Hello everyone,
I picked up a 2003.5 M3 in Montana in October 2024. One thing I immediately noticed was that occasionally the temperature needle would drop from dead center when I was cruising off throttle or going downhill. Car has 80k miles and sat quite a bit the last decade.
When I got home, I replaced the thermostat with a new Wahler. I boil tested it both it and the original thermostat, and noticed that the new one seemed to open at a higher temperature and quicker. I thought – “aha got it!”
Well it still does this some. Tonight I hooked up an OBDII scanner and found out the gauge will drop below 12 o’clock if the coolant temperature falls below 83° C. The first little dot below the mid-point is at around 73° C FWIW.
Cruising uphill on the highway, I’m at around 91° C. Car warms up quickly. If I get off the gas and cruise, my radiator outlet temperature drops quickly and the engine coolant will drop temperature to around 82-83 or so before it stabilizes and then the outlet temp drops rapidly. I assume this all a result of the 80° C thermostat closing. This seems good to me?
However, if I keep cruising temperature will slowly drop. I saw as low as 79° C going downhill on a frontage road off I-40 through the Sandia's for a few miles. This causes the gauge to start start dropping as I've seen most times I drive the car.
Coming from m/s52 and m54 engines where the needle absolutely doesn’t move from center unless there is a problem this is disconcerting. However, given it’s an 80 ° C thermostat and any coolant temp below 83° C causes the needle to move, it doesn’t sound nutsy to me to think that the S54 “just does this” because the gauge is less buffered.
Is this normal S54 behavior that is well known (cause race engine?) or do I have a potential problem here? Thanks!
I picked up a 2003.5 M3 in Montana in October 2024. One thing I immediately noticed was that occasionally the temperature needle would drop from dead center when I was cruising off throttle or going downhill. Car has 80k miles and sat quite a bit the last decade.
When I got home, I replaced the thermostat with a new Wahler. I boil tested it both it and the original thermostat, and noticed that the new one seemed to open at a higher temperature and quicker. I thought – “aha got it!”
Well it still does this some. Tonight I hooked up an OBDII scanner and found out the gauge will drop below 12 o’clock if the coolant temperature falls below 83° C. The first little dot below the mid-point is at around 73° C FWIW.
Cruising uphill on the highway, I’m at around 91° C. Car warms up quickly. If I get off the gas and cruise, my radiator outlet temperature drops quickly and the engine coolant will drop temperature to around 82-83 or so before it stabilizes and then the outlet temp drops rapidly. I assume this all a result of the 80° C thermostat closing. This seems good to me?
However, if I keep cruising temperature will slowly drop. I saw as low as 79° C going downhill on a frontage road off I-40 through the Sandia's for a few miles. This causes the gauge to start start dropping as I've seen most times I drive the car.
Coming from m/s52 and m54 engines where the needle absolutely doesn’t move from center unless there is a problem this is disconcerting. However, given it’s an 80 ° C thermostat and any coolant temp below 83° C causes the needle to move, it doesn’t sound nutsy to me to think that the S54 “just does this” because the gauge is less buffered.
Is this normal S54 behavior that is well known (cause race engine?) or do I have a potential problem here? Thanks!
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