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.

[kayger12]

Ok. Expansion tank should still be good. Not saying it couldn't be the issue, just not likely. Cap could be the issue if they reused the old one. I'm still thinking water pump if it hasn't been replaced...

[johnnye23]

It may be worth some piece of mind to buy a pressure tester from harbor freight and pressurize your cooling system. It will aid I'm locating a leak that occurs only under pressure.

[spencers]

Could be the radiator... They're known to go out at 200k; mine did.

[Ryans323i]

It may be worth some piece of mind to buy a pressure tester from harbor freight and pressurize your cooling system. It will aid I'm locating a leak that occurs only under pressure.

This might be something to do.

Isn't the system pressurized when the car is running/idling? Does the car have to be at a certain temp?

[MrMaico]

This might be something to do.

Isn't the system pressurized when the car is running/idling? Does the car have to be at a certain temp?

No, not really pressurized at normal operating temp. Here's a video I made to shut up some of the so called experts on another forum last summer that were basically telling people they would burn their face off if they opened the cap when hot. It's hard to even hear the pressure release. This was after driving for about 1 hour and you can see the air temp was 86.


http://www.youtube.com/watch?v=9Hi6Z6RZgIc

[mimalmo]

Not to mention you can run the car for a while with the cap off.

[billschusteriv]

You said no signs of leakage? Nothing by the cap or underside of the hood?


It may be worth some piece of mind to buy a pressure tester from harbor freight and pressurize your cooling system. It will aid I'm locating a leak that occurs only under pressure.

My mechanic did this on my e46 and wasn't able to find any issue until he:

Attached the pressure tester
Ran the car at idle
Routed the pressure tester/gage under the hood to the drivers compartment
Closed/bungied the hood
Drove the car down the street

My old engine was pressurizing the coolant system at power and causing the cap to relieve pressure under the hood.

[Ryans323i]

No, not really pressurized at normal operating temp. Here's a video I made to shut up some of the so called experts on another forum last summer that were basically telling people they would burn their face off if they opened the cap when hot. It's hard to even hear the pressure release. This was after driving for about 1 hour and you can see the air temp was 86.

I did not know that! I really thought it would gush out. I heard your V1 at start up, btw, nice.


You said no signs of leakage? Nothing by the cap or underside of the hood?



My mechanic did this on my e46 and wasn't able to find any issue until he:

Attached the pressure tester
Ran the car at idle
Routed the pressure tester/gage under the hood to the drivers compartment
Closed/bungied the hood
Drove the car down the street

My old engine was pressurizing the coolant system at power and causing the cap to relieve pressure under the hood.

There's no obvious leaks (looking from above with a flash light). I need to get in there and look a little better. I meant to look while the car was in the air this past weekend, but I didn't get to it.

Thanks for all the input guys.

[billschusteriv]

Sometimes these leaks are really hard to track. I still haven't found where the coolant is going in the e30. Nothing from the e30 or e46 ever made it into the oil. So I'm thinking it went elsewhere.

Good luck...

[mikeyb74]

Is your e46 auto or manual? Sorry I have to ask. There are two hoses under the expansion tank on auto equipped cars that will leak. I ended up replacing both of them. Or could be the bracket the expansion tank mounts to on automatics.

Also I went thru 4 expansion tanks in 6 months. All but one was cracked down the side. The 4th one gave out where the top is mated to the tank. My indie told me it was from over pressurizing the system.

[Ryans323i]

It's a manual. I've been hearing a lot of stories about the expansion tanks. I'll be paying extra close attention when I get in there.

[llll1l1ll]

Sorry to revive and subsequently hijack this thread, but is there a way to check the water pump weep hole while the vehicle is running?