overheated M20 - what to check for?

[mspiegle]

I didn't think this fit in the M20 Stroker/FI forum, so posting here...


I have a somewhat low mileage motor (120k) from a '90IS that was overheated pretty bad. I'd like to humor myself and make sure the engine is trashed before I get rid of it. I plan to pull the head off, check to see if its straight, check the headgasket, and do a compression test. Is there anything else I could check while i'm in there? I haven't drained the oil yet either... its M1 15-50.

[AdamF 88iS]

There is a HUGE chance that the head is cracked. Check that first before you spend any money on it.

[T.Dot E30]

After it overheated, how does it run?
Just bcus it overheated doesn't mean its done for, there is still a slight chance nothing happened, or that it can be fixed instead of swapping out the motor.
Is it leaking coolant?
Is the coolant mixing with the oil?
Is the engine knocking?


I've seen m20s run fine for a while before showing any signs of damage, but ya it does depend on how bad it did overheat.

[mspiegle]

The car hasn't been started since the incident. Before the car was shutdown, it was running on the freeway at 70mph with no coolant and pinging with anything more than 1/2 throttle.

I know for a fact that the headgasket is busted. In fact, I think that's what ended up causing the car to overheat and spew coolant. I'm certain there's coolant in the oil and vise versa.

I'd bet $20 the head is probably toast, but it would be nice if the block were still usable. I'm totally prepared to just buy another motor, but if I can get away with just another head... that would let me spend some money on other mods.

Is crack inspection a relatively easy visual thing, or would I need to strip it down and have it hot-tanked so I can see better?

[AdamF 88iS]

M20 head gaskets don't usually go out by themselves. The head was probably the problem in the first place.

Sometimes you can see the crack visually, but having a machine shop do a presssure test would be ideal.