I have a 1990 serengeti with the same motor. I beleive your problem is pretty simple. Clean/blow out the lower portion of the radiator. The radiators get plugged up behind the fan shroud thus resrticting air flow for cooling. If this continues to plug it will create excess strain on the cooling fan blades leading to fan explosion which will destroy the radiator. Once this happens and you get that new fan, water pump, radiator, pay the 5g they cool great!

Just saw your reply about the overheating on a 1990 Safari going up hills. We had the problem and the fan did have an explosion. Now we can't find the fan to replace it. Any suggestions as to where this darn fan can be found. We have located the water pump, but can't find the cooling fan. We can find the parts number either. Help! We are full timers and need our home back.