bmwe21.net forums

Hi,
I recently changed the thermostat on my M10 engine e21. No particular reason apart from the fact it was an easy & cheap thing to do and I was changing the radiator fluid anyway (I don't think it had been done for a while). The brand of the new thermostat is Mahle.

As you are aware the temp gauge on the facelifted e21 has 5 marks (or lines) creating four 'zones'. Previously the car consistently ran a bit over the middle mark into the third zone. After the thermostat change it now consistently runs a bit UNDER the middle mark in the second zone.

Is this all ok and expected? Or is my thermostat not quite right?

Cheers

The temperature gauge is rather sensitive in that specific area, so a few degrees difference might give another result, but nothing to worry about. Mine is a bit before the middle dash as well. It is worrying when it stays at the next whole dash before or after the middle.

Thanks for your comments - much appreciated

Totally agreeing with Wilmo, I would like to add the following from my experience :

When my car was all normal - and radiator working all right (normal meaning factory specs: thermostat 80 deg C, mechanical fan operating following engine turn) safe temp level was when the needle was staying from a bit before middle up to a bit over middle (max). When outside temp was normal and car was running on a free road with normal speeds, needle stayed a bit under the middle point ('dash'). At traffic (car idling for long) and/or very hot days and/or very spirited driving, or big loads, or driving uphill etc., the needle could climb a bit over the middle, but that would be all. When temp started climbing over than this it was time to inspect the system.

All the above, when after years I replaced factory specs thermostat by the 71 deg, started happening at half 'zone' less. I mean that normal temp was held a bit over the 2nd 'dash', and when things would get hotter, then the needle started climbing towards the middle.

Now with the custom made engine things are a bit more complicated, with combination of mechanical and electric fan etc. but I will not continue because it would be confusing.