325i overheating replaced ex tank

[kathryn1956]

My 95 325i had a cracked expansion tank. I ordered a new one on special order no refund, when installing the plug was different, I used the inside core of the old ex tank with the correct plug and new expansion tank housing, all was well for a week of driving working in the field. It started to overheat on the freeway and I turned on the heater and it went to medium on my gauge. Called a shop who advised me there may just be air in system, did the bleed screw check, in fact each day for three days before driving. Yesterday when I used the air conditioner it began to overheat, did not overheat without air... I am going to the shop on Monday...any advice?

[Jeron]

Read the article in the Tech Info Center on bleeding.

Does the heater work?
Does it overheat while dring at 40mph or only when still?
Does you aux fan (the front most fan) come on with the AC?

[kathryn1956]

The heater works great. The car overheats when still when a/c is on and does not go down unless I turn on heater when moving again, then I quit using a/c and was fine. I did use the old coolant sensor as the plug in did not match my car. I will check the fan thanx for your input and help

[kathryn1956]

aux fan is on when a/c is on....

[Jeron]

The old sensor should not be a problem unless it is leaking around it. You can buy the plug part for the new sensor and when you do you should get a set of connectors, of which one should fit.

If it cools when moving I would say you either have air in the system or the primary fan (between the engine and rad) isn't working. Usually air in the system will cause no heat from the heater or sudden temp needle movement but I would still bleed the system as step one since you just did some work.

Read this: http://www.pelicanparts.com/bmw/techarticles/E36-Coolant_Flush/E36-Coolant-Flush.htm

Read I would bleed the system like the article states which should be about like this: get the engine warm, turn on the heater, opening bleed screw a bit and rev the engine. Coolant should flow out of the bleed screw with no bubbles.

You should have a mechanical primary fan and the clutch could be bad. Try using a small rolled up newspaper top stop fan while the engine is running. It should not stop or slow down noticeably.

However, I just went back and re-read your first post. You say that it only cools with the heater on. In that case I wonder if your thermostat is bad or stuck or clogged with debris. This prevents the coolant from circulating into the radiator so the only radiator you have is the heater core.

So to recap all my rambling...
1) bleed the system again just to be sure
2) check the primary fan with a newspaper because it is a simple test
3) you can try to check for circulation to the radiator by feeling the upper hose which should be very hot when the engine is warmed up. If you think it may be the thermostat the I would get a new thermostat, gasket, RTV and consider a metal thermostat housing while you are doing it.

[kathryn1956]

I appreciate your suggestions and will follow all of your instructions. I must add, the temp gauge goes to the normal warm position when I turn on the heater, once it is in the middle I turned off the heater and it stayed in the middle as long as I left the air conditioner off.... is this still perhaps a thermostat? I will do all tests, first bleed the system, the fan check and check the upper hose temp then for the thermostat I will have to take to the shop, and I will! I thank you so much for this forum and your site! I am learning so much!

[kathryn1956]

I want to thank you so very much for your advice. I am on the road again without overheating! It is hot here in Phoenix and I have my air working full time...no overheating. The bleeding was the answer! Thanks again! I am learning.