First I thought it was related to my A/C, possibly too much heat from A/C condensor. But it is still overheating with A/C disconnected.

I have no problems driving around town,but once I am driving at hwy speeds for a while in 90+ temp, the engine temp gets too hot.

My fan shroud extension is broken, possibly due to a bad motor mount and I do not have a front lower spoiler on the car. Could these 2 issues cause the overheating at hwy speeds? I do have filler pieces across top and along sides of the radiator.

PS: radiator is just a few yrs old, water flows through core (so water pump is ok) and thermostat was replaced last year. The antifreeze level is ok wth no loss of fluid.

Thanks for any help.

 

what temperature thermostat and how hot exactly is the gauge reading? do you have seals between the radiator and what ever pieces of the shroud still exist? Is this a new problem or did it start after the shroud being damaged?

 

The broken shroud and the missing front spoiler definately not help at all. Are you sure that there is no debri between the condenser and the radiator? This what I found when I replaced mine a couple of years ago.

 

When I bought my 79 a few years ago, it did not have a spoiler on it and my temps were always over 220 when cruising down the highway. Put a spoiler on and the temps now stay below 200 all the time. Mine had a shroud on it so I am not sure how much that will hurt.

 

I too had a bad motor mount. The motor twisted up during a hard launch (like the adolescent that I am) and the fan chewed right through the shroud extension. The fix included changing over to the "locking" type motor mounts on both sides. Talk to the smart counter guy at your auto parts store. I believe they were origionally used on Camaros.
My '74 L48 has been running a bit hot on the highway as well. I discovered that the the shroud seal on top of the radiator, between the radiator and the support, is apparently missing. I ordered a set from Zip and hopefully, that will take care of it.
Truth is, these old cars that we love have always had a bit of difficulty staying cool. To be blunt, they are 7 lbs of @#$% in a 5 lb bag. I believe the big block cars have even more trouble.

 

Answers to the questions in the replys to my overheating question:

I can't recall for sure if the new thermostat is 180 or 195. I replaced it last summer.

On the hwy, the temp started to approach the red mark at hwy speed in 90+ temps, so I pulled over & let it cool down. It was ok after I started it and drove at regular non-hwy speeds.

No, there is no debris in the radiator fins.

Yes, the rubber strips are in place between top of radiator and core support and between sides of radiator & core sopprt.

The top of the fan shroud extension is busted apart pretty bad and, as I mentioned, the front spoiler is missing. Would these 2 issues by themselves cause it to oveheat like this?

 

The shroud and spoiler were put there for a reason, will it help your temps? IMO it definately won't hurt and will be money well spent. Ed

 

When I was a teenager, I had a job roofing one summer, and as I was learning the fine art of nailing down shingles, the guys would always say: "Ya gotta think like water!" meaning, of course, that water finds it's own level, and in order to keep water out, you need to be aware of this fact. In your case, you need to "think like air". Look under your hood, and under the front of the car, and in thru the grill openings, and "think like air". Don't give the air anyplace to go but thru the radiator. Another instance of "thinking like air" is the fact that the spoiler keeps air from going under the car, not only forcing it up into the radiator, but also creating a slight vacuum in the engine compartment, which helps to "suck" the air thru the radiator.

In order for any cooling system to work well, two things are necessary.

1.) The coolant has to flow thru the engine well enough to pickup the heat and bring it to the radiator.

2.) The air has to flow thru the radiator well enough to remove that heat.

Just a few things to keep in mind when dealing with cooling systems. See ya,


Scott

 

Is it higher speed traveling that over heats it, or just higher RPM driving?


In other words, when doing highway speeds, is the engine revving higher for longer periods? If you drove on some back roads, and got on it in 1st through 3rd, higher revs, does that cause overheating as well?

The answer to this questions decides if it's an airflow problem, or a cooling system problem.

 

Running hot on the freeway generally means bad/inefficient radiator, because you should have sufficient air flow. This assumes other components are in good shape. I use the biggest radiator I can; nowadays those aluminum radiators (with their large tubes) are a good option. And I like those Flow-Kooler pumps...

 

The missing chin spoiler by itself will cause this problem.

 

How would a bad fan clutch affect this, and how do you know if it is bad?

 

A slipping fan clutch would probably make more trouble at low speeds. If the fan clutch engages like it's supposed to, when the engine is hot, and you are listening carefully, you may be able to notice the extra fan noise. Also, if you shut down the hot engine with the fan clutch engaged, it will be more difficult to turn by hand.

 

The fan does not spin at a constant RPM, but instead, is controlled by the fan clutch. If the clutch is bad, then the fan is not going to work the way it should. The Chin/lower spoiler in the front being busted or removed will also prevent sufficient airflow from reaching the radiator.

If it idles fine, it's not the waterpump. So the coolant is reaching where it needs to. Question is, is that coolant cool?


Start with the fan clutch. Run the motor on a good hot day, pop the hood, and listen for the fan clutch to engage as the engine heats up. Maybe even raise the RPMs a bit to make sure. That's a 2 hour, 40 dollar fix. If that's not it, then you might want to look into that lower spoiler. Not sure how much they cost, but they are pretty easier to put on, even if you have to make new holes for them. If THAT'S not it, then it's the radiator...and they ain't cheap. Easy way to check the rad is to open it up when it's cool, maybe even drain a bit of coolant out so you can see inside, and look for corrosion, dirt, etc. You aught to see nice shiny copper inside their, for a good rad.

 

 

Thank you everyone for all of your replies. I appreciate your advice.

I generally don't take many lenghty trips on the highway so I don't recall if the overheating started after I failed to replace the front spoiler after being repainted in 1996. The temp only seems to get too high after driving on as hot day at highway speeds for maybe 20 min or more.

I will start by replacing my missing front spoiler.

Then I will replace my motor mounts to replace my fan shroud extension so that way I don't break the new extension due to worn motor mounts.

I hope it is that easy of a fix.

 

Just to pile on, it's hard to overestimate the importance of that air dam. It really does TWO things...first, it diverts air up into the radiator/condenser cavity which (Assuming that all the sponge seals around your radiator and core support are intact and functional) forces said air to go THROUGH rather than AROUND your radiator. Second, it creates a low-pressure area behind it which further tends to draw air THROUGH the radiator. Without it, the opposite occurrs- air flows right past and underneath the radiator, filling up the void in the engine compartment and creating an area of relatively high pressure right behind the radiator and inhibiting airflow THROUGH it. Since your radiator (and everybody else's, for that matter) is a heat exchanger, it can't exchange heat unless a steady flow of air is passing through it. And since a C3 Corvette has less frontal area than almost any 60's American car GM had to come up with a rather creative way of cooling such a big motor with such a small nose. That way was to mount the radiator in what was essentially a sealed box and put a system of vents and dams in front of it and behind it (those vents behind the wheels aren't just there for looks either- try covering them with tape and see how hot it gets) to make it work. As long as all the components in the system are intact and functional, it generally works surprisingly well.

 

I've heard of Camaros and other "bottom feeders" overheating after removing the front spoiler and I can certainly understand why.

If it was just the fan it would overheat sitting still, but not when moving at highway speed.
Just my two cents, I'm no expert. Good luck.