have read about http://www.rsbarn.com/catalog/index....roducts_id=153
Cliff was building something like this himself I think.....from a tiptronic cooler on the drivers side. Calling Cliff for report on oil temps....

PF

That is a copy of the solution Porsche had on the 968 Turbo S and RS models. Great factory upgrade.
Thermal management is very important

Porsche raced with the 944 Turbo Cups and the 968 Turbo RS cars with the stock 951 radiator. Dont think they ever had issues with water temps.

Like previous post I would investige fan operation and also triple check for any air in the system.

Isaacsracing

Considering that I didn't have this issue last year using the car 14 days, most in higher ambient temps than when this happened, maybe I did have air in the cooling system. Any tricks to be certain that the air is all out? With my street car, which still has a heater core, you can hear air gurgling if it's not bled and in order to bleed successfully, I jack up the driver's front corner, use a pressure tester, run the car with the heat on, and make sure that a steady stream comes out the bleeder screw near the front of the fuel rail. On the race car, I haven't jacked up the front corner, and there's no heat to turn on, but otherwise I follow the same procedure. Is there a trick I don't know?
I like the idea of RS Barn's double cooler, but I'm not doing that right now.

Paul Waterloo

To ensure the cooling system doesn't have air in it....you might consider the UView Airlift Cooling System Leak Checker and Airlock Purge Tool Kit. I bought one for my 996....which is not the easiest car to get the air out. OMG, the tool is over the top cool.


https://rennlist.com/forums/996-foru...il-leak-2.html