Disappearing engine coolant

[TommyT]

My '04 Silverado and my brother-in-law's '00 Suburban both have 5.3s and both have magical disappearing engine coolant. No coolant leaks in hoses, radiators, coolant tanks, or water pump. Has anyone heard of or seen this problem before. Are there any known coolant passage flaws cast in these cylinder heads. any help or info will be greatly appreciated.

Tommy T.

[sprayedenali]

hows the oil look?

[TommyT]

I just changed the oil and it showed no signs of coolant contamination. However there was sludge in the oil filter probably due to the three times it got hot. I checked the plugs also and they looked normal.

[WARLOCK]

I have worked on a few 5.3s that the wter pump gasket was seeping and it would not make it to the floor to show signs of leaking.

[02 avalanche]

I ended up buying a pressure tester from Napa for my 02 avalanche. The coolant loss was driving me crazy, nothing would show up while idling or parked overnight. It ended up being the back of the water pump, where the impeller fits flush against the housing. It only did it under load while you driving. After buying the adapter and presurzing the system it leaked like a sieve.

[TommyT]

I guess the water pump only leaks when its hot and or under high rpm conditions?

[WARLOCK]

They were leaking and the fluid would dissapate before it made it to the ground. Just look for spots where coolant has been running down.

[TommyT]

New pump or can it be resealed?

[02 avalanche]

New pump

[TommyT]

Thanks, I'll double check with an overnight pressure test and go from there.