Antifreeze mystery

[m3f_98M3csm]

Well every couple months my M3 is missing enough coolant to cause the OBC to tell me to check it. It passed a compression check recently ranging from 173 to 183 psi. Soot in exhaust pipes appears normal black. I keep the car garaged and have found no coolant drips. Where is it going?



Thanks.

[m3f_EM3DRMZ]

Might have a pin hole in the expansion tank. Happened to mine and the coolant would evaporate quickly if it was a small amount.

[m3f_JCinRI]

I always have a spare cap for the expansion tank in my spares box. They fail on a regular basis.

[m3f_badgtho]

How old is your cooling system? Do you have a plastic thermostat housing? If not, what brand is your metal one?


The most likely culprits are the thermostat housing, radiator seams, expansion tank, level sensor.

[m3f_Anubis]

As a side note: if your car has over ~70,000 miles and has never had a full cooling system replacement (expansion tank, coolant level sensor, t-stat, water pump, hoses, radiator), you should do one. Expansion tanks are notorious for cracking, as are the plastic necks on the radiators. T-stats get stuck, water pumps break and fail, and hoses crack and leak. Basically, the entire E36 cooling system is a disaster. Replace it all.

[m3f_ECS Tuning]

BMW coolant leaves white residue when it dries. I'd start by hunting around the engine bay looking for residual.

[m3f_Jrrrrrrr]

A coolant leak slow enough to only drop a few ounces per day may not leave any drips on the ground, and possible minimal residue depending on where the leak is. My guess is the you're only leaking when the system is under operating pressure - IE while running and shortly after shutting the engine off.



As such, obviously look for residue first, but don't be surprised if you don't find any. Rent, buy, or DIY cobble together with an old expansion tank cap and compressed air nipple, a cooling-system pressure tester to find or confirm the leak.

[m3f_stack]

Perhaps it is a coolant leak that only happens at certain times.


For instance temperature.


Leave the car running for a long period of time.


Maybe it happens when it cold/hot.


Hard to say. Look for white residue as mentioned above.

[m3f_Richardsperry]

If it's leaking enough to require adding more, it WILL leave a trail if it's a leak. If it's burning it, not so much.

[m3f_98M3csm]

Thanks guys. Guess I'll look into all of that.