Thermostat - The Unofficial BMW M5 Messageboard (m5board.com)

tranck · 26th November 2008, 14:08

SES code idicated bad thermostat - water temp below 1st mark always except in stop and go traffic.

Having it replaced today - 1st one in 176,000 miles.

Question, does a bad thermostat affect performance?

I understand it would if the car was running hot but running cold?

Thanks as usual guys.

DouglasABaker · 26th November 2008, 15:40

It will, but more in the longer term due to water in the oil and excess carbon buildup in various places (not the same as the CBU issue talked about here) due to lower operating temperatures. From a hp perspective in the short term you might notice a small issue, but it won't be much - the engine will not make significant adjustments for being cooler than usual.

d-

Spooky36 · 26th November 2008, 17:34

I recently had this exact problem and ended up replacing the thermostat and temperature sensor. After driving for awhile with the problem, I did notice that while coasting with the car in gear I started to experience hiccups and hesitation. This did not happen with the throttle engaged, only while rolling with the car in (any) gear at low RPM's. Since replacing the thermostat the issue has disappeared.

On a side note, I ended up replacing the thermostat myself with the help of a friend in around 3 hours because the dealer wanted around $950 to replace it. The cost of parts (thermostat & sensor) was around $130. If you replace the O-rings and the thermostat housing gasket you're looking at around $180-$200 in parts. Just wanted to give you a baseline for the fix. PM me if you have any questions.