Changed hoses, flushed system with cleaner, removed t'stat, replaced fan clutch and temp sensor.
Question = have a 2002 GMC 1500 5.3 L 2WD extended cab, 183,000 mi. Two weeks ago it ran hot~ 250+ when I got on the interstate. Once I pulled off the temp dropped. I found the suction hose collapsing at ~1500 rpm. I replaced the hoses, flushed the system with cleaner but now it runs at 235 will drop then run up again. I have removed the thermostat, replaced the fan clutch, checked the fan, checked the water pump and pressure washed the exterior of the radiator core. It's not the gauge or the sensor. The temp builds gradually to about 200 then quickly rises. It will drop but eventually stabilizes at around 235+-.
What do you suggest I try next? New radiator. compression check.
It seems that doing a coolant flush helped the problem. This may because it was dirty. I would suggest having the radiator checked for be restricted. If you can get a laser infra red thermometer, let the engine get hot at idle, then test different areas of the radiator looking for cold spots. You would notice a large difference in temperature. This would indicate there is no coolant flowing in that area, so it is restricted.
With the engine hot and running, look for bubbles in the cooling system. This would indicate a blown headgasket.
I would also do a compression check to look for a headgasket problem.
2002 GMC Sierra Running Hot