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Here are some common signs of a warped/cracked cylinder head:
1. smoking from tailpipe
2. loss of cylinder compression
3. engine misfiring
4. loss of coolant (internal or external leaks)
5. loss of oil (internal or external leaks)
6. coolant mixed with oil (finding coolant on dipstick)
There is no easy way to check the cylinder head if it is on the vehicle. You need to begin by having a block test performed. Most repair facilities can peform the block test and let you know if there is an internal leak between the block and cylinder head.
You will have to have the head removed and pressure tested to make sure it is not warped or cracked. Sometimes the crack can be so small you really cannot see it. Alot of the time, the crack is on the part of the cylinder head that meets with the engine block.