A friend in Costa Rica has a truck with a problem.

How to tell if a motor needs a head gasket or the block is cracked?The radiator went dry so it broke down and I had a mechanic have the head shaved and re-worked and within 100 miles the exhaust is blowing out water again- what did the mechanic do wrong? how to tell if the block is cracked?

I told him.

Since it went about 100 miles before the water returned i would think the mechanic didn't get the head gasket properly installed. Didn't bolt the head down properly,used the wrong gasket, didn't prepare the block properly for the head installation..Or the head needed to be retorqued after a few miles and wasn't. Or the the head was shaved so much that the compression was increased to much and caused the gasket to fail.
Does the oil look a milky brown? Are you sure it wasn't low on fluid when you got it back and caused failure that way?

I also said:
I had a though this morning. You need to check out your radiator. Is it the original one? You could have a very small pressure leak that is draining the radiator. The leak can be so small you will never notice it unless you have a very sharp eye at the right time.

Am i giving him the right advice? I only have experience with blocks cracking due to freezing. Will a block crack due to heat?

Am i telling him the right stuff?

Thanks for looking.

I'm guessing on bad mechanic work. If it were cracked, it would have returned immediately.