Open Road

I’m sorry to monopolize the forum with DE questions you guys but opinions welcome again.

Last track day was ambient temp 83F, high humidity.
Driving hard with consistent boost for 20 min sessions per. Roughly every 60 minutes.

I’m running g40 coolant. No water wetter this time.
Temp gauge on cluster reaches early red section by mid to late session.
Independent temp gauge in upper radiator hose (essentially bridge temp) was 212-218F.

I’m thinking this is acceptable with pressurized systems but mentally 212F always makes me leery.


Question one:
What is a 928 coolant pressure range? I assumed 10-15 psi.

Question two:
What temp triggers coolant temp warning light?
I saw a factoid somewhere that number was 244F, but could not verify.
Additionally, what activates the light? I’m VEMS converted. Is that circuit in the pod?

Question three:

There’s no room for more fans, and biggest aftermarket radiator already exists.
If I need to I can run an additional exchanger from the heater lines. But, is that flow substantial enough to accomplish anything? I realize we are way into subjective territory.

Have you got an external oil cooler or is the heat from the oil going into the radiator?

Crumpler wrote: ↑Mon Oct 20, 2025 1:16 pm Temp gauge on cluster reaches early red section by mid to late session.
Independent temp gauge in upper radiator hose (essentially bridge temp) was 212-218F.

I’m thinking this is acceptable with pressurized systems but mentally 212F always makes me leery.

Give how much more-than-stock power you are putting down those temps are somewhat-surprisingly OK to me.

212 with a pressurized system, on track is ok.

I would, however, also want a notion of oil temperature. You can get an indirect idea from idle oil pressure. But, direct temp sender would be better.

83°F is a moderate ambient temp. When temps get to 90, 95+ you should expect coolant temps going to go up by *more* than the N-83° difference.

You should also "calibrate" your temp gauge versus direct measurement at the water bridge for at least three "needle positions" so that you know what the needle is telling you. (If you haven't done this already.)

What are you doing for oil cooling?

What about air-intake temp?

Crumpler wrote: ↑Mon Oct 20, 2025 1:16 pm What is a 928 coolant pressure range? I assumed 10-15 psi.

Spec is 1 BAR (14.7.) But, new caps are typically 14 +/- 0.5.

They do loose "oomph" over time. I'd do a release pressure test before every weekend.

Crumpler wrote: ↑Mon Oct 20, 2025 1:16 pm What temp triggers coolant temp warning light?
I saw a factoid somewhere that number was 244F, but could not verify.
Additionally, what activates the light? I’m VEMS converted. Is that circuit in the pod?

I think that 244°F (117°C) is about right. IIRC, I have seen info that indicates the warning threshold is 120°C (248°F.)

Me, personally, I'd be uncomfortable with coolant temps above ~230°F.

The idiot light is not triggered by the gauge sender. IIRC. But, I might be wrong. Look in your wiring diagrams and trace back from the cluster.

Crumpler wrote: ↑Mon Oct 20, 2025 1:16 pm There’s no room for more fans, and biggest aftermarket radiator already exists.
If I need to I can run an additional exchanger from the heater lines. But, is that flow substantial enough to accomplish anything? I realize we are way into subjective territory.

I'd gather more data: oil, IATs, "calibrated" temp.

If you are using the side coolers in the radiator, plumbing-in a external oil cooler before the side tanks could make a big difference. See Sterling's thread about his "under radiator" oil cooler.

Good points on oil cooling. I did not consider that.

Current set up is a ten row stacked plate cooler, out in front of the radiator. But I could go bigger.
I don’t have a temp sensor, only pressure.

The IAT numbers are not “bad”.
With the feed under the fender, and the special air/water intercooler Hacker sold me.
I don’t have live track data, but PC link on summer street driving with sustained pulls at boost run 68 to 80C.
I will say the prochargers themselves read 167F with the IR gun after a session.

Thank you guys again for the feedback.
It really does help me continue to improve the car.

Crumpler wrote: ↑Mon Oct 20, 2025 6:30 pm Current set up is a ten row stacked plate cooler, out in front of the radiator. But I could go bigger.

With coolant temps in the 210-220 range I would expect oil temperature to be 230-250.

With the oil cooler in front of the radiator, I would expect air exit temperature from the oil cooler to be a significant hinderance to maximizing coolant cooling.

The 90+ have a separate oil cooler mounted below the radiator. It's attached to the bottom of the chassis structure that retains the bottom rubber radiator mounts. (Again see @maddog2020's thread.)

Depending upon data, an under-mounted cooler plumbed between the pump and you existing cooler might give you a good cooling boost.

Thanks Dave, I will look at that too.
And thanks for the extrapolation coolant temp to oil temp, I was looking for something like that.