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88 M3 Running Hot (archive)

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Posted by Chris Schrimsher on May 03, 2000 at 12:17:13:

Three weeks ago I purchased an 88 M3 with 57,000 miles from a friend. It's in pretty good condition however the temp gauge hovers between a little to the right of center up to
3/4's. This past weekend it even reached the red zone before I shut it down.

Here is what I have observed:
-Coolant in overflow tank is at mid point seam, or 1/2 full. I believe this is right where it should be.
-Coolant leaked a little three weeks ago but not any more.
-Driving with heater running keeps temp gauge in the normal, mid-point range.
-Turning on heater will immediately cause temp gauge to drop from about 3/4 down to the mid point.

I've read some of the threads on similar problems and yesterday evening I ran the car in the garage so that it would heat up. I was able to get the temp gauge just past 3/4's before I shut it down. I had to rev it a bit to get it this high otherwise it would have leveled off somewhere between 1/2 way and 3/4.

Here is what I've checked out:
-The auxiliary fan in front of the radiator NEVER ran but the one behind the radiator did.
-I carefully removed the pressure cap after shutting down and used a cooking thermometer to measure the temp. It was 170 F whereas the temp gauge below the tach read about 150 F.
-The cap hissed a bit as I removed it so I assume it's holding pressure ok.
-Both upper and lower hoses attached to the radiator were hot so I assume the thermostat is functioning and the radiator is not clogged.
-I assume the water pump is fine since it no longer leaks coolant.
-I checked ALL fuses and they looked ok.
-I manually rotated the auxiliary fan blades and they turned so it is not seized.

The Plan:
-Remove the auxiliary fan and have it tested. I assume this can be done, right? Replace if necessary.
-Flush radiator while it is out.
-Remove and test thermostat while radiator is out. Replace if necessary.
-Take a closer look at wires running from thermostat to make sure they are not brittle and broken.
-Flush entire cooling system.

-I'm troubled with the disparity between the temp of the coolant I measured with the cooking thermometer and what the temp gauge below the tach reads.
-Is it just the coolant is low?
-Will I be able to tell if the auxiliary fan is bad?
-Will I be able to tell if the radiator is clogged?

Am I missing anything?

Chris Schrimsher
[email protected]

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