Mystery coolant leak

[NotUrAvgM]

Im looking at purchasing a 99 M3 from a long time acquaintance and the car very slowly loses coolant. The cooling system has been pressure tested and only loses appreciable pressure after like an hour. Leakdown numbers are great hot and cold. Compression numbers are great. No visual evidence of coolant in the oil. Plugs and combustion chambers all look the same. No visible external leaks or smell of coolant. New radiator and cap. Stewart water pump. Only evidence of leakage is some occasional slight white crystallization around the radiator cap.

Thoughts?? At a loss on this one.

[RatedM3]

Maybe a hairline crack in the expansion tank? How about the heater core? I took mine out because it leaked.

[bennyfizzle]

Maybe a hairline crack in the expansion tank? How about the heater core? I took mine out because it leaked.

:rofl

[speedblind]

Mine did the same thing when I bought it - it turned out to be one of the 4-5 rubber hoses under the intake manifold. Pulled it off, replaced all of them and all better.

[autoxerwgn]

How much coolant are you losing and over what period of time? Are you sure it isn't normal consumption?

[NotUrAvgM]

Seller says about an inch on the expansion talk per month.

Is there such thing as "normal" consumption of coolant???

[CMG]

Coolant is not consumed unless there is a problem, no such thing as nomal coolant consumption.

[sh1ftgear]

I'm losing coolant about 1inch a month too. I recently redid my cooling system . changed radiator, thermostat, tstat housing, wwater pump and hoses. I dont see any visible leaks. Oil is clean as well. :help

[NotUrAvgM]

Coolant is not consumed unless there is a problem, no such thing as nomal coolant consumption.

Agreed

[RuninDawg]

Sh1ftgear

You may never see liquid with a very slow coolant loss. Look very carefully everywhere the coolant flows for telltale dried whitish residue.

Oh, hate to raise this flag, but don't forget about the possibility of leak from heater core or connections to and from the heater core.
I'm not saying I would go after the heater core, since it is a PIA, just raising the possibility.

And you say the oil is clean, but if you want to be complete, send an oil sample to Blackstone and see if they find coolant. I have seen cases without "brown shake" material on the oil cap and with normal looking oil on the dipstick that still had coolant in the oil. Presumably, the leak was so small that the heat from the hot oil was "evaporating" the coolant.

[sh1ftgear]

Sh1ftgear

You may never see liquid with a very slow coolant loss. Look very carefully everywhere the coolant flows for telltale dried whitish residue.

Oh, hate to raise this flag, but don't forget about the possibility of leak from heater core or connections to and from the heater core.
I'm not saying I would go after the heater core, since it is a PIA, just raising the possibility.

And you say the oil is clean, but if you want to be complete, send an oil sample to Blackstone and see if they find coolant. I have seen cases without "brown shake" material on the oil cap and with normal looking oil on the dipstick that still had coolant in the oil. Presumably, the leak was so small that the heat from the hot oil was "evaporating" the coolant.

Thanks for the advice! I actually remember now that I smell coolant when driving with the heater on. So it may be the heater core. Will check this weekend.

[chandlerseattle]

Thanks for the advice! I actually remember now that I smell coolant when driving with the heater on. So it may be the heater core. Will check this weekend.

Well gosh I'd look there first!

[AngelsNeverLose]

DIY of how to get to heater core?

[RatedM3]

Bently Manual is your friend. Invest in one. Otherwise, you can search for a bunch of informal ones scattered across the Internet.

[BMWManiac]

Getting the heater core requires removal of dash....not fun at all.

Another place to check is the heater valve that mounts on the firewall in the engine compartment. Take off the intake manifold and you'll see it.