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My 77 L48, A/T still gets really hot after driving about 20 miles. It gets up to around 240*. I replaced the radiator, all hoses, belts, water pump, cap, thermo housing, 180 thermo. If I turn on the A/C it gets even hotter.....any suggestions?:confused
77, Have you tried a "real" temp gauge. Try a guage from a parts store. Just install it where the sending unit is(Left head). Compare the real guage readings with the car's. These things are notorious for being wrong. Also, somthing else you might try is removing the thermostat and see what happens.........Steve
Have you tested the clutch fan to see if its working???
1) verify the gauge is reading correctly.
2) make sure the radiator is clear of debris
3) make sure the radiator is not restricted or plugged
4) make sure the stock fan shround is intact.
5) make sure the fan clutch is functional
6) you must have the stock air dam or "lip spoiler" in place.
ccflorida....how do I test the clutch fan to see if it's working?
checking a fan clutch

Hi 77vette,
To check the fan clutch when the engine is cold and not running, you should be able to spin the fan blades freely with no resistance. After driving the vette so it heats up, the fan clutch should engage (temperature activated) and be firmer, turn the engine off and it should turn with resistance, but not spin freely.

As I also understand, when you turn your engine off (hot) with the hood up, watch the fan blades, they should spin several revolutions before stopping. It should not stop instantly when the engine is turned off. Will someone please correct me if this theory is wrong?...

Hope I was helpful.
I switched to a flex fan and cured my running hot woes, and I had done everything you had previously done to yours, also. You could check out the "Flex Fan" post in the C3 section for my findings.

Silver (Heidi)
Thanks Silver., I checked the fan clutch as you mentioned ,it seems to be ok. I'll get a real temp gauge as others mentioned and see where that's at. I haven't tryed water wetter yet. Maybe that will help before I invest in a flex fan. Thanks for input you all...;)
water wetter

I tried that product in WA last summer and it really did work! It did not solve my running hot temps under all conditions, but it did keep it cooler under normal driving conditions.

I heard somewhere, can't remember where, that water wetter works because it inhibits air bubbles forming in your cooling system. Is this true?

I was told if you tie a piece of string (nothing heavy duty) to the fan blade and start the motor if the string breaks the clutch fan is ok also check the fan after you make a short trip with the engine running ,the fan should be turning when you check it..Good Luck

Check and see how the radiator is flowing. Empty some of the fluid out till you can see the tubes. Check to see if you timeing is set too advanced. Check you Idle mixture, if it is too lean the this can cause overheating. Check to see how cloged-up your A/C condenser is. Scrap the old fan and go with a FLEX fan and spacer.

Man, I know these are difficult problems to troubleshoot!
New Radiator

I was experiencing high engine temperatures when running for extended periods at 55 mph or above in 90 degree + weather. The local radiator shops wanted $100 to clean the radiator tubes and $220 to recore the radiator. I shopped on the Internet and found a larger capacity (+33% over stock) new Wolverine radiator for $153 - delivered for free - overnight by FedEx. I have installed the radiator and once the vehicle is warmed up, it is now impossible to get it higher than the rated thermostat.

As info.

Portland, Oregon

Make sure youre radiator sides are sealed well. Power wash front and back of radiator and condensor - spray them with simple green first.

Hows the lower radiator hose ? Rev the engine to 3000 rpms while standing still, and see if it is collapsing.

Use no more than 25% coolant to remaining distilled water with a bottle of water wetter.

For temporary fix, take out your thermostat and/or, leave your headlights popped up for increased airflow to radiator.

I assume you have thoroughly cleaned the cooling system with Prestone H.D. Cleaner and flushing Tee, including opening all block drains and radiator drain valve ???
Let us know the outcome. Good luck,

Roy!! Please provide more information as to where you got your Wolverine Radiator. Do you have a web address for us?
Purchase of Higher Capacity (4-core) Radiator

The Web site that I ordered the Wolverine 4-core radiator (the stock radiator in my 78 was a 3-core) was:


They can also be reached at 1 (888) Radiator

The part number is 718 and the Web price is $193. Radiator.com has a 110% meet&beat-it guarnatee, so I shopped around and found the same radiator for a lower price at:


Speedy radiator had the same 4-core radiator, their part # SRP 718, for $170. With this information, I again contacted Radiator.com by sending an E-mail to help@radiator.com

After a bit of discussion, Radiator.com agreed to sell the radiator for $170 less 10%, or $153. The radiator was shipped FREE on FedEx and arrived the next morning at 10 a.m.. The radiator works great!

Hope this helps.

Portland, Oregon
Thanks for the info Roy!! The overheating problem in my '75 is almost licked . . . the last link in the chain will be a 4 core radiator. Being a working stiff, I appreciate any price advantage that I can get.

While I'm here, I might add that the biggest problem with my vette was overheating after running for long periods at freeway speeds (65-70). As soon as I slowed down, it would begin to cool off. I discovered that the engine was running a little lean at speed. After I richened it up a little, it still runs a little warm (210-215), but it doesn't continue to climb into the danger zone as before. This with the stock fan . . . after all, the fan really does not do much where cooling is concerned when running at high speeds.
I fought the overheating problem for several years with a highly modified engine. More power, more heat! Went with the flex fan, high flow pump, redline water weter, big block radiator, ect, ect. Everything seemed to help a little to keep pushing it to a cooler temp. Probably one of the biggest things was a tip I read in a vette tip. Remove the thermostat and drill a small hole in the body, I think it was like a 3/32, and it keeps a small amount of coolant flowing continouly. This caused a noticable difference. My next step was headed to a high dollar custom aluminum radiator but so far I have avoided it. If you remove the thermostat completely all that will do is stop the coolant from being able to cool down in the radiator and it will actually run hotter in that the coolant is continously circulating. We used to try that years ago in the old rods and it never worked out in the long run. Of course most all of them run hot in hot weather in the city with the a/c going. Keep trying and you will eventually get it right.

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