99 540i 6speed.
Few days ago I noticed my coolant temp hovering lower than usual, in the low 90C. My car topically operates around the 104 -107C range, a bit higher if in traffic. The highest I’ve seen it is at 110. So when I saw the lower temperature readings on the coolant I was pleasantly surprised. This only lasted for two or three days and now it is back to normal temperature range. I monitor coolant temp on the cluster menu, #7.
Could this be a sign of my thermostat or temperature sensor going bad? I think maybe it was stuck open for a few days and that’s when it was showing the lower operating temperatures. My new cheap scanner says this.
C4B160FE-ADE5-4621-8B5E-2D48D2018031.jpg
My thermostat went bad a couple of years after I bought the car new. The temp gauge would only get to around 11 o'clock and the heat from the vents was lukewarm. At the time I didn't know how to use test 7 to check the coolant temps so I have no idea just how low the temps were.
2000 528i sport
EMP Stewart water pump
Dice iPod adapter
Alpine amplifiers
MB Quart speakers
MTX BGE12 subwoofer
AudioControl EQL equalizer
Bad 'stat is my guess.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.
Yeah the thermostat is probably bad. How long does it take for the car to reach operating temperature (temp needle in the middle of gauge) from a dead-cold start in the morning?
If the warm-up time is unusually long like it was on our X5 in this video, its probably a stuck thermostat. Really common, even on our X5 where the t-stat was only a few years old.
Not a V8 E39, but the concept is the same, hope it helps:
link: https://youtu.be/JAR7UDSDUew
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