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running hot



i need help i have a 1973 coupe when i use the air cond. temp shoots up to 235 deg. car seems to run hot anyway at 210 on long drives , have new radiator water pump,thermostat, engine has been modified 262 comp cam 600 holly 370 rear end, mallory duel point dist. does anyone have a clue? let me know thank you e mail jpvcmv9@cs. com

My 79 L-82 does the same thing, but only on hot days. When I drove from Colorado Springs out to Monterey (my new home), the car really didn't like going up hills with the A/C on. I have hunted all around for an answer, and this is what I can tell you:

Corvettes retain alot of heat under the hood, thanks in part to the fiberglass. Another reason is that the radiator is canted at an angle and doesn't get the full effect of the cool air (this is what I've been told). Luckily, I have the extra cooling fan, but that doesn't really help much. What I have found is that Water Wetter works okay, and so does that cooling fan switch for L-82's that kicks in the auxilliary cooling fan at 208 degrees vs 234. That's my two cents.

Car getting hot


I have an L-81, and I had a similar problem. I removed my 4-core radiator, checked timing, water pump, and everything else; however, I found the answer to my problem from the most common and unexpected place. The gas station. In my town, there are several gas station names, but some buy the fuel from the same refinary. I was using Giant gasoline near my home at the time.

I found out from my co-worker that her Volkswagen's vapor lock problem was caused by the additives that the Gasoline companies add during the winter. Unfortunetely, all modified fuel does not get sold at the end of winter, and therefore, these companies continue to sell their fuel well into the summer. She solved her problem by switching the Gasoline vendor (she started to use Chevron). Now, this may sound unbelievable, but I solved my "over heating" problem the same way.

I wish I had the chance to try the solution before I performed all the work in my car. At the time, I found a bed of leaves in front of the radiator (apparently it deposited there during my time of residence in the San Francisco Bay area). I though surely that it was the problem cause. Nope -it wasn't! I removed the radiator again, and sent it to an expert for flushing, repairing, pressurize, and test. It did not solve the problem. I checked the car timing and related setting. It was all good. Changed the thermostat. Nothing again. Changed the water pump. Zip, zilch, Nada! Changed oil too (I was getting desperate)!

When I found out the trick, I was open to try this "shot in the dark." I waited until the the gas tank was empty. The empty idot light was nice and bright. Then, I pumped about 7 gallons of Chevron fuel (I think that Shell is also good). I was shocked to see the temperature gauge drop in temperature from 235 to about 190 deg F. I kid you not! It all happen in front of my eyes, and I wish I had a witness with me.

Now that you have looked at all the other possible causes, and you have ruled-out temperature gauge/sensor error, yet the problem persists, then give this "shot in the dark" a change. It may solve your problem too.


2 cents 2

I have a 420hp sb that I beat the crap out of. No A/C (yet) but it runs no higher than 190 degrees. Typically runs about 180. 190 is when it's over 90 degrees ambient air, going up long uphills at low rpm.
I attribute this to:
Aluminium Griffen radiator
Dual SPAL 11" fans w/185 degree switch
Aluminum Edelbrock water pump
March extra rpm cooling pulleys
Fully sealed radiator housing (except for about a 12" peice on top of the housing to allow cold air through to the carb)
Removing the rear hood seal (allows venting of engine bay heat)
8 quart oil capacity and high flow oil pump
Fully functional and sealed air dam and valence panel
Jet-Hot coated headers
(OK maybe 6cents worth..:)

That gasoline factoid is very interesting... I guess it makes sense to be a patron of a high volume Exxon service station.
All of these posts are putting you on the right track. This is usually the result of something simply out of whack.

For example, if you tend to only run hot while moving down the road, you may have a broken, or missing front air dam. If you do not have sufficient pressure in front of the radiator it will not force enough cool air through to keep the temps down.

You may have a bad seal between the radiator and core support. This will allow the air to take the path of least resistance, bypassing the radiator and going around the bad seal areas.

A radiator may be plugged with leaves, dirt, pine needles, and road debris significantly reducing air flow. You will be surprised what you find lurking between the radiator and a/c condensor. Your radiator can also be plugged inside. The situation you describe sounds like a clogged radiator.

