I have a 1979, L-82, M-21, 4-speed with the rare factory rear gear (3.70) in it. The car has 40k actual miles on it.


The water pump went out so while replacing it I also cleaned out the radiator, installed new heater core, new thermostat (160), new hoses and new foam seal around radiator. I know the proper thermostat is 190 but a 160 was in there so I replaced it with a new 160. I did not replace the sending unit because before the water pump went out the temp gauge read 170 - 180. The water pump was a stock replacement. It looks identical to the pump that went bad.


The motor runs cool in the spring and fall. But when the weather gets humid (Iowa) the motor runs hot. At 70 mph the motor is turning 3500 rpm so I don't run it there because the motor is winding to high. At 60 to 65 mph it runs at 210 and slowly creeps up the farther I drive. I have to run it at 55 or less to keep it from creeping up. When I get off the highway and back into town driving, it cools to about 205 - 210 again and stays.


The motor is stock. The air pump and bracket and A.I.R. tubes have been removed. (done by previous owner) The only modification I've done is install a Magna-Flow 2.5 inch duel exhaust and installed a set of 3E spark plugs. I don't think so but could the spark plugs be causing it to run hotter than normal?


The car is an A/C car (that works) but I only run the A/C during warm up to lube the system. Never run it while driving. So it has a factory auxiliary fan on it that kicks on at 225 degrees. I've never noticed it kicking on while driving but after I've parked the car for a while and go to restart it, it will kick on. So I know it's working. My question is, if or can I put on a different electric fan thermo sending unit that will kick on the fan at a lower degree without doing damage to my electric fan, wiring, etc. Summit has some different ones. I want to keep the car stock so I don't want to get rid of factory cooling set up and replace with aftermarket electric fans, different radiator etc.


I should also mention that the system had a 6 blade flex-fan on it and I replaced it with a stock 5 blade with h/d clutch. Everything I've done has lowered the temp in hot weather but I want to get it down closer to normal operating temp. (190) and maintain a constant temp whether out on the highway or in town. Can anyone offer something that I might have overlooked? Spring and fall driving are a pleasure with the temps around 170 - 180. These temp readings are from my factory temp gauge.


Thanks, Bagger

 

Get an infrared thermometer and check the temp of the upper radiator hose to confirm the temp reading. Then check the lower radiator hose to make sure it doesn't collapse under load.

 

Make sure the radiator seals are in place and the chin spoiler is there. The radiator support to the hood is very important.

I changed to a Dewitt's and the temp dropped 15 degrees.

 

Not sure about '79 radiator shrouding, but my '73 ran 15 degrees hotter with the round shroud extension off (383 w/stock radiator, fan, & water pump).

Steve

 

Do all of these. I kept reading to interject but all my suggestions have been said. Follow everyone elses suggestions, they are all on the money.

If you just squeeze the lower radiator hose with the motor off, you should feel the support spring inside or it should be stiff

 

Two questions:

1. Do you have a front spoiler (air dam) under the nose? That is important as it deflects air up and thru the radiator. That is its purpose....not for aerodynamics.

2. Is your timing set properly? If you timing is retarded, or if there is some problem with the mechanical advance in your distributor the engine will run hot. And the faster you go, the hotter it will get. You need to put a timing light on the engine to see if ignition advances properly up thru about 3500 rpm.

 

Original radiator may need to be flushed/cleaned.

 

If you do all the above and still have problems overheating, try taking the intake manifold off and inspect the water-coolant jackets. On my 81 I nearly pulled out my hair chasing this issue, replaced just about everything, even an aftermarket alum radiator with dual electric fans. Still over heated. Then one day I took the manifold off to replace it with an aftermarket piece, there was junk built up over the years in the manifold where the coolant passes through. Put the new manifold on, overheating problems are gone forever. THE END.

 

If I am reading your original post correctly, your overheating issues started with the replacement of the water pump, and the other work you did at the same time. If that's the case then you need to go back and figure out what you changed that is causing the problem. If I have misinterpreted your post, then I would agree that timing is the first place to look.

