My 66 300 HP with Powerglide and a brass radiator will creep up to about 210 at a long light and a hot (85 F or above)but will gradually come back down with speed. There are a couple of things you can do to improve (but not eliminate) the problem for all the reasons mentioned in the other replies. First, install a 160 degree thermostat. This won't correct an under cooling capacity problem but will give you more room in an overheating situation. Since you drive daily condensation in the engine will not be a problem with a lower temp thermostat. Secondly, most road and circle track racers use a product called Redline Water Wetter. This is a surfactant that improves heat transfer from the block to the coolant. Remember that a large portion of the heat in an engine is removed by the oil as well as the coolant. In a Nascar engine, tests have shown a 10-15 degree drop with no other changes. Thirdly, stock water pumps have a stamped impeller. A few have a cast impeller. The cast impeller will run cooler (10 degrees or so) but you can't tell without removing the back cover. There is an aftermarket kit that is basically a disk and pop-rivets that are attached to the back of the impeller and close the back improving its efficiency at low speeds. Most of the racing suppliers (Summitt, Jegs) have Water Wetter and the kit for the pump. Since it is only a driver, consider replacing the stock fan and clutch with a flex fan and 2-in. spacer. This is only four bolts and is easily returned to stock in cooler weather and at shows. For correct operation the blades should be 1/4 in and 3/4 out of the shroud.
-
-
Re: Overheat at idle 67 300 H.P. automatic and A/C
Many thanks to everyone who have contributed suggestions with this problem.
I will install a new radiator, eleectric fan, and high volume water pump.
Suggestions regarding the best available set up will be greatly appreciated.
I've also neglected to say this vehicle will overheat with the A/C on while at highway speed.
The decision to restore and drive this vehicle daily (rather than buy a new Corvette) is still my preference. I'm willing to do whatever it takes to be able to drive it in all conditions with all options working properly.
There were a number of vendors a Carslile last year offering high-tech radiators. Does any one have any suggestions?
I'd like to get this problem squared away immediatly! -
Re: Overheat at idle 67 300 H.P. automatic and A/C
Paul, before you go to any unusual extremes just remember that the way that GM sent these cars out to be daily drivers has worked for years: alum. radiator, stock cooling fan, and 180 degree (?) thermostat. I had overheating problems in my 66 with a 327/350 until I installed a DeWitt reproduction Harrison radiator. You might want to check out their web site, listed below for a comparison of the four types of radiators available for your Corvette. I ordered mine and got the show price, although NO ONE will ever say these are cheap. I can now run all day long at highway speeds with 90 degree outside air temps with no problems.
Gary 21316Comment
-
Re: Overheat at idle 67 300 H.P. automatic and A/C
Paul,
I agreed with Gary. My 66 Auto was having similiar problems to your. Once I took out the brass radiator and installed the new Dewitt aluminum, I have had no more overheating. The NDB convinced me that the Dewitt was the most correct and comes with a 5 year warranty. They are not inexpensive though!
The aluminum radiator's volume is much greater than the brass. I know this because I had to add additional coolant upon refill. I also went to the 160 thermostat and now sometimes I think it stays to cool.
Good luck,
Gerald Lee #31112
Ebay 73 Sales CatalogComment
-
Re: Overheat at idle 67 300 H.P. automatic and A/C
Thank You Gentlemen. I will order one immediatly.Comment
-
Re: Thermostat / Restrictor, final pitch
Paul,
I came in a little late on the thread, but posted something about the thermostat / restrictor idea at the end of your original message.
Studying the messages and responses you've received, I agree that your original factory set-up, the small block with A/C and A/T is one of the most heavily taxed cooling systems to come off the line. More than likely yours is functioning as is, at it's best already, as original and as pointed out by others.
Replacing what you want with new products I have no doubt will reduce if not elimate your overheating situation. What I mentioned about the restrictor kit I've believed can be a benefit in situations like yours where the cooling system is most heavily taxed. My own situation was to mostly reduce high temperatures at highway speeds in a shark-bodied car with 427 and 4:11 rear gears. Using one of the sized restrictors in a flow restrictor kit has taken the edge and top-range of high temperatures out of my single problem. And I'm not promoting the restrictor as an overheating "cure-all" for all cooling problems. But it may be the one thing that you can or need to "adjust" for your heavily taxed cooling situation.
I just thought I'd mention it again for two benefits, an attempt to preserve your original functioning factory cooling set up, as well as saving to have to go to the larger expense of replacing radiators and other cooling components. Best of luck with the problem. TBarr #24014Comment
-
Re: Thermostat / Restrictor, final pitch
Tom--
Thanks again for your extra effort. I appreciate your suggestion.Comment
-
Re: Thermostat / Restrictor, final pitch
Tom, Do you remember which of the restrictors you used. Small, medium, or large opening. Did you test all 3 sizes in the kit? Does it only help at high RPMs on the highway? or? Bob
Texas Chapter NCRSComment
-
Re: Restrictor, some results (long)
Bob,
I had tried all three and settled on the largest opening, which is an inch in diameter. The two smaller sizes have a 5/8" and 3/4" diameter opening. The 5/8" restrictor didn't seem to have any better effect than my regular 180 degree thermostat. The 3/4" ran slightly cooler temps, guessing by my gauge something around 10 degrees difference or less.
The one inch opening had the best effect and took off the high-end of my engine temps, which for the most part now are usually below but don't get past 210 while driving. Once or twice it ran over 210 late last summer, but I remember I had the car out (on and off the highway and around town) for at least a couple hours straight. Not bad, considering my "old" temps ALWAYS ran up to a good 220-230 each time. With the restrictor, around town (stop and go) it's the same for me, usually below 210. In my case, with a 4:11 rear, it does depend how much I stay out of the higher RPM's. The engine temp will still go above the 210 if the engine is hot then I sit and idle for longer than about 5-10 minutes. But it's nothing like it used to be.
The biggest difference I see is in cooler weather. If the ambient temperature outside is below 70 degrees, then while driving there are times I don't see my engine temp run above the first "hash" mark on the gauge, maybe 160 or so. I should probably run a thermostat at that time of year.
It seems a little surprising how the small difference of each restrictor opening-diameter can make such a difference between them in engine temp. If you're wondering why not just use "nothing" (no restrictor or thermostat) then I would say that I've never really seen it recommended anywhere in print. Some of the most recent cooling articles I've seen highly recommend to have SOMETHING in place, either a thermostat or a restrictor. I haven't been a real proponent to "push" the restrictor as a "cure all", but I think it's application can at least be used for a heavily taxed cooling system, maybe more. For $7-8 bucks I've figured it would at least be worth a shot if someone is willing to try anything. TBarr #24014Comment
-
Re: Overheat at idle 67 300 H.P. automatic and A/C
Hi Paul:
I am very impressed with the effort you have gone through to rectify your problem. You are well read and knowledgable, I hope your patience is rewarded and you have a cool summer.
jerComment
Comment