High Temp at Highway Speed

[Ralph E.]

Re: Is High Temp at Highway Speed Normal

Ed, thanks for all your help here. I understand the timing advance stuff. I’m just not sure that if you don’t get the advance the engine will run hotter.
I will recheck the lower radiator hose tomorrow when I check the timing.

[Ed Jennings]

Re: Is High Temp at Highway Speed Normal

Insufficiant advance will make the engine run hotter. This problem is maybe more likely to show up at idle than at hwy speed, but it CAN be a problem at hwy speed as well.
I feel it is very unlikely that your carb is too lean without some secondary symptoms of excess lean condition.

[Ralph E.]

Thanks for all the help

I want to thank everyone who tried to help me on this post. I have check and rechecked, timing, spark advance, upper and lower radiator hose, radiator cap, water pump, belts, coolant level and mixture, and owner’s manual. It seems to me that the radiator is getting old and may need to be replaced. However before I replace it, will the rust removers (phosphor acid based) work? I would like to wait until winter to do a radiator replacement. Like I explained the engine is running hotter, 190-210F range. It is NOT running HOT.

[Wayne K.]

Re: Thanks for all the help

Ralph,

Have you considered the possibility that the thermostat might be bad ?

Wayne

[Ralph E.]

Thermostat Works?

Wayne, since the car does not overheat and the temperature elevates and lowers I believe the thermostat is working. I would think a thermostat either works or it doesn't. Your thoughts?

[Mike Cobine]

High Temp at Highway Speed - Square One

Since bits and pieces came together slowly, I've thought about this. Not better than anyone else, but enough to realize a few things need to be organized and we ought to go to Square One again.

-- Previously, engine ran 180-190 all the time, regardless of speed, RPM, and weather.

-- Replaced intake, carb, and distributor and now it runs 180-190 at idle to low speed, then speeds over 2500 RPM it climbs to 200, slowing down then lets the engine heat soak and climb to 210, until it cools about 20 minutes later to around 180-190.

What were the carb, intake, and distributor you had on before?

What are the carb, intake, and distributor you have on now?

Did you have a 50/50 mix before?

Are your belts new and snug?

Did you change the water pump or its configuration (bypass hose)?

Any other changes not mentioned (different exhaust, new mufflers, new tires, mounted the front plate for a change, different oil, engine rebuilt, etc.)?

It sounds like right now that you are at the limits of the cooling and when you run harder (2500 plus) you are taxing it and then when you slow down (less air flow and water flow in radiator) it heats more until the cooling system catches up. But why you are different is something else that you probably need to find out. so let's try again.

[Wayne K.]

Re: Thermostat Works?

Ralph,

Sometimes a thermostat sticks at a point and may not fully open. At slow speed you may have enough cooling with the system but at continual higher speed the cooling system can't keep up with the thermostat not fully opening. As you slow down heat soak causes the temp to go even higher until it once again stabilizes.

Wayne

[Ralph E.]

Re: High Temp at Highway Speed - Square One

Mike, thanks for your thoughts.
In response to your questions:

What were the carb, intake, and distributor you had on before?

The carb was a Holley but incorrect for the car. The intake manifold was from a chevelle and should have had a Rochester carb on it. The distributor was a dual point from a 62 Corvette.

What are the carb, intake, and distributor you have on now?

The carb is a correct replacement Holley. The intake is the correct intake for a 67-327/300 Corvette. The distributor is a rebuilt single point, correct for the car.

Did you have a 50/50 mix before?

The anti-freeze mix was and is measured to be a 50/50 mix.

Are your belts new and snug?

THE belt is new and snug.

Did you change the water pump or its configuration (bypass hose)?

The water pump is a rebuilt original, rebuilt a few years ago. No bypass on 327/300

Any other changes not mentioned (different exhaust, new mufflers, new tires, mounted the front plate for a change, different oil, engine rebuilt, etc.)?

Since the heating issue began I did an oil and filter change, made little difference. I removed the front plate, but that made little difference as well.

[Ralph E.]

Additional Comment

I should add. I installed a balanced thermostat in lieu of the standard type. This T-Stat was used also used in the old intake manifold with no problems.

[Mike Cobine]

Re: Additional Comment

Thanks, Ralph,

I wanted to eliminate the obvious like replacing aluminum intake with cast iron, fat carb passing enough gas to cool replaced with lean one, water pump efficiency changed, etc.

But it sounds like everyone have hit the items you need:
- timing may be off a bit at top end
- radiator may be showing age or clogging slightly
- carb may be a bit lean

Of course, a friend's '72 350 did the same thing (180-190 at 55-65, 210-215 at 70-75) on the Nashville trip and we just basically ignored it since it was hot on the road except to let the car idle a bit before shutting off.

Good luck

[Ralph E.]

Re: Additional Comment

I spoke with Dewitt’s today. They told me it sounded like the radiator was getting old and wasn't dissipating the heat like it use to. I may try advancing the timing a little more. I already set it 36 degrees. After that I'll adjust the carb a little richer. If neither of these work, I try RMI-25 additive to the radiator. This winter or sooner will be a radiator replacement project.
Can the radiator be removed without removing the hood. I hope so!
By the way... what did your friend do?

[Mike Cobine]

Re: Additional Comment

He checked the coolant level whenever it cooled off. If it was too low, he'd add some water, if it puked it on the ground when we parked. Of course, we had to be sure to keep it about two inches below the cap as that is the normal place on the '72.

You might just try backflushing the radiator. I've seen an amazing amount of junk get in them and it could just be clogging a few tubes. Some will literally pour (roll) out of the top opening when turned upside down.

A local radiator shop may be able to help you out but many used to be death on a Corvette aluminum radiator as they would want to hottank it and the hottank is far to caustic for the aluminum. Since more new cars have aluminum and plastic radiators, they are probably much better equipped to help you now than a few years ago.

At $700 for a new aluminum radiator, I think I'd explorer a few local and cheaper avenues unless you were time restricted for a big trip coming up, like a road trip to the convention or whatever.

It could be any weird thing. My '68 on the way back from Bloomington one year wouldn't go over 50 as the belts would slip too much and the pump wouldn't turn enough to keep the engine cool. Under 50 (2000 rpm), it was fine. Over it would slip and heat up. I tossed them in the trash the next day (no place open on a Sunday night) and the problem was gone. The worse was that nearly every cop in the state was in E. St. Louis for the Street Machine Nationals.

If your belts are hard or you got coolant/grease/paint on the belts or pulleys, you might have slippage and it would be a shame to rush into a $700 radiator when $20 worth of belts or a little sand paper might solve the problem.

[Ralph E.]

Re: Additional Comment

Mike, I took the car for a long ride this evening. Outside temperature is about 66F. The engine temperature during both highway and street driving was nearly the same, about 180F. The cool evening temperatures as compared to this passed weekends 90-95F has proved the radiator is not cooling the way it used to. Probably getting old. I think I will take it out and have it flushed and cleaned. If the problem persist after that, it will be a call to Dewitts.
Thanks again for all your help.