My engine got hotter than the sun

[stoatmax]

I'll try and keep it short. Basically I bought a 91 SHO in LA a few weeks back. Ran great, sounded great, looked great. Was 30-45 minutes into the trip when out of nowhere, the car started losing power. Crap.
We pop the hood and the radiator cap had blown off. Valve covers instantly boiled our spit. It wasn't a pretty sight.

Fast forward to today, and I've ordered all the 60k components, rod bearings, head gasket, as well as taken the heads from my buddy's SHO engine as I assume mine are about as flat as the himalayas. Probably just gonna pull the engine from the car considering how much I'm going to be doing to it.

My biggest concern is having this happen again - so far as I can tell, the cooling system pressurizes fine. Water pump seems to work, and I believe the t-stat may have been taken out by a previous owner, as we found one in the engine bay just chillin. My worry is it may be a sensor/electrical issue of some kind, as the car's temperature gauge was on C almost the entire drive, and very quickly crept up to halfway between C&H. The accuracy of the sensor concerns me because at "operating temperature" that thing was hot enough to cook a turkey on.

For reference, the car still drives (not that I've been driving it, god forbid), and throws no codes.

Has anyone here had a similar experience? I'm ust looking to be pointed in the right direction re: repairs so this doesn't sneak up on me again.

 

[Devin]

It'd be on cool because without the tstat the engine will stay won't warm up properly. How did you diagnose the pump?

 

[stoatmax]

It'd be on cool because without the tstat the engine will stay won't warm up properly. How did you diagnose the pump?

Can't say I've 100% ruled it out, but it's not leaking, and doesn't seem to be slipping on the belt. Other than that I'm not entirely sure how to test it, I figured it wasn't crucial to test as I'm replacing it for 60k anyways.

 

[sperold]

There is no rule that says when you overheat an engine, that it is toast.

If it were mine, it would be toast, as I have a history with that.

But, that being said, if it runs well and is not leaking and stays cool relatively, you probably do not have a problem at all.

Put a thermostat in it and see how it goes.

The engine will either run stone cold without a thermostat, or it will overheat immediately. My bet is yours ran stone cold, once you put the cap back on.

When you refilled the rad when the cap blew off, how much coolant did it take, and was it cool when you replaced it?

 

[stoatmax]

There is no rule that says when you overheat an engine, that it is toast.

If it were mine, it would be toast, as I have a history with that.

But, that being said, if it runs well and is not leaking and stays cool relatively, you probably do not have a problem at all.

Put a thermostat in it and see how it goes.

The engine will either run stone cold without a thermostat, or it will overheat immediately. My bet is yours ran stone cold, once you put the cap back on.

When you refilled the rad when the cap blew off, how much coolant did it take, and was it cool when you replaced it?

The tstat is out still. It runs stone cold for a bit, then heats up very quickly. I drove it for about 5 miles yesterday because I need to transport it to my storage yard and was considering limping it there a few miles at a time rather than towing it. It did okay for a bit but began losing power around the 4.5 mile mark. Got home and it was hot but not insanely so.

The first time I overheated it, the oil and coolant had not yet mixed (much). We mainly diagnosed head gasket failure due to compression escaping through the radiator fluid after it had cooled down and we refilled it. There were hints of oil in the coolant, but not vise-versa. After that last drive however the oil is definitely contaminated with coolant.

My current plan is to drop the engine and strip it down for rebuilding. My hope is that the block is okay, but we'll see. My nightmare would be spending all this money and getting the engine dropped only to find out it's beyond repair.

 

[sperold]

If you let it warm up from a cold start with the cap off the radiator, the coolant will look like Coka-Cola, in a few minutes of idling.
The symptoms sound right for combustion gases getting in the cooling system. It runs cold due to no thermostat, but eventually, no cooling system can cool off the coolant that has super-hot gases injected into it.
But do the coke test just the same to reinforce your diagnosis.
And put the thermostat in, just for peace of mind, that you are not missing something.
If the thermostat was out, the previous owner was probably monkeying around trying to solve an overheating problem, so this may not be as much your fault as you think.

The coolant in the oil is a harder thing to find a test for. Make sure the change in colour is not due to deposits being boiled off the surfaces. It only takes a few seconds for the entire crankcase volume to go through the engine, as it is a high volume, low pressure system, so anything recently loosened will come off quickly.
I think if the oil is contaminated with antifreeze, it will go milky, rather than darker. With pure water, it might not change as much, but i think it still gets milkier.

 

[luigisho]

Secondary things to look at would be to also replace radiator cap with a new one and make sure the hoses aren't collapsing and the radiator is flowing properly. If you are feeling uneasy about the gauge you can look into an aux coolant temp gauge to get a numerical temp read while driving. good luck

 

[gamefanatic]

Coolant in oil isn't too hard to detect. While it can be detected by discoloring the oil this does not always happen. It's usually easier to tell with either a test kit or use the sizzle test. Just heat up a patch of oil just beyond the coolant flash-point (should be less than 300°F). It will boil / sizzle off. If there is no water / coolant in the oil it shouldn't react until it gets about 350°F-400°F...