I need help. I had overheated the motor a while ago, and finally got around to doing the repairs. Pulled the head, had it planed and a valve job. Reinstalled it, new water pump, thermostat, of course all new gaskets. New aftermarket radiator and cap. Electric fan works. Started and ran fine. Still overheats (according to the gage) over about 50 mph, or heavy acceleration. Only thing I didn't do is change the fan clutch, but it doesn't overheat at idle. Gage seems to work, I don't want to peg it, comes down when I slow down and let it idle. Do these things get air-bound ? Could the timing be too advanced? It does not have the original computer, it was cooked by a shorted O2 sensor wire, I got another from a salvage yard, seemed to run all right when I replaced it. Is there an OBD II socket on this year? I can't find one. Seems to have too much power and run too smooth to be running lean. What have I missed ? Anyone have any ideas ? Thanks for any help.
Jim

 

Did I miss a new radiator? Yep, I missed it, my bad. Have u verified temp with a infrared temp gun? I'd recommend a new fan clutch anyway....that's the only major cooling component left to replace.

 

x2 on the fan clutch. What year is it? Since you're going solely off the temperature gauge, you might have a faulty temp sending unit. You could even try replacing that too. Cause based on what you've told us, the coolant isn't actually boiling and overflowing right?