Odd overheating issue

[chewymilk]

Hello all, I have a 98 V6 SOHC XLT 4x4 that just hit 106K and the cooling system has me a little flummoxed. About 5000 miles ago I replaced the water pump, the fan (a few blades were chipped) the heat clutch the thermostat the radiator and the coolant along with the hoses associated with these parts. I also did a through engine flush (just with a garden hose). I did all of this because I had an occasional overheating issue when sitting in traffic with the AC on. The heat clutch for the fan wasted (it barely had any resistance when moved by hand) and all was fine.

But yesterday when picking my kids up at school it started to overheat again. But if I turned the AC off it would cool down to normal again. It was pretty hot (96f with ~70% humidity) and I was sitting idling and creeping along for about 30-40 minutes. I know I was really taxing the cooling system this time, but I can't believe the AC would put that much of a drag on the system.

It never reached beyond the top mark on the temp gauge (yes I know they are just dummy gauges) so I'm assuming it never did any damage to a gasket or anything. But as soon as we started going to cooled right down and stayed there for a 400 mile round trip drive involving highways, surface streets and more bumper to bumper traffic.

Coolant level and mixture is perfect. Thermostat appears to be working properly. Did two coolant burps to check (again) for maybe trapped air, but nothing. No leaks or anything.

Anyone experience this or have any ideas?

 

[dvdswan]

I would look for a blockage between the radiator and condenser. Possibly bent fins on the condenser.

Since you were sitting or slow moving for 30-40 minutes, that tells you the air flow through the radiator is lacking. New radiator, fan clutch, fan, water pump, etc. It is possible one is bad, just not likely.

When you had the radiator out, did the back of the condenser look clean? Leaves can get in between the 2.