Overheating

[Matto]

Other than thermostat and the radiator needing to be flushed what could cause overheating in my m20?

[FergU]

Water pump, clogged heater core, or heater core valve

[Matto]

Just changed my water pump and that wasnt the problem, so I guess that leaves the heater core.

[coupeowner]

Could be the fan clutch too. If it is heating up in stop-and-go traffic, but cooling at speed, I would suspect the fan clutch. If always heating up, most likely something in the coolant passages is blocked.

[M-technik-3]

Could be a dirty radiator also. Leaves and oil and dirt blocking fins.

[Jand3rson]

Could be the fan clutch too. If it is heating up in stop-and-go traffic, but cooling at speed, I would suspect the fan clutch.

That's EXACTLY what mine is doing. How do I test the fan clutch?

[M-technik-3]

Does it spin at start up and stay spinning? Next you roll up a big section of newspapers and stick into fan blades, if it stops then it's still good. But it needs to be done while engine is cool.

[Matto]

My radiator is fine, i just flushed it and i did the fan delete mod

[M-technik-3]

OK you did a fan delete and you have cooling issues? Now your confusing me. Did you add cooling capacity? or an electric fan. Orr why was your car overheating to start with?

[Jand3rson]

Does it spin at start up and stay spinning? Next you roll up a big section of newspapers and stick into fan blades, if it stops then it's still good. But it needs to be done while engine is cool.

If the fan STOPS then the fan clutch is still good? I was told the opposite before.

[e30Matt]

Does it spin at start up and stay spinning? Next you roll up a big section of newspapers and stick into fan blades, if it stops then it's still good. But it needs to be done while engine is cool.

If the fan STOPS then the fan clutch is still good? I was told the opposite before.

Yeah... if the fan STOPS your clutch is bad.

But rather than replacing the fan clutch, just buy a lower temp switch and delete it altogether.

I'm only running the aux fan and never see the needle approach the center mark.

[Matto]

OK you did a fan delete and you have cooling issues? Now your confusing me. Did you add cooling capacity? or an electric fan. Orr why was your car overheating to start with?

I added an electric fan.

[coupeowner]

Just to clarify. The newspaper test I know requires the engine to be warm (fan should be engaged) and if the newspaper can stop the fan, then it is faulty. It should be pushing a bunch of air. If it is weak, your fan clutch is slipping, and not providing the air movement it should.

[kansas-ix]

Small head gasket leak could be your problem, I just did my head gasket because I was having these same issues and the 3rd head bolt back on the intake side wasn't torqued correctly and was causing a small pressure leak forcing antifreeze out of the engine causing it to heat up. Once I get the car back from the shop (tranny work not the head-DIY) I did a nice paint job on the intake and valve cover I'll post.