This truck overheats when the AC is being used, but otherwise runs just about normal. There is no discernable leakage, thermostat is new, the serpentine belt is in good condition. Any ideas?
Please give more details about “overheats.” Does it boil over or does the temp gauge just go up? Not enough info.
Electric fan or engine-mounted?
The 1993 Ranger with a 3L V6 has an engine-mounted fan.
mcparadise is correct, more details are required to answer your question.
If the gauge is erratic, you may just need a new sending unit, which is just about the easiest and cheapest thing to replace on this engine – it’s right in front on top, and costs ~$4.
If it’s actually boiling over, consider having the radiator rodded out. That, or a new radiator, might fix the problem.
The problem is probably because of a partially restricted radiator.
When the AC is off, there’s enough cool air passing thru the partially restricted radiator to prevent the engine from overheating. But when the AC is on, the heat that is emited from the condensor which sits in front of the partially restricted radiator reduces the radiators ability to transfer heat from the coolant into the air. And the engine starts to overheat.