emdoller

SWCDuke

I'm not aware that the Harrison Division of GM ever made a "copper" radiator for small block C2s. All were stacked plate furnace brazed aluminum that offer about 30 percent greater heat transfer than a same size copper/brass radiator. There have been cases of SB overheating with aftermarket copper/brass radiators that were solved with the DeWitts aluminum radiator that is an exact repro of the original.

If your B20 VAC is functioning properly and connected to a full time manifold vacuum source total idle advance with 8 initial should be about 24, but if it was originally a K-19 car, vacuum advance is ported, and if it's K-19 and Powerglide it's a really weird spark advance map that would certainly cause hot running and detonation with 8 initial.

If the engine has a non-OE equivalent aftermarket high overlap cam, the B20 may not be sufficiently aggressive. Normal 327/300 idle behavior is 500 @ 18-19" idling in neutral with a manual trans. Powerglide should idle at the same speed in DRIVE with a few inches less vacuum. If AC idle speed should be set at about 500 in neutral with a manual trans and Drive with PG with the compressor engaged and manifold vacuum should be at least about 14". Without the compressor engaged idle speed with be about 100-200 revs higher with an inch or two more vacuum.

You need to give Tom DeWitt a call.

Duke

MikeM

No doubt slower timing will result in more exhaust heat but consider the '66 327/300 Calif. timing. 4* retard on initial timing at idle. That's about 12* less than the 49 states calibration. Maybe this is why the Owner's Manual was revised to reflect temperatures the OP reported and why the temperature gauge face was changed for '66? Shouldn't affect 49 states calibration though.

SWCDuke

That particular spark advance map only applied to the 300 HP engine with K-19 and Powerglide. Total centrifugal was 40, so at 4 ATC initial, total WOT advance is 36 @ 5000, and it had caught up with the standard centrifugal curve at about 1500.

I always recommend that this weird centrifugal be modified to the "normal" amount of 30 with 8 initial, and install lighter springs to bring in full centrifugal not later than 3500 instead of the OE 5000.

I've never understood why the 300 HP K-19/Powerglide configuration had such a weird spark advance map. Automatics generally have lower "engine out" emissions because manuals generate a hydrocarbon spike when you lift off the throttle to shift. It would have made more sense to have that weird map on manuals, but it was early in the days of emission controls and the engineers were still low on the learning curve.

Duke

MikeM

I know what it applied to and I suggested that instead of making a California supplement to the Owner's Manual, GM made the manual cover all combinations and changed the gauge face for the same reason.

The tune-up chart I just looked at says it's for manual and auto, both '66 and '67 model years. Don't know if that's true and it's been too long ago to remember.

The point is, some midyears left the factory with severely retarded timing at idle speed which is the speed the OP is complaining his engine is running too hot. So if retarded timing is all that important relating to overall engine cooling, then one could expect only the California engines to suffer and not the 49 states engines.

For my part, I have run the old dual point Delco distributor 200-250K miles in different cars with no problem of overheating . Never in a Corvette though..

SWCDuke

There's a simple test you can do. When cold, engine off, you should be able to turn the fan very easily with your finger. When really hot shut down the engine and it should take considerably more force to turn the fan. When cold the fan should not turn more than about 1500 RPM, but when really hot it should go to about 3500, so another simple test is to compare fan noise at 3500 engine revs hot and cold, and when hot you should hear considerably more noise.

The fan clutch engages based on radiator exit air temperature. Most current replacement clutches engage at higher temperature than origina '60s fan clutches because the former are set up for the typical 195 thermostat opening temperature of emission controlled engines, so in traffic, even with a 180 thermostat a pre-emission controlled engine will run hotter in low speed traffice because the fan clutch doesn't tighten until a higher rediator exit air temp.

Duke

GTOguy

This bolded sentence is the key....the IDLE SPEED part. And what I said a long time ago in this thread about it only running hot at IDLE speed. Missing water pump impeller blades or retarded timing would cause the OP's engine to run EVEN HOTTER GOING DOWN THE ROAD. ESPECIALLY UNDER LOAD. Since this is NOT the case, and the car RUNS 180 DOWN THE ROAD, the problem, I'll say it again, is not enough air flow through the radiator core at IDLE SPEED. My bet is that if the OP lets it sit and idle and puts a big box fan in front of his car and turns it on 'HI", the car won't overheat. So, fan issues, shroud issues, etc. First place to start. Been tuning cars for awhile now, thousands of them over the decades, and it's amazing how constant the laws of physics remain.

Frankie the Fink

And the OP should not fall prey to the myth of "re-clocking" the fan clutch spring for a lower temperature engagement...it does nothing and can actually cause damage..

