Overheating troubles

[Liquidvash]

Original problem:
Car overheated while idling. Aux fan would not come on. Radiator only got hot on the drivers side. Car had heat inside.

This is what I have done:
- NEW Thermostat (heated to make sure it works)
- NEW Water Pump (and tbelt and tensioner while I was there)
- NEW Radiator (mine was chock full of rusty goodness)
- Jumped & checked the aux fan - the fan only works on high - my resistor is bad - have not replaced it yet (it's a Magna).
- Jumped the aux fan (for now) on high speed so that it is always on
- Flushed and filled
- Bled the system on an even surface

Current status of my overheating:
After flushing the rad (not the block... forgot to do that), and bleeding the system using the bleeder screw, with the aux fan always on high - car still heats up to 3/4. Does not go above that, but does not go to 1/2 either. When I open the bleeder screw and rev the car to 1500~ RPM the heat goes down to almost halfway between 1/2 and 3/4... but never lower. Car still has heat inside of the car... even better heat now that the rad has been replaced.

Note: After replacing the rad, it still only gets hot on the drivers side.

My theories:
I'm thinking of trying to flush the system again, this time flushing the engine block as well. Filling, and then trying to bleed the system on an incline instead of on a flat surface like I have been doing. After a lot of post digging I read that this could help bleed the system better.

Questions:
- When the car is idling at normal speed (800~900RPM) should there be coolant coming out of the bleeder screw?
- Should all of the radiator get hot when the car is hot?
- Should I check the lower hose on the rad (pass side) and should that hose be hot or cold?
- Visual inspection of the lower hose seemed like it was in good shape... but how can I really tell?
- Does anyone have a good diagram of the coolant system flow for 88+ m20 engines (coolant tank on drivers side)? The Bentley only has the older system (pre-88) and it confuses me when I look at it.

Thanks for all your help!! :)

[E30Classic]

I had the same problem after replacing all the same parts. See link. Then I drained the block too, and rebled, and rebled. Now it seems to be better, with the coolant circulating (pass side of radiator gets hot too as does the lower hose - not as hot as the driver side, but slightly cooler).

My problem, or maybe it's not a problem, is that the hoses feel swollen, like there's too much pressure. How are yours?

[CorvallisBMW]

First off, check the resistance on your temp sensor. It may be that you are not running hot, just getting the wrong signal from the sensor. It's not common, but I've seen it happen before. If it checks out to the proper resistance, I would flush the whole system (block included) and bleed on an incline as you described.

[jlevie]

With the parts you've replaced, overheating at idle will be from air in the cooling system or a bad fan clutch. The procedure I use for bleeding an engine is:

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500 for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

Test the fan clutch by dragging a rolled up newspaper against the blade tips while the engine is idling. With a cold radiator the fan should be easy to stop. With the radiator hot it should be difficult to stop.

The aux fan problem is a red herring. It is only there for additional cooling when A/C is in use an the car is stopped or at very low speed. The engine fan is more than capable of providing all cooling necessary if the A/C is off.