Car overheats when I turn it off….

[5timesturbo]

While driving my temps are good but when at a standstill they go up but when I stop and turn it off….it full on overheats. I’ve checked for air in the system, and I believe the thermostat is good….. o JUST put this engine together and I’m trying to troubleshoot….what could be the issue at THIS point? Anybody have a diagram of how the coolant hoses around the back of the head should be routed?

[kojo96]

While driving my temps are good but when at a standstill they go up but when I stop and turn it off….it full on overheats. I’ve checked for air in the system, and I believe the thermostat is good….. o JUST put this engine together and I’m trying to troubleshoot….what could be the issue at THIS point? Anybody have a diagram of how the coolant hoses around the back of the head should be routed?

I wouldn't drive the car until you figure this out having just put the engine together. Full on overheats is subjective and could mean different things to different people. Go onto realoem, enter the last 7 digits of you vin and look at the cooling system diagrams. It'll help you "see" how the cooling hoses are laid out.
Also, bleeding these cooling systems can be tricky, thinking and knowing it's free of air are two completely different things.

[Mike W.]

Boiling over after shutdown used to be common, I fought it for a time on my first BMW, a Bavaria/E3. But now not so much. What you're running into is heat soak, it's right on the edge of overheating, but as long as it's running and the cooling system is working it's ok, but once you shut it off, the heat in the block and head continue to heat up the coolant and cause it to overheat. This is why many newer cars have electric fans that run after the engine is shut off, they continue to cool it when it's not running.

That's the why. What it sounds like from here is a bad fan clutch, possibly combined with either a plugged/restricted radiator and or a non op aux fan. The aux fan is funny, if the radiator is plugged, restricted, not completely blocked, what little coolant reaches the other side is now cool, because it take so long to get there. So the fan temp switches don't turn the fan on because the coolant on the cool side of the radiator is cool, but not enough is circulating to cool the engine.

Now it could be more or worse, but that's what it sounds like from here.

[1st 5er]

I'll vote for fan clutch at idle overheat.

Put an IR thermometer on your radiator, looking for cold spots, and also on the thermostat housing to compare to gauge.

[5timesturbo]

Well, I was coming today to give more info to see if it becomes more apparent what the issue could be. Here goes…. I removed the fan clutch from the water pump because I put a thicker aftermarket radiator and I didn’t have space for the fan clutch. However I did connect an electric fan to the front of the radiator that use a switch to turn and off…. It feels like a blockage in the system but I can’t see where. I removed the thermostat to see if that could be the blockage. It was not.

[turbodan]

If there is a blockage the radiator won't get very hot. This is not likely but easy enough to check out. If the radiator is getting hot and not cooling, as indicated by high outlet temperature, the fan isn't getting the job done.

The clutched fan can move a butt-load of air. You would be hard pressed to match that with most electric fans. The switch placement and temperature might need to be examined as well.

[Mike W.]

Dumb question, perhaps semantics, but you said you removed the stock engine fan and put an aftermarket electric in front of the radiator? You mean in front of the A/C condenser and removed the stock one? So you removed two stock parts and replaced them with one aftermarket? Clarification please.

[Shawn D.]

... when I stop and turn it off….it full on overheats...

You mean it boils over. How good is the condition of the cap, and how good is the condition of the lip the cap seals against?

[5timesturbo]

If there is a blockage the radiator won't get very hot. This is not likely but easy enough to check out. If the radiator is getting hot and not cooling, as indicated by high outlet temperature, the fan isn't getting the job done.

The clutched fan can move a butt-load of air. You would be hard pressed to match that with most electric fans. The switch placement and temperature might need to be examined as well.

I will check the radiator to see if it is getting hot. I would suspect it is because both upper and lower hoses seem to be getting hot.

Also, for now I have removed the ac condenser and placed the electric fan in front of the aftermarket radiator. I will at some point fix this because I do want to restore a/c to the car.


Yesterday I drove it and kept the fan on the entire time…, I still have not replaced the thermostat with a proper one(I cut the middle out to see if the thermostat was my blockage a few days ago). However, I did not over heat with the fan on the entire time and a little bit after I stopped.

[adam_poll]

What engine do you have?

The thermostat's in both M20 and M30 as they open actually close off another coolant passage to force the coolant through the rad. With the middle cut out who knows where the coolant is going, some through the rad, some (most?) bypassing it.

[K-jetFTW]

I'm with Kojo96 still, air needs to be 100% bled. And it still sounds like it's running hotter than it should ?

With 1) engine being apart 2) looking for cooling sys diagrams, maybe something got lost in translation.

Bleeding the heater core not complete ? You got good heat consistently ? Everything hooked up as per realoem diagram ?

Not trying to make you chase your tail, just looking at big things that changed, maybe related.

Best of luck.