Coolant in oil
 

My car just began using antifreeze with no loss in engine performance as you would expect with a head gasket. Coolant rapidly ends up in the oil sump; however, when pressure testing coolant system it holds????? Any ideas?

Finding an antifreeze leak
 

A compression check is your first option here but an intake gasket leak is also a possibility. Do a very careful visual inspection of the intake gasket mounting surfaces (you'll need a droplight to see underneath it) while the engine runs. If absolutely no antifreeze leakage is visible, move on to the compression test to check for a leaking head gasket.

FYI: This will receive more replies if you post it in Tech.

Head gasket?
 

My first thought is a head gasket leak. If coolant is disappearing without any visible puddle under the car and no steam emminating from the engine, well the coolant has to be going somewhere. Look for white smoke out the exhaust. That's really steam from the combustion chamber, and always shows either a head gasket leak or a crack in the head or block.

I am somewhat surprised that the pressure chek on the heads showed no leak down from the coolant passages since that coolant has to be going somewhere. It is making it's way into the oil. It must be being forced past the rings or from a cracked cylinder into the bottom end.

My bet is the head gasket.

Rev

I would bet the head gasket as well, but when you pull the intake off check to see if it looks like the gasket was letting coolant get past it and into the lifter valley. The very front port on both sides are the coolant passages, btw

If those look ok, then just go ahead and change the head gaskets. I'm betting thats what it is