My 1977 Still Runs Hot !!!!!

[Silverandblack]

Greetings to all,

I have a remanufactured engine with 1200 miles on it, after replacing the air dams, radiator seals. The engine still runs hot, the radiator itself is in good shape, and the front spoiler is new. Also I have tried changing the thermastat to a 160 degree unit, no improvement.
Prior to the new engine the freeway temperature would be 180 degrees, today it ran at 220 on a warm day in California. If I'm caught in traffic 250 degrees appears very quickly.
Would a synthetic oil lower the operating range ?

Any other suggestions would be appreciated

 

[silver 80]

is this a higher horse engine?
might have to upgrade to a better rad.
is it just on the freeway?
I have heard that if the lights are up that we will get better cooling.
just a thought.
tom

 

[silver 80]

I forgot you could also try water wetter or something like that.

 

[Silverandblack]

P.S

Also the fan clutch, and the 7 blade fan are both new, the mix in the radiator is 50/50 .

Idle temperature runs around 200 degrees, but runs up to 250 very quickly

 

[Silverandblack]

One Addition

I did have a RV cam placed in the remanufactured engine.

 

[clar2001]

might depend on the cam if you are runing to slow of a rpm on a built motor it will over heat .
rv cam should be pretty mild does it buck at idle .?

Hi flow water pump............

 

[MaineShark]

First step: switch back to a 180-degree thermostat. 160 is too cold, and can damage your engine.

Second step: since it's running at a fairly normal temp at idle, and too hot on the highway, it seems like an airflow problem.

You replaced the air dam under the nose, correct?

If that wasn't the air dam you were referring to in your post, then check that out, first.

If it's okay, then take a look at your fan shroud. I'm not sure about the changes, year-to-year, but my '79 had a door in the bottom of the shroud that could open or close depending on airflow. If your '77 has the same thing, and that door is missing or damaged, it could mean that your fan is sucking air from under the car, instead of through the radiator.

Joe

 

[78SilvAnniv]

I've had your problem.

I fixed mine with a flex fan.

It has been mentioned that changing the clutch fan/cooling system may not be the fix for everybody...but it was the only thing that CURED my summer run-hot temps.

78 would be okay during the winter at any speeds but in the summer I had to stay under 55 or the temp would climb. AC?...it would shoot up to 240!
We replaced:
radiator
fan shroud
clutch fans (YEARLY!)
thermostats
belts
hoses
engine (GM crate engine, 250hp)

Nothing stopped my run-hot problems until I installed a quality flex fan three summers ago. Now I can drive any speed, any time of the year and with the AC...and the temp has yet to climb over 195. My husband and I have taken the 78 on several "hard runs" in the North GA mountains and she ran just fine, kept up with the big boys.
We weren't puttering along! Much of the driving was in second gear (auto tranny) at 2400-3800rpms.

Search using "flex fan" as the key words and other informative threads will come up for you to read over.
Heidi :W

 

[JBWeaver]

Go with a aluminum radiator. My '77 355ci L82 never gets above 175 here in So Cal. The only problem is the carb kick down takes longer to go to low idle. Even the interior seems to stay cooler.

 

[78SilvAnniv]

A question, JB...

Do you need to do anything special to maintain the life and proper operation of your aluminum radiator that is different from 'regular' radiators?
Heidi

 

[Privategod]

Would a synthetic oil lower the operating range ?

Yes synthetic oil will help it run cooler, but as to how much, I cannot say.
You said the radiator is in good shape, have you had it flushed?
Also, something as simple as a radiator cap going bad can cause cause you to run hot. What mixture ratio are you running as far as water/antifreeze. Even though your engine may not see freezing temperatures, if you are running less than 50/50 you may want to try increasing to 50/50, antifreeze can also help lower temps as well as prevent freeze-up.
What condition are the radiator hoses in, after time, radiator hoses can begin to collapse(?) when the engine warms up, which in turn restricts coolant flow and raises temps. This is more common on the lower hose, which is why most lower hoses are manufactured with a spring inside.
Just some ideas besides those already mentioned above.

