Cooling System Help & Advice Needed

[vrracr]

Hi All,

I'm perplexed by overheating issues on my M20 and I'm hoping someone here can guide me.

The car overheated on me last month and since all of the components were original anyway, I decided to spend the time and money to update them. I replaced the thermostat, water pump, many hoses, expansion tank, coolant cap and even changed the head gasket. Then I flushed the system and got a lot of gunk out of the radiator. To my disappointment, this seems to have made the overheating issues worse. Yesterday, I tested engine compression and got great compression on all 6 cylinders, so I know that's not the issue.

Once the car warms up, the coolant spews out of the expansion tank. With the heater on, the car doesn't overheat. With the a/c on, it overheats quickly. With the a/c off, it does overheat, but takes much longer.

Another thing I noticed is that the lower hose coming from the radiator stays cold, while all others get very hot. This would lead me to believe that perhaps the radiator is the issue, but I took it out and flushed it again and water flows freely through it and it does not leak coolant (at least from what I can see) when the car is running. The fans work fine.

Any help would be greatly appreciated because I'm stumped!

[Mook613]

Sounds like you have a nice air bubble. Need to bleed it well to ensure all the air is out.

[wilholl]

!!VERY IMPORTANT!!

Make sure that the little bleed hose connected to the top of the radiator and the top of the expansion tank is NOT blocked, obstructed or plugged!

If this hose is plugged, there will be air trapped in the cooling system and this will cause conditions exactly like you are experiencing.

This comes from experience... i just went through this very same thing with my e30. I replaced everything first and was convinced that I had a bad head gasket.
Luckily, I checked the bleed hose just before tearing the engine apart.
Replaced hose and blew out the port at the expansion tank and now driving happy...