Hello,
I have a 1996 gmc jimmy with a 4.3.
problem:I was changing the oil and wile that was draining,decided to top off the coolant.
when I poured the coolant in the radiator it came out of the oil drain hole!The oil was milky as you already have guessed.
Do I have a cracked block or?

thanks in advanced.

 

Most likely cause is a failed intake manifold gasket, but if you just noticed it when you serviced the cooling system, you may have damaged a LOT more.

 

If the oil looks like a frothy milkshake, it's time for a teardown.

 

Blown Head Gasket?

 

That condition cost me an engine replacement not too long ago. DO NOT RUN IT LIKE THAT. pull the intake and go from there.

 

Did your truck ever overheat? Is your radiator in decent shape? Runs fine otherwise? Dont spend your income tax refund just yet...