Tractor Repair: Ford 3910 overheating, ford 3910, radiator shop

Question
I have a 1988 Ford 3910 diesel tractor that has been overheating. I drained and flushed the radiator and block. Still it was over heating. I then replaced the thermostat and it is still running hot. It appear that the antifreeze isn't circulating since the radiator is still cool on the bottom half. I removed the belt and the fan/water pump turns freely (manually). The water pump was replaced two years ago. It isn't leaking nor is the shaft loose. Before I try replacing it, is there something else I should be checking? Is there an air release value that should have been open when I refilled the radiator? Or is there still a possibility of a blockage in the system somewhere? Thanks!

Answer
Hello,

  There are a couple of things that should be verified.  If you think that it is overheating because the gauge says so, and no other reason, the gauge could be inaccurate and possibly it is not really overheating.  The actual engine temperature should be checked with a thermometer or infrared heat gun.  It is normal for the bottom of the radiator to be much cooler than the top, but if it is still real cold while the engine is too hot, then the coolant is not circulating as you said.  Sometimes radiators get restricted inside as they get old, and no amount of flushing will clean them out.  A radiator shop can either clean them with the ultrasonic or chemical method, or by physically taking the radiator apart.  I know a radiator shop that has a flow tester that they can hook up to the radiator and check how many gallons per minute will flow through it, and compare it to the specifications for that particular radiator.  This will tell them what percentage restriction it has.  Some machines are very prone to air lock when the system is refilled with coolant.  I don't know if yours has it, but some engines have a plug on the cylinder head or thermostat housing that can be loosened or removed to bleed the air out.  Sometimes the fins on a radiator will look clean on the front so people think there is no dirt restricting the air flow through it, but if you shine a flashlight on one side and look on the other side, you can't see light coming through between the fins.  They sometimes plug with dust and dirt in the center instead of on the front where it can be seen.  I've had people tell me their engine is overheating because it pushes coolant out the top of the radiator when they run it so they think it is boiling over, but when I check it out, I notice that it does it even when the engine is still cold.  This tells me it is not overheating, but has a blown head gasket or cracked head.  If your engine has a fluid coupling to drive the fan,(some people call it a fan clutch) it could be faulty and not driving the fan at the proper speed.  The only way to accurately check it is with a photo tachometer.  I have also seen thermostats accidentally installed upside down.