I have a 67 250HP 326 in my 65 Pontiac. Engine is stock except for Edelbrock Performer cam. My heat problem is opposite of most. I can drive around town, or idle ALL DAY and never go over 195 degrees(w/180 thermostat). When I hit the highway it slowly creeps up to 220-230. If I exit and start driving street again or even just pull off and let it idle, temps drop back down to mid 190's within 5 minutes. Never overheats on street, only at highway speed. I observed flow with cap off and it moves well when t-stat opens, no boiling over or spillage. I'm running 50/50 although I'm in So. Cal and don't need any freeze. I have a flex fan and factory shroud in place. I've used Wetter in my other Pontiac but never in this one. Since the problem is specific to highway, I don't think chemicals are the issue, but if I knew the answer I wouldn't be asking you guys. Any help appreciated! Ya'll haven't let me down yet!

Brian
[email protected]

I have a 67 250HP 326 in my 65 Pontiac. Engine is stock except for Edelbrock Performer cam. My heat problem is opposite of most. I can drive around town, or idle ALL DAY and never go over 195 degrees(w/180 thermostat). When I hit the highway it slowly creeps up to 220-230. If I exit and start driving street again or even just pull off and let it idle, temps drop back down to mid 190's within 5 minutes. Never overheats on street, only at highway speed. I observed flow with cap off and it moves well when t-stat opens, no boiling over or spillage. I'm running 50/50 although I'm in So. Cal and don't need any freeze. I have a flex fan and factory shroud in place. I've used Wetter in my other Pontiac but never in this one. Since the problem is specific to highway, I don't think chemicals are the issue, but if I knew the answer I wouldn't be asking you guys. Any help appreciated! Ya'll haven't let me down yet!

Brian
[email protected]

Clogged radiator http://forums.performanceyears.com/g...n_rolleyes.gif

how many dead bugs and leaves are on the front side of the radiator? Many people will flush the whole system and never look at the front of the radiator.

Is the car missing a shroud or air dam?

1981 Trans Am, 462ci/4sp
1995 Formula
1963 Bonnie (for sale)

Having had this same situation my vote is with Kenth.
Whole bottom half of the core was clogged.

Ditto Kenth's answer. http://forums.performanceyears.com/g...n_rolleyes.gif
Do a flow test on radiator if possible.


Another Red Light Nightmare http://forums.performanceyears.com/g...icon_smile.gif

Check your distributor and make sure your mechanical advance is working properly. I had the same problem that you're having with my '68. It turns out the advance mechanism in the distributor was not giving me all the advance the engine required. I disassembled the distributor and cleaned the breaker plate and advance weight holder where the distributor shaft goes thru. I also cleaned the distributor shaft. There was dirt and gum here, which prevented the advance weight holder from moving fully. I then reassembled the distributor. The advance mechanism in the distributor now functions as it should.

Also, you may want to check the vacuum advance unit and make sure that that is working properly as well.

At highway speeds, you should be getting about 45 degrees BTDC total (including vacuum) advance. Your total timing, without vacuum, should be around 34 degrees BTDC. With the problem above, I was getting about 25 degrees total, without vacuum.

You'll need all that advance to get the car to run cooler on the highway. Retarded timing will always cause the car to run hot.

If you feel uncomfortable doing the distributor work, find a shop that can do it for you.

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Curiosity is good!

Nice post Goathead. Lots of good informantion.

you might check the heat riser in the exhaust manifold. make sure it operates smoothly and actually does opens when it should.

i have experienced similar problems and that was the cause.