1996 BMW 328 check engine light, Air pump had water in it

TRAVSBMW

MEMBER
1996 BMW 328

1996 BMW 328 Automatic 140000 miles

My son had a 1996 bmw 328. Check eng light was on, needed to get smog checlk.

went to repair guy, he found brown water/rust? Was in the air punp and filter was wet and filthy. He replaced the air pump (part $275). Check eng light is now off. But, he didnt know why water was in it, my concern was if he doesnt kmow why water is there, then what stops water from reappearing. And can that redamage the newly replaced pump/filter?

he said he could check (dont know part name, but it is about a foot away from filter, down the ridged hose ( smaller black round unit about 3" in diameter).

left the car with him to replace unrelated item. Where do you thinik the moisture would come from? And once it is fixed, how many miles required to smog check with a smog check only facility on a bmw? I have been told from 20 miles to 150 miles from 4 diff people
thanks

3 Replies

JAMES W.

MECHANIC
2,394 POSTS

The water in a smog pump is from condensation from the warm air passing through it. It's the same principle as carrying a cold piece of steel into a warm house and the moisture in the air instantly condenses on the steel. If the diverter valve is not functioning (which I believe is the little round thing you're replacing) the pump moves more air which leads to more condensation. Remedy, periodically add just a little bit of isopropal alcohol to pump inlet. This will absorb what little moisture is trapped in the pump. By periodically, every 3 or 4 months especially in the summer months when the air is more humid.
As far as how far to drive before a smog test. 10 to 20 highway miles should be plenty. You want the engine to be well into operating temp.
Hope this helps.