BMW e30: Thermostat Replacement

Symptoms: Car is running cold, the temperature guage never goes all the way to 1/2 no matter how hard it’s run even on the hottest day.

Diagnosis: Probably the thermostat is stuck open, so the engine never has a chance to heat up properly. Coolant was being pumped in all the time, instead of only after the engine reaches the optimal 80C operating temperature.

Side Effects: High fuel usage since the car is always running rich and trying to get warm which will eventually foul up sensors, cat and other parts.

Drama!: I thought this would be a 30-minute job. Got up at 6AM to be less conspicuous, drained the coolant using the release valve at the bottom of the rad and removed the 3 bolts from the thermostat housing. I’ve done this before on an e30 at the Pick n’ Pull just to see what I’d be in for and it was pretty easy.

I stick the business end of my screwdriver under part of the thermostat’s armature to pry it out and the arm just peels right off! Uh-oh. A little prying later and… it’s really stuck! Either the housing has contracted around the thermostat or the gasket is so old it’s turned to epoxy.


See that photo? It shouldn’t look like that. Went to Home Depot, got a mallet and a cheap screwdriver and tried that combo on the edge of the thermostat: nope, not going to budge.

Times up, family is going out. We visited friends Nichole, Jonathan and their daughter for brunch. Watched Jonathan do a control arm replacement on his e30 M3 racer using liberal amounts of 4lb sledge hammer and with his encouragement decide this is the solution to my problem.

More Home Depot later I’m hammering away on the edge of the thermostat with the cheap screwdriver and the sledge (hopefully I didn’t knock too much crud loose into the engine). After 10 minutes I jam the screw driver into the thermostat, heave a few times and pop it loose.


Put the new thermostat in (which way is up? I’m not sure… I took a guess. The new thermostat (looks like I was actually shipped this one instead) doesn’t seem to have “up” marked with an arrow like the old ones) and started straining and refilling the system with the old coolant.

Car is no longer running cold, it’s now running a little hot so I must have an air bubble in the system. I’ll have to work on that by running the system + cabin heat and trying to bleed it out. But at least the car is back together and seems to be running.

Update: Topped up the reservior with distilled water then bled the coolant system of air last night then a little bit more today. Seems to be running at the right temperature now.


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August 6, 2012 Uncategorized