429 Overheating at high speed

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.

50% water to antifreeze? Wrong mixture gives a higher temp. Lower radiator hose collapsing? Check the spring. Do you have a thermostat installed?

if your radiator is old, you might need it rodded out or a new core, and if you're in that process you might as well get the block flushed..... a good addiation after doing that would be to put a coolant filter in your upper radiator hose, you will be amazed how fast it clogs up with small particles of iron and such..... cooling system is always one of my main things i always try to keep in perfect shape, with the hot summers and bad traffic we get here in san diego, you dont want to be caught with an out of par cooling system

I don't necessarily feel that a 10* F rise in temp under the change in circumstances is alarming...might even be normal.

The posts above are all noteworthy. Remember that water cools better than antifreeze does; antifreeze primarily raises the boiling point/lowers the freezing point of your coolant. It's also a waterpump lubricant.

If you reguarly drive this car at the higher speeds, here's some food for thought: The fan shroud is there to enable more efficient cooling at slower engine speeds and slower driving speeds (which is how most cars are driven). Since the shroud embraces the perimeter of the fan blades, cool air is more efficently drawn through the radiator. But at higher speeds the shroud actually blocks the ability of the air to pass through the radiator at the rate it needs to pass with the sustained high engine speed/higher engine work.

Again, I don't think a 10-degree rise is particularly alarming under the circumstances.

Paul

i agree that 210 is not overheating on that motor, it should run safely to 220 maybe a little higher than that.... but the simple cheap maintance is worth not having it become a problem