Why does my 5.0 love to run at 210F??

[Evil Joe]

This is an overheating problem I've had for some time. My car just LOVES to run at 205-210 F. So far, I've done the following:

1.) New (very large) 2-core radiator
2.) New 16 psi radiator cap
3.) New Stewart high-flow water pump
4.) New high-flow 180 degree thermostat
5.) New water temperature sending unit
6.) Timing set at 10-11 degrees (new timing chain, too)
7.) Flushed system many times
8.) Coolant: 80% water / 20% prestone
9.) "Burped" system by running car with front end 10" off ground
10.) Bypassed heater core (due to omnipresent leak)

In addition, I don't see any bubbles in the radiator fluid when I rev the engine up with the radiator cap off. I've also checked the compression on the cylinders and they are all good. So, I don't think its a head gasket problem.

I think the only thing left is the guage. But, using a multimeter, I checked the resistance from the temp sending unit as a function of engine temperature and it seems to correlate with the guage. So, I kinda don't think the guage is the problem.

I've noticed that after making all these changes, it pauses around 180F for maybe 10 minutes, then starts to climb to 205-210F and stays there.


I am completely out of ideas. Can someone please, PLEASE help me?


It's an 89 5.0 AOD with 135k miles, all stock except for off-road H-pipe (smog equip still intact), 3.55 gears, and air silencer removed.