Truck Repair: cummins n14 air presure in radiator, cummins n14, pipe nipples

Question
 I have a '99 cummins n14. Have air pressure build up radiator. Engine runs good, does not over heat. Losing antifreeze out of overflow tank cap due to pressure.

Answer
There are 2 possible areas that cause that problem: 1 is the air compressor.To check if it is the air comp hook a pressure tester on the overflow tank & pump it to around 10 PSI.Hook shop air to the discharge port on the air comp & see if the pressure rises on the tester gauge.If it does the head gasket or head is bad on the air comp.
2 is head gaskets blown.This one is time consuming & needs alot of test equipment that is home made.You need 3 3/8" pipe reducers to 1/4",3 3/8" pipe nipples about 2-3 in long,& 6 ft of 3/8" clear hose.Basically you will take a plug or fitting out of the frt of each rocker housing & install the test stuff.Get a stick or something to hold the clear line up.Loosen & remove water pump belt where it will not turn water pump.Fill with water or coolant & crank engine & see if any bubbles come out of one of the clear hoses.But you most likely do not want to do this test.