Overheated, losing coolant

chris78 · Feb 22, 2019

It is an auto, but I have a new rad in it, just installed. After changing engine oil yesterday, I ended up with about 5.5qts in. Today, I drove it around about 20miles to warm it up and check tranny fluid, it looks fine. Engine oil looks high again unless my eyes are bad. I wiped out the filler tube before. Here is what it looks like after the ride.

It smokes, only it quit a handful of times. I did want to do an engine swap, but not this soon. Was hoping it could hold off until I get my garage done.. working in the mud sucks. If the heads are cracked maybe I could find some cheap used ones, or put some new ones on.

My valve covers are turned down, so i'm guessing I would need a set from a later model if I put the newer style heads on? will heads from a 1990 work on mine? Like these?
They only come with guides and seats..
ITM from rockauto

These from ebay are complete for an 86-92, they look like they have the bigger rocker arm surfaces.
ebay

Ianjay · Feb 22, 2019

Intake manifold

I know everyone wants you to replace the heads, but I had a situation like yours and it was not the heads (thankfully), but the intake manifold gasket (which was mentioned earlier in the thread). It has been three years, and the truck (a 1990 2.9 5 spd) is still running fine.
My truck was sucking antifreeze, burning it out the tailpipe and making the oil very brown, just like your pictures. I really thought I was going to need new heads. The truck now has 435,000 kms.
Good luck.

chris78 · Feb 22, 2019

Ianjay said:
I know everyone wants you to replace the heads, but I had a situation like yours and it was not the heads (thankfully), but the intake manifold gasket (which was mentioned earlier in the thread). It has been three years, and the truck (a 1990 2.9 5 spd) is still running fine.
My truck was sucking antifreeze, burning it out the tailpipe and making the oil very brown, just like your pictures. I really thought I was going to need new heads. The truck now has 435,000 kms.
Good luck.

Yea, hehe, well i'm not looking forward to doing that, but I do think I'm going to have to pull the heads in order to figure it out, I plan on getting a gasket set and pulling them. I'm thinking its either a blown gasket, or its cracked. Hoping for the gasket

alwaysFlOoReD · Feb 22, 2019

Like Ianjay says, keep a real close eye on the intake gasket when you tear down. It may be the problem, not the heads, and then you won't have to r+r the heads...

chris78 · Feb 22, 2019

Thanks for reiterating that, I did glaze over it and just saw the word gasket. I assumed head gasket.. I'm trying to wrap my head around how that goes together and where the coolant flows through there. Never tore one of these engines down.

adsm08 · Feb 22, 2019

chris78 said:
Thanks for reiterating that, I did glaze over it and just saw the word gasket. I assumed head gasket.. I'm trying to wrap my head around how that goes together and where the coolant flows through there. Never tore one of these engines down.

There is a cross-over passage at the front of the intake where the thermostat sits. There are coolant passages through the heads are symmetrical, so the ports are there front and back at the head, but dead-head against the intake at the rear.

The lower intake gasket seals these passages where the intake meets the head. The gasket can fail there and allow coolant into the oil. The Chevy 4.3L is famous for the intake gasket failing here.

chris78 · Feb 26, 2019

I got the mainifold and valve covers off. It was full of gunk. The manifold had liquid residue all over from where it was sucking it through the valve cover. I guess thats why it felt like it was running on 4 cylinders at times, but still had good compression, and passed the glove test. Tomorrow I'll take the lower manifold off, hopefully i'll find a busted gasket.

And, while i'm in there is there anything I should do? I was thinking about fixing that stuck/ticking lifter, can I get to that with out taking the heads off?

chris78 · Feb 27, 2019

Thanks adsm. I got the lower intake off. On top of the gasket was more oil/coolant gunk. Underneath was pretty clean. Towards the back of the engine had a small chunk missing out of the gasket, that might cause an oil leak. Above piston number 4, the gasket had a hole between the intake and coolant pathway. Not sure if it was leaking there. Doesn't look like it could go anywhere but down through the intake on piston 4. I didn't see anything else real obvious. If I understand right, if it was leaking where I have it circled, it would still have good compression and only pull coolant in during the same stroke it pulls air/fuel through intake?

I already have an intake gasket set on hand, so either I put it all back together and see what happens, or I pull the heads off and check them.

Overheated, losing coolant

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