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Unexplained coolant loss- Not Cylinder Heads!


falcom

Question

2001 GMC Yukon 4.8

280,000 miles- one owner.

Coolant in oil and loosing about 1 quart in 300 miles.

 

I replaced the heads (they were not Castech) and found tons of gooey coolant oil mix in the valve lifter area. I am at a loss. It seems that it must be leaking in the low pressure side of the of the oil since the oil is 40 psi and the coolant 15 psi.Heads are new. No leakage at head gasket.

 

Is there a knockout plug somehere that coould be rusted and leaking?

 

Is the block cracked?

How do i find out?

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If there is coolant in the oil, Its not the water pump or gasket. Have to be something internal. Also possibility of oil cooler leaking internally in radiator, but when that happens USUALLY you end up with oil in the coolant. Need to pressure test the cooling system and find out where it is going. The Intake is a dry setup( no coolant flows through it) The only thing I can think of would be the block. Or a head or headgasket problem.

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The heads have about 400 miles on them. When I replaced the heads the valve overs looked like they had a jar of lanolin hand cleaner in each of them.

I dont understad how the PCV system would leak that much coolant into the oil.

The Yukon runs good. There are no codes or pending codes. Compression is good. There is no oil in the coolant. There is no coolant smell.

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There are not many ways for the coolant to disappear. It either leaks into the crankcase via a crack in the block, or the head gasket is leaking, or via a crack or porous heads. You may want to look at the timing cover if it has any water jackets or passages for bad gasket, crack or porous. PCV cannot cause coolant to leak into the crankcase.

If this was happening before changing heads, I would rule out the head. But you can't rule out head gasket. Did you check deck for trueness when the heads were off? Cylinder liners also have coolant around them, the leak could be there. You may want to remove the oil pan, then pressure test the system and see if you get any drops from the now open crankcase. This may not show anything. The leak may only happen at a certain temp, and not leak at all at other temps.

Core plugs are on the outside of the engine, if they leak, they do not leak into the engine.

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The heads have about 400 miles on them. When I replaced the heads the valve overs looked like they had a jar of lanolin hand cleaner in each of them.

I dont understad how the PCV system would leak that much coolant into the oil.

The Yukon runs good. There are no codes or pending codes. Compression is good. There is no oil in the coolant. There is no coolant smell.

 

 

See edit in post #2

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Your right..PCV wouldnt cause coolant loss. I was going on the possability that after the engine work ,some air had remained in the system and after purging, appearing as if the coolant had been lost. A quart wouldnt be unsuall. The only reason i made reference to PVC, is that if crankcase gasses arent being drawn back for combustion,they,lle condense and mimick water(coolant) in the oil.Hope you find the problem.

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Got a Mityvac cooling ystem pressure guage today. Put 16 lbs pressure on coolant resevoir for 30 minutes- no leak down.

Started engine and added 16 lbs pressure. No guage wiggle or pressure added.

With engine running released pressure and let it warm up for 30 minutes. Got up to about 5psi. Added pressure to 16 lbs- shut off engine to cool- no leak down.

 

Found a small coolant leak on the new heads where the metal coolant tube crosses over to the other head under the throttle body.

Hopefully thats all it is.

 

Since rebuild I have added 2.5 gallons of antifreez and 2.5 gallons of water. I dont knoe how much is in the front and rear heater cores. Mitchel on demand says I should have 15.8 quarts total.

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Check water pump and wp gaskets

 

Edit:

 

I read your post two ways.

 

You still have coolant in the oil and you know this for a fact

 

You're losing coolant and you're assuming it's leaking into the oil

 

 

Do you know for a fact there is coolant in the oil after the change? You've had the oil tested?

 

After changing heads you still have goo in valve covers? Did you have the heads checked after removal for cracks?

 

Plenty of people have had external coolant leaks they couldn't easily find and have sworn it's leaking internally, when in fact there was no evidence in the oil.

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