I have an odd situation with the cooling system in my 924S. When the outdoor ambient temperature gets colder, my car runs hotter.

In the middle of summer when it's 100 degrees outside, my car will run all day with the temp gauge right on the halfway mark, only rising when I'm sitting in traffic. But whenever the outside temp drops below 50-60 or so, the needle will start creeping upward even when I'm cruising along at 60mph. It'll usually hang around the 3/4 mark, and if I turn on the heat, it'll start climbing even higher. That scares the hell out of me, so I'll turn off the heat and it'll ease back down to the 3/4 mark.

In the five years I've owned the car, it's always run a little hotter during cold weather, but during the first few chilly nights of this year, it seems to be a bit worse than it has been.

Nearly everything in the cooling system is nearly new: T-stat, radiator, heater control valve, coolant flushed and bled. The water pump will be due next summer, but other than that, I'm clueless.

Any thoughts?

 

temp sender in the head or the gauge?

Have you verified via IR thermometer that teh engine is actually hotter, and matching the gauge indication?

 

the same happened to me just this morning. it got worse as i turned up the heat and backed down a little after turning it off. the guage was acting a little wonky (would read high, then bounce a bit, then go back down, then go back up and light up the dash). i know the fans are working but i'm at work and don't have time for further diagnostics.

 

JKW, I took your advice and "borrowed" an IR thermometer from work, and I found some interesting information. While I'm getting the same gauge/sensor relationship whether it's a cold night or warm day, I'm only getting a reading of 185F when the gauge is reading 3/4. Clark's Garage says that the 3/4 mark on an early gauge should be 207F. So I'm wondering if I'm actually running cooler than I think I am all the time, and when it seems to be overheating in cold weather, it's actually running about where it should be.

I took my readings from the cylinder head, right where the temp gauge sensor mounts. Would this be a somewhat accurate reading of what the water temp is?