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dsheetz
12-08-2011, 06:34 AM
Ok, i need some help. My 90 535I suddenly has no heat and the temperature gage is fluctuating from the middle (where it has always been steady) to the hot reading and back. Also the computer is telling me to check the coolant levels. The coolant is full. Has my thermostat gone bad and if so, is it a difficult procedure to replace?

Thanks in advance for any thoughts!!
DSheetz

InfiniteDice
12-08-2011, 08:36 AM
1) Probably siezed thermostat, when the car is up to temp the read should be too hot to touch near the inlet, and very warm on the rad outlet. You may need to remove the fan and shrould to test. DON'T chop your fingers off. Another way to tell is the outlet hose from the rad should be warm, if it's cold then there is no coolant getting through the rad.

2) The coolant temp gauge can go wonky when the temperature starts exceeding the normal levels, I'd say the temp is slightly over the middle range. Knock on the cluster to see if that helps, it could be a loose ground screw.

3) The coolant wiring may have a short or the actual coolant level sender is shot, test by taking the sender out of the tank and moving the floater by hand. Put the floater in a high position then turn the car on and check the coolant low light. Turn key completely off and do the same thing with the floater on the sender in the lowest position.

The thermostat isn't hard, the biggest issue will be corroded bolts, get the thing hot then loosen them just so they move, that should help a bit. Make sure you get a new housing seal and I'd suggest getting a new coolant bleed screw (coat the threads with anti-seize). You can find the procedure online. If you don't use a manual make sure you take note of the arrow on your original thermostat, you need to position the new one EXACTLY in it's proper orientation or you'll likely have issues.

Good luck.!