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      05-15-2011, 11:41 PM   #251
The HACK
Roger Murdock
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Drives: 2006 MZ4C, 2015 Fiat 500e
Join Date: Oct 2007
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Quote:
Originally Posted by PeterM1 View Post
Interesting news: I logged water temps for the first time at the track and the result was well, interesting: I'd hit ~98C at the turns, drop to 90-92C on the straights and then water would skyrocket to 109C the moment I pit-in (driving through the paddock). This was consistent across all sessions over 2 days.
Would it surprised anyone if I have a theory on this?

The turbo(s) on these cars are cooled by both oil and water. There's a heat exchanger between the oil used to cool the turbo while in operation, and water used to cool the engine.

So while the car is moving at high speed, there's more airflow going through the radiator, therefore cooling is more efficient even if you're at higher boost and full throttle. And the second you pit in the radiator no longer has the same airflow you would get by having the car move at high speed, and therefore the cooling efficiency drops immediately while the heat in the turbo is just starting to be evacuated.

I have another theory on why these cars seems to suffer so badly in a school environment. Let's say there's 4-5 sessions throughout the day. That means you're on track for 1/2 hour, off for about an hour to hour and a half, and then back on for another 1/2. While sitting in the pit with the car off, like most modern turbo designs the car/engine uses the coolant to cool off the red-hot turbo, so the heat continues to build up in the coolant and in an hour there's still plenty of residual heat in the coolant, and since there's no cool air flowing through the radiator there's no way to effectively evacuate the heat.

If anyone of you wants to try this, next time you go to the track, instead of shutting off the car immediately after you come in to the pit, drive around for 5 minutes with minimum boost (like cruising around the block at 2,000 RPM or something) to force both the radiator and the oil cooler to take a few more minutes to try and cool off the turbo. See if that will extend the thermal capacity of the system. And once you're parked, spray/mist some water on the radiator to help it evacuate heat (by vaporizing the water). I'm guessing that if my theory about the coolant acting as the cooling agent for the turbo once the car is shut off is why the coolant seems to trigger limp so often, this will go a very long way to stave off the problem in addition to upgraded oil and water cooling.

In fact, you guys may want to consider logging which session(s) limp mode comes on. If I'm correct, water temp triggered limp mode will likely come on during the later sessions, and especially if the schedule forces like a back to back session or only 1 session in between breaks.
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The hell I don't! LISTEN, KID! I've been hearing that crap ever since I was at UCLA. I'm out there busting my buns every night! Tell your old man to drag Walton and Lanier up and down the court for 48 minutes!

-Roger Murdock