Tractor Repair: coolant blowing out, head gasket, cracked head

Question
I have a John Deere 1520,using it today I noticed coolant coming out the overflow,did not get hot and when i looked in the radiator it seem the pump was working.Though the cap my be bad so I switched the cap off the JD 3020,but still the same thing.What should I check first?

Answer
Hello,

  It's possible that a bad  head gasket or cracked head is leaking and letting compression from the engine into the cooling system, pushing out the coolant.  With the radiator full to the top, run the engine and watch for bubbles in the radiator.  Bubbles constantly coming to the surface means there is a leak.  Some shops have a tester that can check if there is carbon monoxide present in the coolant.  A positive test would verify that engine exhaust is getting into the cooling system from a bad head gasket or cracked head.  A wet sleeve engine with a cracked cylinder sleeve can cause it also.  If the engine is not overheating, then these are the only other things that can push coolant out.