Losing coolant.

[Ryans323i]

I'm losing coolant, and I can't find the leak.

About two years ago, summer '08 (I believe) & 160K miles, I overheated and blew the expansion tank. This was before I was a DIY'er (and the main push into DIYing) and I sent the car to my local BMW dealer for the cooling system overhaul. The overheating was caused by my non-functioning fan, so that was replaced, along with some hoses, expansion tank and new coolant.

A few weeks ago, I was checking my fluids (like I do often, but usually on check the coolant 1/year) and my reservoir was nearly empty! I filled it up, ran the car, and the level stayed up. Two weeks later, I check it again, and the reservoir is 1/4 low (the bobber was in the lowest position). Filled it, went for a spirited drive, and the fluid level was fine when I got home.

Today, two weeks later, I check it again. I'm a 1/4 low again. There's no puddles under the car, the temp gauge is not creeping over noon, where in the hell is my fluid going?

The car is running great, so no blown head gasket, IMO. When I overheated and blew the expansion tank I was at a drive thru and was able to immediately turn off the car. BMW did a check for any damages incurred, and they said everything was fine. Today, I did a quick check of the obvious coolant hoses, and they're dry.

I'm a little nervous, I've got a trip planned to Charlotte this weekend (2hrs away) and I don't want any problems.

[mimalmo]

Buy a jug of the BMW coolant and couple gallons of the distilled water. Have it pre-mixed and ready to go for your trip. It's cheap peace of mind.

BTW: check the weep hole on your water pump.

[kayger12]

+1 on the water pump. Tough to find coolant leaks sometimes because some leaks only show when the system is pressurized.

Check the radiator drain plug and the coolant temp sensor for leaks as well.

Is it the original radiator?

[kpro]

Ryan, my car is the same way. I have a weepy hole on the water pump, but its never wet and nothing else is either. I add coolant once a month it seems like. BMW told me it was normal :/

[Ryans323i]

I can't remember if they changes the radiator or not. I know they didn't change the water pump. I'll look over my receipt again and see.

That sucks that this could be "normal".

[nk_zhp]

Expansion tank caps are not an uncommon place for leaks because they have built in pressure relive mechanism, that, when failing, releases coolant vapor prematurely.

It might be worth replacing. or at least watching when the system is fully pressurized, for hissing noise.

[Matt]

I had a hairline crack in my expansion tank that I was unable to locate until I removed the airbox. It was at the way bottom corner, and provided me with the same symptoms you are having.

My guess would be that there is a big enough leak to slowly drain the coolant, but small enough to not make puddles (and be extremely aggravating in the meantime). Problem is, there are a bunch of places that this type of leak could occur. What helped me find my leak is I had/have bright green coolant, and it really glows under a LED shop light. I wouldn't have found it otherwise. Good luck, though.

[static667]

Be sure to keep a close eye on it and take some extra coolant. I had a similar issue with my '94. Turned out to be a cracked expansion tank.

Edit: It was, however, a hair line crack. The leak was barely noticeable.

Sent from my rooted Fascinate. Hacked Droid FTW!

[kayger12]

Ryan-- how many miles since you had the coolant overhaul done?

[Ryans323i]

Im at almost 193K, so around 30k.