This weekend I took my two favorite ladies out for a drive. My wife and my '75 Coupe. Wifey loved the fact that I purchased a C3 with a/c. She has long hair.....anywhere where was I?

In the heat and humidity of Florida, I have to admit pumping cool air through the cabin area was schweet....

About 50 minutes into our drive I noticed the temperature gauge was approaching the red. I shut down the a/c and the temperature returned to somewhere around 200 degrees.

First of all, what is the correct operating temperature for my '75/350c.i.?

I got it home and starting working on a rear end noise again as well as replacing some 35 year old strut rods. Bottom line: I haven't yet checked for the presence of a thermostat. Could a malfuntioning or non-existent thermostat explain the issue? Funny thing is that I did not once smell coolant.

Thanks, in advance for all of your help.

 

i would check the coolant level first and buy a good ir temp gun to check the gauge calibration next....good luck....

 

My '79 had overheating problems with a flex fan and shroud while the AC was running. All of my temp control devices and gauges were working. I ended up getting rid of the crappy fan/shroud setup and going to electric fans.

I know a lot of other people don't have this problem so I can't really help, I can just sat my stock A/C and cooling system did this when I got my car and the weather was really hot.

If there was no thermostat, it shouldn't run hot it SHOULD run too cold. If it was stuck partially closed it could run hot like that.

 

Yes check the coolant level, and also check the thermostat for correct operation.
Next, get out your vacuum cleaner and do your best to clean everything out from in front of the rad. I put a new rad in my car a few years ago and was suprized with the amount of trash,fluff, and general bad stuff collected in the rad fins in such a short time. The best way to do it is remove the rad, but with a little duct tape and a short piece of copper pipe you can make a tool to stick on the end of your vacuum hose to clean things out.

 

Hi K,
I believe it's also important to check that all the seals on the 4 sides of the radiator, and the one on top of the core support, are in place so the fan pulls the air through the radiator and not around it.
Regards,
Alan

 

Thanks everyone. I am going to go ahead and change the thermostat. It's pretty cheap insurance.

I have a follow up question. I drove the care to a Vette 'guru' (closed for lunch...dang!). Anyway his shop was about a 20 minute drive one way. When I got there I spun the fan and it moved freely....very freely.

Shouldn't the fan clutch be pretty much locked up at that point?

I do have plans on converting to an electric fan(s). Keeping in mind that I'm a newbie, is this something that I can install and wire? Do you have a source for the electric fan conversion?

Thanks...

Kirk

 

Investigating this one thing I found is the lack of a coolant reservoir. The hose from the radiator seems to be there. There is a hose that runs from the radiator along the left fender and just stops. So now I'm in search of reservoir since I'm certain it's rather important. Then, because I have yet to detect the aroma of coolant, I'm going to replace the thermostat and the radiator cap.

One thing I've also noticed is that whether the car is cold, or after a 20 minute ride to the auto part store, the mechanical fan turns exactly the same. It spins completely free.

I've had differing opinions of whether that is an issue or not. For $40, I can replace the fan clutch. Is it worth pursuing?

Thanks...

 

My 79 would run hot after high way speeds, fan would spin freely by hand.
Replaced the clutch and it dropped 20 degrees on the gauge.
Time for a new fan clutch i'd say.....

 

Left fender? I hope you mean right (passenger side) fender. Sounds like somebody tossed the coolant recovery reservoir. If so, then your car is probably running low on coolant. That alone will give the symptoms you've described. The rad should be 100% full at all times.

 

M.W. Quite right. I described the wrong fender. I'm shopping a new reservoir, cap, etc. to replace this part.

Fan clutch is next.

Aluminum 4-row radiator is next if the above doesn't work.

Then a dual-fan configuration to hopefully wrap up this issue.

 

did you forget about replacing the t-stat? thats an easy and cheap thing to eliminate now b4 you go sinking more time/money,then realize it wasnt done earlier......

 

Thanks.....It was on my list but I forgot to mention it in my reply. I have tried to research the correct operating temp of my Vette to make sure I purchase the correct t-stat. I'm having little luck.

On a side note, I have recently been introduced to a "fishbone" method of problem solving. I realize to some this isn't a new technique but as a computer network engineer and a "car guy" anything that will help me speed up the identification of root causes of a particular problem is "all good" to me.

Thanks again....and bye for now...

Kirk

 

One thing people overlook is the chin spoiler. I doubt that is the "problem", but sometimes people take those off without realizing that it is a functional spoiler that helps scoop cooler air off the pavement to push over the radiator.

I think the proper thermostat rating for your car is 195 degrees for reasons that I can't remember at the moment.

 

No idea what fishbone method is, , but I'll tell you what I always do with a new old car. Remember over 65% of engine problems arise from cooling issues, and that is particularily true here in Florida.

It sounds like the car is new to you so anything is possible. Here is a pic of a 75 lower cooling hose and surprisingly, the car did not run hot.



The first thing I do is a serious flush of the cooling system.
Remove the tstat because it restricts flow for flushing, reinstall the housing.
Attach a garden hose directly to heater core fitting on the intake manifold, a lot handier if there is an inline valve close in the hose.
Remove the lower and upper hose at the radiator.
Remove the 2 block cooling plugs (just above the oil pan on each side of the block) (replace with brass /14"npt fittings with hex heads when done).
Flush with the hose multiple times to get all the loose stuff out, you can hold your hand over the lower hose to let the engine fill completely.
Check the lower block holes for the crud coming out.
Now do the same thing with the radiator only.
Now reconnect the heater hose and fill the system with clean water and a good radiator cleaner (I use oxalic acid).
Follow the directions on the bottle.
Let the engine cool and repeat the first flushing steps with the connected hose and block plugs out, but you can leave the radiator connected and drain with the drain plug on the bottom of the radiator tank.
Clean the fins of the radiator with a decent water spray from both sides. It won't hurt to use a good degreaser a couple of times. There can be a lot of junk in there.

Your engine came with a 195° tstat. Get a quality one and install.
Refill with 50/50 antifreeze and distilled water, waiting for all the air to bleed out. The bleed holes in the tstats are very small so it can take a little time. Fill the radiator completely full cold.
Start the engine and when the coolant expands and starts to overflow replace with a new cap.

Now you are ready to drive and to diagnose any real cooling system issues if any. If your coolant tank is missing, you will puke a little coolant until the engine finds it's hot coolant level.
Most important rule is to not add or remove coolant with the engine HOT.
The absence of the overflow tank will not affect your cooling temp at all. It was put there to prevent antifreeze from contaminaing the ground and to prevent the presence of air in the system which promotes internal system corrosion. A gazzilion cars were made without the tanks. You can get a new tank and lid for around 25 bucks from any vender.
I drove my 77 in S Florida for 3 years without the recovery tank and no seals under all conditions with no extra coolant loss and maintained tstat temps, always.
And I also didn't replace the pictured lower hose on the 75, although it is clean after flushing and I do have new ones on hand.

Hope this helps a bit.