Coolant circulation issues

[AlexMaldonado]

So a while ago my car started to overheat when idling for long periods of time or when I was stuck in traffic so I decided to flush the radiator. After I got the old coolant out, I was only able to pour in about a half gallon of distilled water, and when I turned the car on to get it circulating, nothing happened. The water stayed and I let it idle until the temp gauge was will past the middle mark. I decided the water pump was probably bad so I went out and got a new one and just spent the night putting it in. They only issue is when I went to add the distilled water to finish the flush, it didn't circulate when I started the car either. I've got no idea what to do now or how to get this problem solved, so any and all help would be very useful. Thanks.

[TobyB]

You need to bleed the air out of the cooling system. I don't remember where
the bleed screw is on an m42E30- on the E36, it's on the top of the radiator.
Google will show you.

Then you need to fix your fan(s)- the clutch is probably not working, if you only
overheat after idling a while.

hth
t

[bmwman91]

The bleed screw is on the radiator next to the fill cap. Do NOT overtighten it. If you do, you will either strip it or crack the plastic housing, meaning a leak, which you have to replace the radiator to fix.

On a properly maintained M42 coolant system, bleeding is a super simple 60 second process...fill the coolant, start the engine with the bleed screw open, let it run / rev it to ~2500RPM and add coolant as needed while air escapes to keep the level at the right spot. Close the screw when no more air escapes.

Bleeding is a bit more work on an M42 with a crusty coolant system since the air bypass groove gets clogged up. In that case, you have to park the car on an uphill incline, the steeper the better, and run it until the engine warms up enough to open the thermostat. This is sort of a problem if there are large air bubbles in the head since you can get hot spots, and you probably need to rev it up a bit more to push the air out.

The air bleed bypass is in the metal thermostat housing. You will see a small groove connecting the 2 chambers. It should be clear and open, but it is often plugged with various "stop leak" crap, RTV, calcium deposits and that sort of thing.

[c0rbin9]

You may have a sticky thermostat that isn't opening completely.

I had the same issue as you with my M42 even after replacing the fan clutch, I did a complete block/rad flush, changed the thermostat, and the issue was solved.