I have a 1966 Corvette with a 327 bored over .60 and a mild cam. Factory 350hp aluminum manifold and the double hump heads. I have owned this car since 1972. It has always run on the hot side 210 - 220 when the outside air temp gets into the 80's. If the outside air temp is in the 50's the car will stay at 160 - 180 no problem with the 160 thermostat. The problem is at its worst when it is hot and I make a series of stops and shut the car off. Like bank, barber shop, store, gas station and so on the temp keeps climbing and does not want to come back even when the car moves down the road. I have the proper fan and new fan clutch, the shroud is intact and the seals have been replaced, radiator is a new copper replacement. Upper and lower hoses new. I have made some strides lately by installing an Edelbrock high flow water pump and adding some water wetter. But since the air temps have not really gotten into the 80,s too often yet here in the northeast I am not sure I have made that much progress. Is there something I am missing here? Bottom line if it is cool outside no problem. If it is hot outside the temp keeps climbing and won't come back down unless I park it.
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Re: 1966 engine temp
There have been several posts here talking about proper timing and proper vacuum advance operation. I can attest that it makes a difference. I have a 66 L79 and when I bought it a few years ago, it did exactly what you describe. It had an old, bad, copper rad in it, so first I replaced it with a DeWitt's aluminum one. That made an improvement while underway, but at stops, the temp would still climb. Fixing the vacuum advance (mine was not working) and setting the timing correctly cured the problem. It will idle all day and not get above 190. Underway, it runs cooler, around 160-170 even on an 80 degree day.
Cem Z. and Duke Williams have posted on this topic recently. I did not do any of this with my own hands, but based on their advice, I told the guy who works on the car what I wanted checked.
I think my motor is 30 over, I can't comment on what difference a 60 over rebuild would cause.
Rich Giannotti1966 L79 Convertible. Milano Maroon
1968 L71 Coupe. Rally Red (Sold 6/21)
1963 Corvair Monza Convertible -
Re: 1966 engine temp
1. Do you have a vacuum advance can properly matched to the manifold vacuum characteristics, which are determined by the cam? You select by measuring manifold vacuum @ idle speed. Does the vacuum signal line provide full manifold vacuum at idle?
2. Many aftermarket brass radiator's are known to cause hot running because they have less heat transfer capacity than the original type aluminum radiator
A 160 thermostat will not "solve" hot running condition because the thermostat establishes the LOWEST operating temperature. The highest temperature is deterimined by a combination of a proper ignition advance map, proper radiator in good operating condition, and a properly functioning fan clutch.
No amount of "high flow water pumps", 160 thermostats, water wetter, or other snake oil additives will make up for a low heat transfer capacity radiator, improper or malfunctioning fan clutch, or an ignition map not properly suited to the cam. Many replacement fan clutches are designed for 195 thermostats and don't tighten until a higher temperature than the OE fan clutch. There are specialists who can rebuild the OE fan clutch.
You are going down the wrong path. Many have proceeded you and virtually all have failed until they:
1. Installed a correct aluminum reproduction radiator from DeWitts.
2. Rebuilt the OE fan clutch so it tightens at the proper radiator exit air temperature provided by a 180 degree thermostat.
3. Established an ignition map (with special attention to the vacuum advance) properly matched to the cam. For the mild cam you mention, you need the full 16 degrees of advance from a 16 degree can at idle, which means that the can should provide full advance at 2" less than idle vacuum. This combined with initial timing should provide TOTAL idle timing in the range of about 25-30 degrees.
DukeComment
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Re: 1966 engine temp
Thanks for the new ideas. I should have mentioned that I am running a Mallory Dual Point with mechanical advance. Timing is set at 10 degreesComment
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Re: 1966 engine temp
Get rid of it, but first advance the timing to 25-30 degrees and take a manifold vacuum reading. Then let it idle at this timing and watch the temp gage. Chances are good that it will not overheat! Obtain a tach drive single point distributor, disassemble it for inspection and overhaul. If the engine produces 14" or less idle vacumm at 25-30 degrees timing as mentioned above, install a NAPA/Echlin VC1810 vacuum advance, which provides a maximum of 16 degree @ 8" and BE SURE it is connected to a vacuum source than provides FULL manifold vacuum.
Set the initial timing so that intial + full centrifugal = 36-38 degrees.
This may well solve the problem and is the cheapest issue to correct first.
