I have to have my electric fan on all the time, even cruising down the highway. Timing is good, carb is little fuel rich, lower air dam intact, 3 core radiator in good order. I do have a true cowl hood, so would it be possible the effect of the cowl induction is slowing the air through the radiator?

 

Overheating at low speeds/idle is usually due to lack of air flow through the radiator. I doubt your hood is an issue as the air comes in from the front. In my experience, overheating at highway speeds is usually related to a lack of water flow through the cooling system. Double check the radiator and inspect your water pump to ensure it is working well. While running at normal temps, squeeze each radiator hose and see how quickly they pump back up. Should be instantaneous. Take the belt off and make sure it rotates easily, doesn't leak, and the shaft has minimal play. Your impeller could be in bad shape. Submerged in coolant, ferrous metals do erode over time. There is also the possibility your lower radiator hose is collapsing at high speeds. I had a similar issue in a `72 LeMans that was helped by installing a spring into the lower hose. That's something modern cars don't have, as the rubber is supposedly better today. How many miles on the engine? New engines can run hotter as they are breaking in.

 

Thx for the info, the motor has maybe 3k miles. 9.3 max compression. The water has 2k more miles plus its 7 years old. Lower rad hose is ribbed, upper is not ill check ot out.

 

So the coolant is 7 years old?

Even with the low miles, I would thoroughly flush and refill. The old "green" coolant is designed to be replaced more often. Make sure you mix of coolant/water is good. I usually shoot for 50/50. You could add some "water wetter" to the mix, too.

 

No sorry, the water pump is 7 years bout 4k miles. The coolant is maybe 500 miles old is 60/40.

 

Also make sure you never never mix the orange and green coolants, unless you want jello in your cooling system. Seriously, they go through a chemial reaction that makes them into a Jel-like substance. Pretty gross.


Have you burped the radiator? Might seem silly, but I've seen people not do it when flushing the system. the lower hose collapsing is a sneaky one, hard to identify.

Other than that, backtothe80's summed it up pretty well.

 

do you have the air deflector under the front of the car??

 

You may have an air pocket. Burp the system.

 

Yep ive burped an burped. Thanks guys, just wanted opinions that it wasnt the hood, im replacing this motor as soon as i can.