Suddenly, after driving throw 16" of standing flood water left by Issac, my 89 wants to overheat. Warms up normally, temp needle will stay dead center when cruising, but sit idling, and the needle moves quickly to the danger zone. Will spit up in overflow and sometimes hard to restart after shutting down say at the gas station. NEVER had these issues until the water. The upper hose will stay cold, until the stat opens up. Hosed out the rad incase I pick up debris. Checked oil in case water got in the pan some how, but its fine. The coolant level in the rad is always at the neck area touching the cap. Even after I siphoned it down 1", still back to max full after running.

 

If it has the fan clutch then I would think it would be the problem. If it got super wet then there is a chance it caused the temperature sensing spring to mess up and that's why it cools fine driving but when left idle the clutch doesn't engage and allow the fan to turn fast enough when the rpms are low.

 

Yes, it actually got soaked, and in fact, its the original clutch, as far as I know.