Unfortuneately, it appears the "Bubba" has re-engineered your engine and completely screwed up the very good OE engineering/tuning that was accomplished by Chevrolet engineers nearly forty years ago.
DukeComment
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Re: 1966 engine temp
Dennis, in addition to the DeWitts correct reproduction, Tom is also offering a direct fit aluminum radiator that isn't quite as good as the OE design, but has significantly higher heat transfer than the copper replacements. It is attractively priced. You can get all the specs and prices on the DeWitts website.Comment
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Re: 1966 engine temp
Dennis- Duke's absolutely correct. These small blocks need plenty of advance to stay cool. They get it by throwing in lots of vacuum advance at idle and light throttle and without the advance can they go "off-scale" on temp. The only other way to keep it cool without the can would be to re-engineer the cooling system from the ground up. So "can" the Mallory.Comment
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Re: 1966 engine temp
For those who still don't think the ignition map makes a difference on operating temperature, try this test.
Disconnect the vacuum advance and set the idle speed up to an acceptable level. Let it idle until the temp gage climbs then take an IR gun reading from the exhaust manifold.
Now reconnect the vacuum can. Give it a few minutes and watch the coolant temperature come down (assuming the vacuum can is properly matched to the idle vacuum chracterisitics). Reshoot the exhaust manifold with the IR gun and note that they are SEVERAL HUNDRED DEGREES COOLER.
Recall that the exhaust ports are surrounded by coolant passages.
So you thought the idle ignition map wasn't important???
DukeComment
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Re: 1966 engine temp
Duke- AMENComment
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Re: 1966 engine temp
I have to thank all of you for your help. In 24 hours I have the right information for a problem that I have been having for over 30 years. As far as the distributor is concerned I assume that a HEI would be OK as long as I have the vacum advance. Most importantly thanks for helping me understand the problem and not just telling me how to fix it.Comment
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Re: 1966 engine temp
I don't think a HEI will fit. It certainly will not fit under the shielding.
Suggest you purchase a Delco tach drive single point distributor as I recommended previously. Since these were common to all carbureted Corvettes (ex. K-66) from '63 to '74 they are fairly common. Overhaul it and characterize the centrifugal curve and install a suitable vacuum can.
If you want a breakerless ignition, install one of the available electronic conversion modules, but IMO, especially on a car that does not accumulate a lot of miles, breaker points work just fine. They are inexpensive, reliable, and easily last 30K miles with the 1.8 ohm ballast and 202 coil. With the 0.3 ohm ballast used on SHP/FI engines prior to '65 their life will probably be shorter.
DukeComment
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Re: 1966 engine temp
Also, if you haven't already done so, "shoot" the thermostat housing/upper radiator hose with an I.R. gun and compare that reading with the temp gauge reading at the same time so you know what the gauge is really telling you. This should be cooling system diagnostic step #1 so you have a comparative baseline temperature indication to work from.Comment
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Re: 1966 engine temp & HEI
As I learned from Duke & others, the HEI will likely have different ignition mapping that may lead to other problems. I bought a '66 Pontiac a couple of years ago with many non-stock parts. It pinged, dieseled, overheated, etc etc. The HEI distributor was the biggest culprit. I tried adjustable vacuum cans and distributor springs etc. Then Duke explained that many HEI distributors were mapped with more vacuum advance and less centrifugal advance than cars of the 60's in order to meet emissions. The emission cars used ported vacuum sources and then also started adding more bells and whistles such as vacuum retard cannisters, thermo-vacuum switches, anti-dieseling solenoids etc to the carb and distributor to treat symptoms that the ignition mapping changes created. Anyway, I never did get the HEI working right. Granted I could have found someone to totally recurve the distributor, but I just ended up replacing it with a stock distributor, and those symptoms have been cured.Comment
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Re: 1966 engine temp & HEI
GM has a HEI distributor that might work. This is the same distributor that is used in the high performance crate engines like the ZZZ, ZZ1, ZZ2,ZZ3, and ZZ4. At 10 degrees initial, with its vacuum advance unit, and centrifical advance it comes out to 38 degrees. I have one in my 70 Corvette and like it enough that for the past 9 years I have driven without a tach. I use full time vacuum 100% of the time and have not heard my engine pinging on 93 preimium.Comment
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Re: 1966 engine temp & HEI
Question for Duke...
Do you routinely recommend switching from ported to non-ported vacuum to the
can for any small block of this vintage?Comment
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