Your a/c could be overcharged causing excessive heat in front of the radiator.

Are you using a fan clutch or electric fans? A bad fan clutch will do exactly what you are experiencing.

Just get back to the basics and work your way out from there.

I like the fuel post. I have never had hotter temps, but sure have had performance problems from poor quality fuel. Sounds like a cheap quick way of fixing the problem if that is it. It may be worth a try.

Let us know what you find.
Yeah! Me, too!

My stock 78 L48 had the same problem. I updated the AC system to run the R134 coolant and couldn't use the AC because the temp would climb to 240 degrees. So, I had just dumped a lot of $$$ into the 78s AC...and didn't dare use it...so I didn't use it for several years. I only ran it for short times periodically to keep things moving.

I have been using it more often here in Georgia, at backroad speeds of 45 or less, and it has performed fine! However I've never driven it longer than 20 minutes with the AC on.

I wonder....if my California driving at 70mph was a problem?...or if in the several years between then and now, enough over-charge has bled off?...or if even the gasoline I am purchasing at a high volume station are the contributing factors?....What an odd idea, but if it happened in front of your eyes....Man, you can't doubt that! Amazing.

We replaced the "modified" fan shroud to a complete one (orig had been cut to make room for the fan blades due to a broken motor mount before we purchased it) and replaced missing radiator seals. I'd love to come up with an idea to get more air flow under the hood flowing around the engine, but I don't want to cut my fenders or hood to install vents.

Water wetter also cut my temp by 10-15 degrees in WA state. Start with the pocketbook friendly fixes first, then delve deeper. Usually youcan find the problem was a small item.

Silver aka:Heidi
Running Hot

Boy is this ever a topic that was a nightmare to me for a long time. I'll make it as short as I can, without the whole history. I bought my 62 and from the time the weather got warmer, the temp did also. I had no shroud on it so I bought one, no change. I changed the water pump, thermostat, distributor, fan, added a fan extension. When the car got up to or over 220, it would spit, sputter and occaisionally pop through the exhaust. I finally pulled the timing cover and found I could almost touch the timing chain between the cam and crank. New timing chain, new cam, very "lumpy" cam at that. New aluminum heads, rebuilt the three core radiator to a four core with bigger tubes and more of them. NO CHANGE, the popping stopped and it ran strong, but the heat was still there. I was told by a number of "motor heads" if the block was bored it would run hot, period, but I didn't want to believe it. Over the last winter I put a new block in it, 327 bored 030 over, 12 to 1 compression, Trick Flow aluminum heads with 64 cc chambers, and a host of high performance stuff. I'm running between 435 and 450 hp. Here's the part that worked for me, I put an aluminum bcool radiator in it, three bottles of wetter water and a solid aluminum fan exclusively used on oval track small blocks. I can fill my gas tank, start the car and let it idle till it runs out of gas, or take it to red line in every gear and hold fourth at 4000 rpm's and it will not go over 180. On a pleasure cruise it runs 170, with a 180 stat in it. I have buried the demon of HEAT, finally, but it took me many hours of trial and error, my biggest expense being the alum rad, but every penny of it worth while having found the right combination to get it to run where I wanted it. I hope you find the solution quickly and inexpensively, as the other members said, start with the easy stuff first, cheaper not always being the answer. Some of the people that told me I would never get it to run cool, are amazed, but believers now. GOOD LUCK:cool
A/C related heat problems

Here's just a quick tidbit on a/c related heating problems. The fact is that 134r is not even close to a perfect solution for replacing R-12, especially in a corvette. A 134r conversion, not changing the condenser, is almost sure to cause at least an occasional overheating problem. 134 runs a much higher head pressure in the system than R-12....plain english, it causes MORE heat to be released in the condenser...right in front of...you guessed it, your radiator. Some other options for refridgerent are making there way to the market place. Amoung them 401a and 401b, and a product called "hot shot". All operate at a lower pressure and release less heat. An electric fan in conjunction with your engine fan is a big help, provided you switch it to operate continously whenever your a/c is turned on. Hope this helps with some of your a/c induced heating problems.:w

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