Midyear Overheating

[Gary M.]

Good Morning! My husband, Roland and I, purchased a 1966 Corvette Coupe with a 327/300hp engine almost two years ago, and we cannot resolve the overheating problem. It seems to be getting worse with each thing we change.

When we purchased this vehicle, it had been stored in a garage for 16 years with all fluids still in it. We drove it home and began draining, cleaning and working on the car to restore it. One of the first things we did was order a new correct radiator and replaced the hoses. After running the car, we replaced the water pump. After running the car again, we replaced parts in the distributor. We have now had a major problem with the engine, and don't know if that has anything to do with the continuing overheat problem, but the engine has now been replaced with an ATK 327/300 rebuilt.

We have spent the entire time with this vehicle, trying to resolve this issue. At one point, we borrowed a heat sensor gun and it shows that the sending unit and gauge (both of which have been rebuilt) are off by 20 degrees.

PLEASE HELP!! We are at the point where we need suggestions on anything that might help us resolve this.

Thanks for any and all directions. Pat & Roland Konter NCRS #18478

Please reply to the Konter's at mpok68v@earthlink.net

[Kevin #38315]

Re: Midyear Overheating

Pat and Roland,

You need to post a LOT more information for us to help you out on this one! What are the symptoms when it overheats? How long does it take to overheat? Does it overheat if you just let it sit and idle? (and if so, how long would that take?) Does it overheat while driving? Stop and go? Expressway? Does the heater core blow hot air when the engine is hot? What is your definition of "overheating". Does it boilover and lose all (or a lot of) the coolant when it "overheats"? How hot does the gauge run? Do you know what thermostat it has? (or even if it has one at all?) Do you have a known-good radiator cap? Are you running any kind of anti-freeze mixture?

Why did you replace parts in the distributor? Are you comfortable that the timing is back to stock (or some other known-good setting)?

How does it run when it's not overheating? surges? hesitation?

Kevin

[Bud Landacre]

Re: Midyear Overheating

If you run out of other ideas you might consider this. several years ago I installed a rebuilt water pump on my 64' Cutlass convertible and shortly thereafter began to experience overheating. I noticed what appeared to be a low flow rate in the radiator tank and, after checking the thermostat etc., pulled the water pump and found that the impeller was slipping on the shaft. Bought a NEW pump, problem solved.

Bud Landacre
62' 340 HP

[Jim T.]

Re: Midyear Overheating

Scoll down to find Les Jacobs post on Mon 15th Sep and read. You can check the archives for his posts. I believe he had replaced coolant parts like you, but the distributor gear correctly installed solved the problem.

[Mike McKown]

Re: Midyear Overheating

If you really think, correctly installing the distributor gear on the shaft fixed "Any" overheating problem you are living in LA LA Land.

[Kevin #38315]

Re: Midyear Overheating

Wow, that was kinda harsh!

I agree that it won't fix "Any" overheating problem, but he said "the problem, and it could address a problem that was caused by an overly-advanced timing issue. This would not necessarily be the distributor gear, just the fact that the timing is not correct

Kevin

[Duke W.]

Re: Midyear Overheating

Incorrect total idle timing, usually too little rather than too much, is a very common cause of overheating at idle and low speed driving. Total idle timing is the combination of initial plus full vacuum advance and may include a few degrees of centrifugal on SHP engines with agressive centrifugal curves.

Total idle timing for 300 HP and equivalent medium performance engines should be in the range of 20-25 degrees and SHP engines 25-30. Also the vacuum can should be pulled to the stop at 2" less than typical idle vacuum.

Overheating can be caused by a malfunctioning vacuum advance or one that is not appropriate to the vacuum characteristics of the engine. Installation of a high performance cam without changing the vacuum advance to one with more suitable specifications is a common error that can lead to overheating due to insufficient total idle advacne.

Duke

[Joe C.]

Mike.....I Agree With You Fully...................

I am getting tired of this "overheating" subject. First of all, what the hell do folks mean by "overheating", is it boilover, or just the temp gauge going past the "acceptable" limits. How and when does it happen? I challenge anyone, to idle their midyear smallblock (never mind MK IV engines--they are notoriously much worse)IN PLACE (that means not moving), in ambient temperatures in excess of 80 degrees (Farenheit). NEVER MIND WHAT YOUR TEMP GAUGE READS, because it is probably wrong anyway. I don't care how old or new your water pump, radiator, rad cap, fan clutch, hoses, tstat, coolant , etc, etc, is. Assuming that everything is brand new, correct, in perfect working order, no head gasket leaks et. al, timing "map" is nominal............then I say that the engine will not run under these conditions for more than 60 minutes before it boils over. This is NOT TRUE of newer cars. My 1985 Vette can idle ALL DAY like this, with no boilover. It still has the original coolant, pump, tstat, belts, hoses, rad, etc etc etc. The point that I am trying to make is, that these old warriors were made to go fast. There were not too many traffic jams back in the old days, so, the engineers DID NOT overdesign the cooling systems to account for prolonged idling with no forward motion.

Listen, I don't know much, but I wish someone would provide some empirical evidence to make a believer out of me. If I am wrong, I am not afraid to admit it. I believe that lots of folks are expecting their antique cars to act like modern day, computer controlled automobiles.

I am over 50 years old, but old enough to remember many a traffic jam on the Long Island Expressway, in the heat of summer, where I would see scores of cars, of all types, on the side of the road, hood open, steam bellowing out from below. I remember my dad telling me, "if the engine starts to get too hot, open the windows, put the heater on, full blast, and put 'er in neutral whenever you can". Never mind "turn off the air conditioner"-----we had no air conditioner, and neither did anybody else. Only thing we had was a torpedo, filled with ice, latched to the passenger side window, to force cold, humid air into the passenger compartment, much the same as NASCAR drivers are cooled today.

This is a long post, I know, but I am earnest about this.....I would really like to get to the bottom of it. Somebody, make a believer out of me.

Joe

[Kevin #38315]

Re: Mike.....I Agree With You Fully...............

We haven't gotten anywhere on this subject, because the original poster is having trouble getting web access to the ncrs site. I emailed them directly (as their original post requested) and found that out. I hope they will post more data so we can understand the real issue and suggest troubleshooting directions.

I can't speak much of the C2 series, but if you extend that to C3 (70, in particular), I'll take that bet. Until yesterday when the water pump blew a seal, I had not seen any indication of raised temps no matter what I did or how long I idled. I can't say for sure that I've idled it for an hour though - yet. I do agree though, that cars today have much better control over idle quality and temperatures.

Kevin

[Wayne W.]

Re: Cool It

I am as tired of this subject as anyone , but a new C2, with all new and correct components ,would have had no trouble with an extended idle. It would operate in the same ranges as a C4. The only advantage that the new ones have is a forced electric fan. If you think that cooling system is over designed, think again. It is operating in the range of 195 to 226 where the fan comes on. All this has done is move the acceptable temperature up and increase the differential between it and the outside air. When a C2 or C3 gets that hot today, the owner has already had a heart attack and notified this forum.