Strange Coolant leak... can't find it!!

[Nightvelocity]

Hey Guys, it's been a loooooong time since I've posted here, a lot better than the old boards though. Anyhow, my 89' 535I is going crazy! My mom's been driving the car to work and a couple weeks ago the car overheated. My dad and I went out to pick the car up and try and drive it home and we didn't see any leaks. After starting the car I noticed some water dripping out from near the passenger side frame rail, initially I thought it was just the overflow hose dripping a little from the cap, but it was actually dripping from the side of the motor! Well my dad and I drove it home and about 3 minutes into the drive the car went right up to the HELLA HOT line and we could smell coolant burning off the exhaust manifold. We got it home and decided to replace the thermostat and gaskets because the lower radiator hose was ice cold. Well after replacing the thermostat the car ran perfect for about a week with no over-heating or any abnormal temperature fluxuations. Well my mom drove it to work and it overheated again. So the next morning when I went to pick her up from work and try to get the car home, it overheated again about 5 minutes from her job and about 10 minutes from home. Once again I noticed that coolant was leaking from the side of the engine. I thought maybe it was the head gasket but there is no oil in the water, or vice versa. I checked all the lines but couldn't find and leaks. Now here is the really weird part! The car sat in our driveway for about a week because we couldn't figure it out. Well last night we filled up the system, bled the air out of the coolant system and drove the car really hard for about 30 minutes and it didn't overheat and there was no leaks!!! WTF?!?!? I am seriously going nuts because my mom needs this car to get to work and I still like to drive it every once in a while. Does anyone know what the problem could be? I was thinking it might be the radiator cap, but it seems to be holding pressure. I doubt it's the heater core because the cab stays dry. Unfortunately it is so hard to see behind the engine from the top or bottom, that I can't see if there are any lines back there. Any help would seriously be appreciated guys!
Thank You!
-Tim
Tim@bulletproofautomotive.com
www.bulletproofautomotive.com

[Tiger]

Most likely heater hoses... most people forgets about them.

[632 Regal]

or head gasket failure, that would cause the engine to over heat with no load on it. Definetly check all the hoses very closly as mentioned but try it with the car at operating temperature where there is pressure. Make sure to use gloves and eye goggles, face mask etc, incase it is a hose about to rupture (disclaimer Do not do anything I say cause I said to) it has to be an obvious problem if it keeps occuring...know what I'm saying?

[winfred]

passinger side rear of the motor is the common failure point for the m30 head gasket, they machined a dip in the side of the head and didn't change the gasket to match the new footprint of the head, this makes a week spot and if the cooling system is not serviced often enough corrosion eats the gasket. the overheating comes from a air pocket forming at the thermostat keeping it cool and closed, after a few days of leaking it sucks some air and bam your screwed till you bleed it and refill. it's a easy head job, usually doesn't need any machine work unless it's been roasted bad and warped, if it's not making milkshake the head's probably fine

[632 Regal]

it's a easy head job


damn i should quit drinkin and go to bed but this is gettin fun!~

[Jeff N.]

Winfred's a wise man - but here's something cheap to check.

The reservior on the firewall can develop a crack between the black top and the translucent bottom. The crack will only bleed water when the car's hot and drip out near the aft of the motor. It could very well look like it's coming from teh back of the head.

Carefully inspect the tank, back of the firewall and the little support arm for signs of water & antifreeze. New tank's about $45 or so via BMA.

Jeff

[Nightvelocity]

Wow, thank you for all the quick replies! I am going to print out this page and just go down it like a checklist! :) I appreciate the help, I'll give you guys an update by sunday!
Thanx!
-Tim
Tim@bulletproofautomotive.com
www.bulletproofautomotive.com