Truck Repair: 1998 t444e, losing coolant, coolant filter

Question
I recently purchased a refurbished bus for the youth ministry. It has a 1998 t444e (210hp) 2 different mechanics looked at it to no avail as to why it overheats under load. The temp alarm went off and I kept driving a few miles and a hose broke. I had the hose replaced with a new thermostat. I have replaced all the coolant with a new coolant filter. It still ovheats but only when it is full of kids. It can idle in hot weather for 2 hours with no overheatng. I may be losing coolant. (should I suspect a leaking head gasket?) Any help is most appreciated.

Answer
There are a couple things that could cause the overheating......Dirty radiator (blow out with high pressure air, then wash out with a garden hose and sprayer)...The fan clutch could be going bad (if it is not a air clutch fan)...Water pump.....or a possible head gasket prob.  When you check the oil, is there ever a GREY slime on the stick or is the oil a grey milkey color?...this is a sign of coolant in the oil.  The 444E engines do not have a prob with head gaskets much.

I hope this helps, If you are near the St. Louis area I would be glad to help you.