1999 BMW Z3 heating problem

Hey guys new to the site, it's been awesome so far. Question I have a 1999 BMW Z3 2.8l coupe, while driving I noticed the heat started blowing out cool air. I was told to check the coolant expansion tank cap and make sure it was tight. I replaced cap and filled the expansion tank with Anti-freeze. I drove the car approximately 7 miles and the heat started blowing hot and a short time later it started blowing cool air. I noticed smoke coming from the coolant expansion tank area. The temp hand never moved and or did the vehicle indicate any overheating. when i looked at the coolant level in the expansion tank again it was low. I did notice a leak from the small pressure relase valve on top of the coolant tank. I also think that coolant tricled down to the headers. I re-filled the coolant tank and the heat is working. Any suggestions on the cause of this problem?

Assuming that all the components of the cooling system are in good working order, you have the text-book symptom of air in the system. When the cooling system is purged of ALL air, you should get a stready flow of REALLY HOT air from the duct vent

Refill the expansion tank, loosen the vent screw next to the cap, and run the motor until only coolant without air escapes from that vent. Top off the expansion tank and cap it off. Enjoy heat! Also, once up to temp and pressure make sure that there's no leak from the expansion tank - they tend to crack with age. Ask me how I know.

To continue (not sure how that "posted itself" before I was finished with it...):

The Z3, and all late model BMW cooling systems, unfortunately, is made largely of plastic components. Plastic that is subjected to constant temerature extremes. Need I say more?

If the cooling system fails and the engine is not immediately shut down, warping the aluminum cylinder head is probable.

The easiest way to bleed the cooling system is using this Air Lift II device, it pulls a vacuum on the system, then draws in the coolant, minus the air:

I work on Z3s, mostly ///M Coupes & Rdstrs, exclusively, so I've got a pretty good handle on what makes these cars tick. My online gallery has over 26,000 pictures, probably 80% of work I've done on ///M Coupes/Rdstrs: www.spcarsplus.com/gallery3

Thanks guys that helps out alott, I have a good starting point. I will keep you informed.

A lot of BMW guys (myself included) consider the whole cooling system basically a maintenance item; mine gets completely replaced every 100k miles. All that plastic is failure-prone, and if you piecemeal it it's just one thing after another. Given the very real danger of expensive engine damage with an aluminum head or and all-aluminum engine, it's relatively cheap insurance.

I've got a 2007 3-series. Are the cooling systems on those cars mostly plastic as well? From what I recall it does at least have a metal impeller in the water pump now.

Xceler8x wrote: I've got a 2007 3-series. Are the cooling systems on those cars mostly plastic as well? From what I recall it does at least have a metal impeller in the water pump now.

Oh yeah. The water pump impeller problem seems to have been mostly resolved, but everything else still degrades. When I did mine, I replaced radiator, expansion tank, pressure cap, hoses, thermostat, water pump, fan clutch, and bleed screws (get the brass ones; the plastic ones are very fragile). Flush and refill with proper phosphate-free coolant and you're good for another 100k miles (maybe 80k if you've got a V8 or very tightly packaged I6, as these have higher underhood temps).

suzukirfboy - there is no doubt that you have a coolant leak. If you're not comfortable diagnosing the source & making the repair yourself, take it to a repair shop ASAP - it only takes a couple of minutes of low coolant to destroy one of these engines. By the time you notice the temp gauge spike, it may already be too late.

02Pilot wrote:

Xceler8x wrote: I've got a 2007 3-series. Are the cooling systems on those cars mostly plastic as well? From what I recall it does at least have a metal impeller in the water pump now.

Oh yeah. The water pump impeller problem seems to have been mostly resolved, but everything else still degrades. When I did mine, I replaced radiator, expansion tank, pressure cap, hoses, thermostat, water pump, fan clutch, and bleed screws (get the brass ones; the plastic ones are very fragile). Flush and refill with proper phosphate-free coolant and you're good for another 100k miles (maybe 80k if you've got a V8 or very tightly packaged I6, as these have higher underhood temps).

Thanks for the tip! I'll keep this in mind..