C2 Big Block overheating

[John Burke]

I recently purchased a 1967 427/435 roadster. The car is in very nice condition having previously undergone a thorough frame off NCRS restoration, it also still has the original engine and drivetrain. I really would like to drive the car a little but am concerned with it's tendency to run hot. It's like a shark, fine as long as it's constantly in motion, but seems like it could get terminal if it's stopped for too long. It runs about 190 while in motion with ambient temps around 70 yet heats up to 220 after a few stops at traffic lights. I notice the gauge looks like the yellow "warning zone" begins at 235 and the "red zone" is just below 250. That sounds kind of high to me.

I don't mind making a few minor modifications to make the car safer to drive while keeping all original parts). What suggestions can the board give me to help the car run a little cooler? I've seen electric fans on Paragon's website that fit between the radiator and engine mounted fan, also full aluminum radiators as well. Do those do the trick?

I'm also thinking of adding a set of bolt-on wheels w/ red-line radials for general driving around and keeping the original wheels and repro bias ply tires for shows.

Are there any good tips out there to make a C2 BB a little more user friendly for occasional driving?

Any advice is most appreciated.

John Burke

[Wayne W.]

Re: C2 Big Block overheating

Does it cool back down again after it has been hot? If so, it sounds like a bad fan clutch or shroud seals. Not enough air flow.

[Joe L.]

Re: C2 Big Block overheating

John-----

I agree with Wayne; the first thing that I'd look to would be the fan clutch. Your symptoms are classic for a bad clutch, although other things could also cause the same symptoms. I would replace the fan clutch with a GM #3916141. There are better and more efficient fan clutches, but none will adapt easily to your application. This one is the best of those available, can be directly installed, and looks very much like an original unit.

As Wayne also mentioned, the seals are very important, both the radiator-to-support and the radiator-to-shroud seals. To improve the cooling performance, I'd recommend using the 1968 big block seals. 1968 added a few additional seals over 1967.

One problem with 1965-68 big blocks is that they used relatively inefficient fan shrouds. There's not too much you can do about that.

[Duke W.]

Re: C2 Big Block overheating

All L-72/71 have ported vacuum advance.

Convert it to full time by either teeing off the choke vacuum break line or if you are handy by modifying the vacuum advance passage inside the carburetor (search archives for more info and testimonials from other owners). For L-71 you MUST ALSO CHANGE the vacuum advance control to a NAPA Echlin VC1765, VC1808 or equivalent, which provides 16 degrees at 12" manifold vacuum. The OE L-72 VAC is okay because it it already a 12" VAC. The OE L-71 "201" VAC requires 15.5", which is less than typical idle speed vacuum of 14", so the advance will not be locked on the full amount at idle speed, which can lead to idle quality/stability issues due to varying idle timing.

You should also notice at least a ten percent decrease in fuel consumption, especially in-town driving, when you switch to full time vacuum advance.

Other advice to check fan clutch and shroud seals should also be followed.

The fan clutch is easy to qualitatively test. When cold you should be able to turn the fan by hand with little effort. Immediately after shutting it down when it's very hot, it should take much more effort.

You can also conduct a "dynamic" test.

At low temp (before the engine fully warms up, rev it to 3500 with the hood open using you hand to open the throttle and get a feeling for the air flow and fan noise.

Repeat the test when the temperature is very high, and you should feel/hear a big difference. At low radiator exit temperature, fan speed is limited to about 1500, but it won't slip until about 3500 when radiator exit air is high enough to tighten the clutch. The fan clutch thermostat keys off radiator exit air temperature.

If you determine that the fan clutch is not performing to spec, it is better to get it rebuilt than purchase a new one as the new ones are designed to work with 195 degree thermostats (and they also have somewhat different appearance), and clutch tightening temperature is higher. Since good rebuilders tend to take a long time, you will probably want to install a temporary fan so you can drive the car while awaiting the clutch rebuild.

Duke

[Guest]

Re: C2 Big Block overheating

You might also try adding a couple of bottles of Water Wetter to your coolant. Also, do you have at least 50% water in your coolant. Water dissipates heat better than antifreeze.

[Duke W.]

Re: C2 Big Block overheating

The merits of various additives have been fully vetted in the archives, and the engineers on this Board, which includes several with OE experience universally agree that supplemental coolant, fuel, engine oil, transmission, and axle additives are totally useless and unecessary if you use the correct modern fluids. The one exception is the friction modifier additive for Positration axles.

I recommend a modern HOAT antifreeze mixed 50-50 with distilled water to replace the OE IAT blend. The most readily available is Zerex G-05, which is the same blend that is OE on Ford and DB cars and trucks.

Duke

[Richard S.]

Re: C2 Big Block overheating

John,

Follow Duke's advice and switch the vacuum can and T off the vacuum line for full vacuum advance....man, what a difference it made in my 435.....