 

[Bob Chadwick]

On my 77 the radiator was not completely full for a while. I was watching the overflow tank and the piece of hose that attaches to the cap had come loose. So the radiator was blwoing out to relieve pressure when it was hot but was not able to get the coolant back into the radiator as it cooled.

The cap is a good observation as well. If it doesn't hold the pressure it is supposed to it can cause the car to run hot.

 

[Silverandblack]

The Reponses So Far

Thank you to everyone that responded so far, the hoses on my 1977 are all new, no leaks in the cooling system , the front spoiler is also new. the mix in the radiator is 50/50.

With reference to the idle temperature, left to idle for 10 minutes the temperature runs at around 250 degrees, freeway temperature 220 so it is cooler when on the move. The radiator was recored a few months prior to the remanufactured engine, the air flow is not restricted by leaves etc.

I will replace the thermastat back to a 180 degree unit, thank you for that tip. I also replaced the temperature guage, the temp sending unit is new also.

So I'm not sure what else I can do apart from replacing the radiator , finally the current unit is HD and has the fan shroud in place.

 

[Silverandblack]

ps

The radiator cap is also new

 

[clar2001]

You might want to pressure test your cooling system the pressure gauge goes on were the cap is , if your not holding pressure even a small leak you will boil every time .
I had a olds that had a very small leak on the intake manifold the fluid only dripped out but the system would not hold pressure so it would allways boil over once the gasket was replaced the problem went away.............................

 

[redvett]

If your engine is overbored and bigger cam you are running lean. Headers, exhaust system, intake manifold all change A/F ratio. You should go to someone that has a 4 gas analyzer and have your idle and part throttle A/F checked and have it richened up.

 

[bossvette]

something you may have missed is air in the system the corvette radiator cap is not at the highest point in the system and you may have to bleed the air off also You may want to feel the radiator to see if it has any cool spots which would indicate clogs and as stated before a lean condition can cause it to run hot also advanced timimg can cause hot running

 

[JBWeaver]

Re: A question, JB...

Do you need to do anything special to maintain the life and proper operation of your aluminum radiator that is different from 'regular' radiators?
Heidi

I use the orange antifreeze, recomended by the manufacturer. One thing, I don't use the AC, or can't for that matter. It needs a rebuild. I also don't have the spoiler installed, but it still runs cool.

 

[Jack]

It seems most things have been addressed here ... but the radiator may have residue buildup inside that is not cleaned with readily-available liquid rad flushes. The buildup seriously impedes rad's ability to transfer heat from coolant to the metal core-fins.

Go to your GM dealer ... ask for one canister of GM P/N 12346500 ... it is a strong, dry-powder acidic "cleaner" with a separate compartment containing a neutralizer ... it is Prestone Heavy Duty Cooling System Cleaner (prestone P/N AS100). Canister looks much like a pringles can. Although it's been around for decades, GM recommends it in currect service bulletins for late-models. GM price about $6/can. While there ask them to printout a flush procedure for a late-model. Use it as a guideline. Follow the directions on the can. AFTER you've cleaned the rad ... replace your cap & t'stat. Spend under $20 & a few hours ... Done correctly, you'll probably be pleased.

I do not run DEX-COOL nor any other extended-use coolant ... even in my newer ones/ those with aluminum rads. It's too reactive w/ any air that's trapped ... forms residue too quickly. The green stuff is excellent if you change it every two years ... yes for aluminum too ... and it is not nearly so air-reactive; thus clog-inducing. In a perfect world, cars don't have air in the system ... but like most things, cooling systems aren't 100% ... not completely sealed as the designers had planned. I've posted several times regarding Prestone AS100 and DEX-COOL ... a search will provide more detail.

Synthetic oil may be a good choice ... but dino oil is not the source of this kind of overheating problem. I don't recommend synthetic for older/higher-mileage vehicles whose oil-history is dino ... synthetic often induces leaks in their old seals/gaskets.
JACK:gap

 

[iron cross]

I love to read the overheating problems, some of the bench racing answers can really get wild.:argue