I have had my new (to me) Z3 for about a month. '97, 2.8, 94 k miles. Passed inspection by a trusted BMW mechanic with no issues other than reccomendations for new pads (and rotors) and replacing the brake hoses with braided. No info on cooling system components other than a few obvious new hoses. Brake and cooling refresh, bushings are on the list for winter hiatus (New England). Temperure has been rock steady at 12 oclock (Iknow there is a deadband at 12 oclock so this does not mean actual temp is constant) for about 1000 miles of warm weather driving. Until today. Drove about 200 highway and fast 2 lane miles, about 55 f air temp and top down. When I turned the cabin heat on, max temp, fan 2-3) the engine coolant temp gauge dropped slowly to its 1/4 mark. Turn cabin heat off, coolant gauge rises slowly to normal. This behavior repeated every time I changed the heat settings.
I have never seen this behavior in any other BMW I have driven (2002, E36, E46) other than a stuck open thermostat that ultimately failed, but in that case the engine never warmed up and I had no heat. I am concerned that this is a sympton that I have never seen that is a precursor to a failure. Any input?
Dave
Definitely change the thermostat, it's stuck. The gauge on the cluster is buffered to stay in the middle for a broad range, so if it's dropping, your thermostat is sticking when it shouldn't be.
-Abel
- E36 328is ~210-220whp: Lots of Mods.
- 2000 Z3: Many Mods.
- 2003 VW Jetta TDI Manual 47-50mpg
- 1999 S52 Estoril M Coupe
- 2014 328d Wagon, self-tuned, 270hp/430ft-lbs
- 2019 M2 Competition, self-tuned, 504whp
- 2016 Mini Cooper S
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