I have a 427 small block inn my '79 with a completely stock cooling system, and have never had any cooling issues. Admittedly ambient temperatures over 100 degrees are rare around here, but the car runs at 180 degrees all day long.

 

First off I would like to THANK everyone who replied to my thread.
Things I have done:
Bought infrared thermometer last year and ran a temp check. Everything looked ok but will check again this spring.
Replaced all seals with new. That helped a little.
My car was ordered with the Pace Car spoilers. That's what I'm running.
I am running a full stock shroud with stock fan and H/D clutch.
I do have a spring in the lower radiator hose.
I will check timing. Had it tuned up a couple years ago. My mechanics are pretty dependable but something might have changed.
Radiator was flushed when water pump, heater core, and everything else I described in my original post.
Motor has never been apart so the last thing I will attempt is pull the manifold only when all else hasn't worked.
And if worse comes to worse, I'll do like I'm doing now and on those 85+ degree days, I leave it in the garage.
Thanks again Gang!

 

This grabbed my attention. I don't believe a 4-speed with 3:70 rear is a rare combination. 3500 RPM at 70 is normal and as designed. It should run 3500+ RPM all day.

 

You're absolutely right, but you get about nine miles per gallon and you need earplugs.

 

My Corvair (3.55) would run 3500 RPM all day, too, and it didn't even have a radiator. The point is still that GM designed these cars to do exactly that. The stock cooling system should work, if the rest of the parts are in order.

Since it looks like the rest of the parts are working, what might remain are:

Timing! Even if your mechanic did it "correctly", it may not be best practice. By 3000 RPM, you should be all-in with mechanical advance, 34 to 36 degrees. Your vacuum advance should give you another 10-12. This is easy to confirm with a digital timing light. If you haven't already, email Lars on this forum for his timing papers. This will give you the best practice way to set your timing, and to set-up your distributor. If your mechanic set the advance at idle, any number off things could be wrong. Bonus: With correct timing, and a properly set-up distributor, your car will be MORE fun to drive.

Air bubble in the system, or bad water pump? There are a number of messy ways to diagnose this, including running with the radiator cap open. Also, do you have the heater hose bypassed (looped back from the intake to the water pump), or shut off completely? If neither, try running the car with the heater on full next time, if you can stand it.

That's all I got. If none of the above fix it, you may just want to spring for a new radiator, but it sounds like what you have should work.

 

The Corvair was designed to run without a radiator, and had cooling fins on the heads. Not a fair comparison imho. I helped my father rebuild several of these (Corvair) motors while growing up. Our motors will overheat if the cooling system is not right.

 

I fully agree. In your example above, the intake was gunked up. If the the cooling system is not right, these cars (Corvettes) will overheat. My point was that GM designed these cars (Corvettes, certainly, but also most GM cars of the 60s, 70s, and 80s), to drive at highway speed all day, provided the cooling system is working as designed.

 

So, did you just flush the radiator? It may be still partially clogged. Why are you really running a 160* stat, just because someone else put it in there? Your system WILL NOT run cooler with a 160* stat, it's only to control the low side temp. Once the stat opens...Its wide open and if the rest of your system is not up to the task, it will still run/get hot. If you are getting hot while driving down the road, you have flow issue with your antifreeze and since you said you have replaced the pump, hoses, stat, foam seals and heater core, that only leaves the radiator as a major player. If it gets hot at idle, you have an airflow issue. Does the 79 have a clutch fan and if so, have you checked it? I'm assuming it does, since the 90-82 do. If you decide it needs replacing, I would go with a Hayden clutch fan, not some junk made in china stuff.

If everything is looking OK, I would have a harder look at the radiator and also replace the stat with a stock 195* or at least if you like a 185*. With everything working normal, the cooling system will run just fine with a stock motor...it's the way it was designed to run. Post up any new developments.