Quote:
Originally Posted by j.fro
Here's my experience on the same question; looking forward to input. I've got the Dash Command app and the elm wifi transmitter. In my 1999 996 C4 on 95+ degree days I'll see coolant temps stabilize around 216 running 71 on the highway. In highway traffic accelerating/decelerating, temps get to 221, but no higher. On cooler days, temps never get that high.
How hot is too hot?? 225? 235? 245? 250?
FWIW, my 986S with center radiator and hood vents never gets over 219, and cools down to 180 quickly once we're moving.
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OK, here's the problem: When the overall temp is 216F, there are parts of the engine that are hotter, and some that are cooler. That differential is not particularly good for an alloy cased engine, and the thermal loading contributes to things like cylinder head cracking.
Secondly, if the coolant is at 216F, the oil is probably near 230F, which both shortens its life expectancy as well as reduces its ability to cool the bearing surfaces (one of the principal functions of oil).