E34 Overheating. No visible / Audible symptoms. HELP!!!

Hello fellow bmw owners. I own a 1995 525i with an automatic transmission and an m50 engine. the engine has 150k plus miles and had a previous owner before myself. My father and I, have come to what seems another obstacle in repairing my car.

(We had recently replaced the radiator and the thermostat. so those parts are good.)

Just a few days ago, on Wednesday my car without any real cue, overheated. I pulled over and popped open the hood. A faint spray of steam/vapor was burping from under the top portion of the engine. not the metallic side with the bmw logo on it but the opposite side the air intake. the next day, my father and myself inspected the engine and came the to the conclusion that aside from a broken hose, the fan clutch was not operating and needed to be replaced.

We ended up replacing not only the Fan clutch but also the water pump. after we had everything back in place we fired up the engine to test our work. I sat in the drivers seat keeping my eyes on the temperature gauge while my father toyed with the rev throttle on the top of the engine. For what seemed an eternity the tiny little needle would not go past the middle mark.My father continued to rev the engine; then slowly the temperature began to rise and rise and the needle went all the way into the red. We inspected everything that we had installed and nothing seems to be a miss. The temperature gauge along with the drivers console indicates that the car is overheating. the engine area, the radiator along with the fan clutch are all working and there are no visible / audible noises to show the engine is in fact overheating. The only thing that i'm suspicious of thus far is that when i turn on the heater no hot air comes out. The air that does come out is not even warm.
If you have any ideas of suggestions please be free with your thoughts and post them here. I'd greatly appreciate them.
Thank you for your time.

Did you bleed the air out of the radiator?

Open the bleed screw and fill the reservoir slowy to th ecold line, run the with the heater on and keep topping off till only coolant flows out of the bleed screw.

Now that i remember, no, I didnt bleed the radiator. I'll try that tomorrow and let you know if that solves the problem. thanks

+1 - Definitely part of your problem.

How frustrating! I'm feeling you on this one. I've begun to notice a similar issue on my 94 525iT. Have put the car on a hoist and looked at all hoses, have done a pressure test on the cooling system...but still coolant/water dissapears. Now the verdict is that I must have blown head gasket...making water/coolant enter my combustion system. This explains why I don't have any noticeable leaks.
Anyone have any idea how many workshop hours a head gasket job takes (if I send it to get done with my local BM specialist)???

Sounds like exactly what happened when my water pump decided to leave this earth. You changed that though. I agree with the air lock / bleeding theory. Hope that does it. Make sure you run the heat on, and listen for the auxilary pump to make sure it's working.

Wouldn't you see white exhaust smoke with a blown head gasket though? Blew on on a Volvo once, and had a nice happy white clowd following me.

i had a nightmare with a blown headgasket this winter and i'm afraid i had exactly the same symptoms as you hoodstalker, although i have an m20.
never figured out what caused it but the water pump was suspect.

exhaust from the head was getting into the coolant and you could see air bubbles in the coolant expansion tank and the coolant smelled a bit like gas.

i was stupid and went to someone i didn't know, i was kind of stuck it's a long story - http://www.bimmernut.com/forum/showthread.php?t=36378 http://www.bimmernut.com/forum/showthread.php?t=36488 quoted six hours labour and it took two ****ing weeks - hope you guys have better luck than i did.

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Originally Posted by hoodsstalker

Now that i remember, no, I didnt bleed the radiator. I'll try that tomorrow and let you know if that solves the problem. thanks

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Never get the air out if you dont. Be patient. May take a few attempts to get it all out. And mind you dont get scalded-steam may come out of that vent so dont unscrew it too far. Even when your heater does get hot watch that needle like a hawk. You sit in the car and let dad do the messing:D

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Originally Posted by Washburn

Wouldn't you see white exhaust smoke with a blown head gasket though?

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I thought so which is why i didn't think it was the hg at first. I looked for white smoke and I'm no expert but I didn't see any (it was really cold and i could have mistaken it for steam but i really don't think so) certainly not great big clouds of it - saw the hg after and it had definitely melted in a very small section. maybe exhaust was going into the coolant but coolant not getting into the engine? i don't know if that's possible - hopefully for you folks it's something else ... although i imagine with the right mechanic a hg job is not such a big deal as you'd think. please post what you find! - tim

edit: just to be clear on the symptoms i had - i had no heat at all at any time like you i think and the way you describe the engine temp guage moving (very slow to 12oclock then scary-fast to the red zone) is exactly what mine was doing. otherwise it ran normally or seemed to. good luck!

If the set up is similar to that of the 535i, make sure that the small vapour line from the top of the rad to the expansion tank is clear: this ~1/2" line can cause grief, especially prone to blockage at the small orfice where entering the tank on the firewall.