2002 530i runs rough in humid weather

[glj]

My wife drives it and assured me she has not run through big puddles. This only happens if it is raining so it's only very high humidity that causes it. It runs very rough and spews white smoke. If you try to drive it, assuming it continues to run, it has no power. My mechanic, who specializes in German cars and has always done a great job with the car, thinks it may be caused by a blown head gasket resulting from one time when the car overheated (not severely) after the plastic radiator tank cracked. He thinks it may be only 'moderately blown' but has not done a compression test. Yes, there is a little bit of coolant loss and a bit of brown goo on the dipstick that resembles an oil-and-water mixture. Whether he's right or not, I don't see how that could be affecting only high-humidity driving. The car starts and runs great the rest of the time. No missing at all and plenty of power.

[Jack Dabsy]

Does this happen when the engine is cold?
Is it pale brown, very light beige goo? If yes then H/Gasket...

[glj]

Yes, it happens when it's cold and yes, the goo is sorta beige. So that may confirm the head gasket diagnosis but would that explain the hard starting that ONLY occurs when it's very humid and no other time?

[Jack Dabsy]

Difficult starting when humid will just be a MAF issue I think, as the air quality is much denser and the sensor will be reluctant to give the correct signals to fire... Just my thoughts!!
Good luck with the H/gasket my friend ;-)

[glj]

Thanks. With good power and driveability and smooth idling - most of the time - I have to believe that if the head gasket is blown, it's surely a 'minor' blow. So for this, I've been told Bar's Leak Stop is worth a try, after I do a good flush. Your thoughts?

[Jack Dabsy]

Try a bottle of K-Seal... Short-term fix but I've had it in for nearly eleven months lol and no issues !!

[glj]

Good to know. Thanks, Dabsy