MikeM

I had a '65 Chevy II sedan I stuck a hopped up sb 400 in. Sometime in the mid '70's. I had a fan clutch on it and a single row, cross flow radiator in it out of a Monte Carlo. Too small, radiator even in the Monte Carlo but it worked great. That is, until, I got caught in a traffic jam during the Shades of the Past Rod Run in Gatlinburg. Any of you that have ever been there in those times knows what I'm talking about. Hot weather, Stop/go. Might make a mile in half hour.

The 400 had the old reliable dual point distributor in it with no vacuum advance. I was able to stay in line for about 30-45 minutes before I had to break out and take a side road. Radiator too small, fan/clutch too small, distributor with no idle advance, and everbody knows 400's overheat anyway.

Surely, a midyear Corvette with a factory designed cooling system can survive normal, everyday traffic without getting hot.

0Tom@Dewitt

Again, logical thinking but I still don't think it's air flow. The timing issue goes away when you start driving because the distributor weighs kick in the extra timing due to higher rpm. I don't mean to toot my own horn but this was my career, not a hobby or part time thing. You can easily cover up issues like this idle timing with bigger radiators and electric fans and some might argue that they were right it was all about air flow when it cools better. More air will make it cool better but I am trying to help reduce heat, not bandage it.

mattnSD

this fixed mine

GTOguy

Point taken, Tom, and yes, I am running one of your radiators in my own '61. I myself am not a part time guy or hobbyist. I've been an ASE Certified Master Automobile Technician for decades, and have worked in the automotive industry as a professional, specializing in drivability, since 1979. I can't even estimate the number of cars I've tuned up and repaired. I agree that, like many systems on a car, a cooling system working properly is the sum of a lot of components, adjustments, and variables. Every one of those components and adjustments has to meet manufacturer's specs. And it IS easy to 'bandaid' one or more problems by simply going overkill with a larger radiator or electric fan. If the OP has everything else sorted and his car overheats at idle, it is not dissipating the heat out of the radiator core for whatever reason. Usually, it is airflow issues with a bad fan, clutch, or leaks in the shrouding. We'll see where this one goes!

MikeM

Just a deplorable hobbyist. Not certified. Don't know much, just trying to get by..

FWIW, I used to come home at night in my '56 Bel Air with 327/340 engine in it. The exhaust manifolds would be glowing cherry red. you could chalk that up to the non-vacuum advance Delco dual point distributor I was running. Still, no overheat using the OEM '56 Bel Air radiator in the car. None!

I've found timing can contribute but if everything else is right, timing is not the deal breaker in my experience. My '65 will idle a long time with a copper radiator, 4* INITIAL and the original fan clutch on it. So, WDIK?.

I don't have a DeWitt radiator but I can certainly see the value in having one if you have a cooling problem.

MikeM

I might add that I find it hard to believe the cooling system is so marginal that a few degrees +/- on timing can cause one of these cars to overheat. Doesn't sound right to me.

Especially, when you have cars that have added air conditioning and experience no problems.

GTOguy

As a non-certified deplorable hobbyist, Mike, you certainly go about diagnosing and solving automotive problems in a professional and certified manner. I can't think of a time when I didn't agree with any of the solutions you've posted, although there may be one or two. On any thread. You approach problems with skill, logic, and common sense---based on many years of personal experience. The same way I do. Only you've been doing it 20+ years longer. Back to topic.

0Tom@Dewitt

And just like that, a career in Corvette cooling cancelled out....

Read up, good stuff

Corvette cooling

Ignition timing 101

Robert61

In the John Z article very early in it says 90% of all cooling problems are either restricted radiator flow or not enough air flow. I'll go with MikeM. And GTO Guy not enough air. I see this every year at cruising the coast where cars sit not moving for an hour or two. Not specifically Corvettes but many original restored cars that I sure got new radiators as well, pulled over on the side puking water the like a frat freshman. If they had enough air flow they would stay calm cool and collected. Which is why I have 2 pullers and a pusher.



This would be a good test for the timing suggestion. If only the op would take the advice and advance the timing 15* and slowly drive it around the neighborhood. DO NOT CONTINUE if it is detonating. Then report back with the results.

leif.anderson93

You mean the timing suggestion that was mentioned way back in post #4, by Tom DeWitt and others...yea, it would be nice. While it could be a combination of everything mentioned, this would take all of 5 minutes to try out. Too easy and time efficient, I guess.

0Tom@Dewitt

It's actually John H (Hinckley) Retired automotive engineer

and there is no need to drive the car. If the problem is a vacuum can/timing issue the car will get hotter and hotter just sitting in the driveway.

Oh, we still do not know what radiator is in there. Can we get a picture OP?

Robert61

John Z is John Hinkley!



The test is simple enough and free, all he has to do is do it.