I have a stock 1969 Mercury Marauder X-100 with a 360HP 429CI engine.

If I run 75-85 MPH (A/C off) the engine heats up to about 210 degrees. If I back off to 65 MPH the temp drops to about 200-205.

1st... Is this normal for this engine???

2. If not what is the solution.

Please note. Everything, heat related, appears to be normal and in good condition (air flow, water punp, fan, radiator, block, coolant, etc.) Normal stop and go driving, in Florida 90+ heat, with A/C on, does not cause overheating, if 210 is overheating....

One theory is that at high speed the water flows trough the radiator too fast for it to cool sufficiently, consequently, slowing down allows the radiator to cool the water. If this is true, what is the problem/solution???????

ANY help would be appreciated.