My 2000 4.7L overheats. I've replaced the pump, thermostat, clutch fan, and coolant (correctly). When flushing the radiator with a garden hose on full, there is plenty of volume coming out but there is some back pressure. If the heater is turned on, the temp will stabilize and even cool the engine. This leads me to suspect the radiator yet like I said it has good flow.
Would the O2 sensor or any other sensor be the cause. Does anyone know of a similar problem or cause? Thanks!

 

Your heads are most likey warped.did it overheat severly several times and get extremely hot.if so,yes they maybe warped.how low was the coolant before repairs?.the only ways to make sur is do a cyl leakage test or take the heads off and chk warpage with a flat edge.

 

if you have access to a cooling system pressure tester than you're set. disconnect the radiator cap, with the engine cool and the system not under pressure, and connect the pressure tester too the radiator filler tube. put the system under 15 psi, do not exceed 21 psi or damage can occur. if the needle stay at 15 psi for around 2 minutes then you're system will most likely check out. if the need drops slowly then you have a small leak. check around the water pump and your hoses. if it drops quickly then you definitely have big issues. before you even go to remove your cylinder heads to check for coolant blow by into the crankcase or the combustion chamber, remove your drain plug and drain your oil out, just a little bit, note what comes out, color, etc. if it comes out green, thats an internal leak since water is heavier than oil. if it's milky, still an internal leak. another way to check the system pressure is to put the pressure gauge on the filler tube and start the engine. if pressure builds immediately, you have either a crack in your block or a head/head gasket problem. should build slowly. if that needle doesnt build up, pump the tester to 21 psi and note if it fluctuates or not, fluctuation indicates cylinder leakage. if it doesnt move then race the engine a few times to see if it abnormally fluctuates and see if you notice an sweet smell or steam coming from the exhaust pipe.

also, are you sure it's overheating and it's not your temp sensor on its way out?

 

The raditor is usualy blocked at the fins where it meets the side tanks, But the damage has already been done.do a co2 test to confirm but the heads are very easily warped.

 

i dont wanna be a dick, BUT THAT SUCKS