My towing and hauling truck is a '93 Silverado 4x4 with a 350 and auto trans. I've been having cooling system problems:
Started out with the gauge not working = replaced sending unit and wire pigtail
Gauge read really low all the time = replaced instrument cluster.
Gauge took forever to warm up = replaced thermostat that was stuck open.
Now if I drive down the highway it'll run 210-215 empty or 220-225 pulling a vehicle (on a 100 degree day). If I let it sit and idle it'll overheat pretty quick. I checked the radiator and it had a lot of gunk in it so I replaced it with a newer one off of my parts truck which was nice and clean inside but no change. A guy at work told me he'd seen some with the water pump impeller on backwards (pump from a V belt application) so I pulled the pump tonight. But...I don't know if the impeller is on backwards or not...never really paid much attention to one before. Is this right?
Any other ideas? I'll probably do a test for combustion gas in the coolant when I put it back together. But I'd think a head or gasket problem would make it overheat more on the road at speed than it does?
Derek