66 small block getting hot in traffic

[Edward S.]

Here's the scenerio. Just installed a DeWitt repro radiator, rebuilt the water pump, new thermostat, shrowd is in place, flushed and installed the Havoline long life coolant. Here's the problem. I sat in traffic last Sunday for 20 -30 minutes. It was 85-90 degrees in NY. The engine did not overheat but seemed to be heading there. The temperature gauge was just about there when traffic moved along. The temperature almost immediately went down to about 210 when traffic started up. Within 1-2 miles the temperature was normal. The fan clutch appears to be working properly. Is it the nature of the beast? Could it be the fan? Fan clutch? should I remove the fan clutch? Would that help???? Any input would be welcome. Thanks Ed Sullivan member # 30327

[Bill Lucia]

Re: 66 small block getting hot in traffic

Ed, I have a very original 66 big block coupe that does NOT overheat, even in traffic. The only thing that you might check is the temperature sending wire. Is the cover on the wire all in one piece? Also, about one or two years back there was an article in the Restorer about a car overheating. If memory serves one of the fixes was to have the carb adjusted!!!! Sounds crazy but it worked. I don't recall who wrote it (maybe Bill Sangrey??? he has 63's). You might search for that article I know it's out there...

regards Bill

[Joe L.]

Re: 66 small block getting hot in traffic

Ed------

The "overheating in traffic" and "cooling down at road speed" sounds an awful lot like a fan clutch deficiency. I don't recommend ANY aftermarket fan clutches, especially the "non-thermal" variety. Quite frankly, I consider even the GM replacement fan clutch for your application, GM #3916141, to be marginal with respect to cooling efficiency. It is, however, the best unit available which directly services your application. The condition of these units is very difficult to accurately assess, so if yours has several years of use, you might want to replace it. Unfortunately, these units aren't inexpensive. This one currently GM lists for $157.48.

To be honest, my preference as far as fan clutches go is the 74-81 A/C fan clutch, currently GM #12529342. This is absolutely the best fan clutch that I have ever used. Noisy, but IT DOES MOVE SOME AIR. Unfortunately, you won't be able to use it with your stock '608' water pump.

[Dale Pearman]

Re: 66 small block getting hot in traffic

What's the matter with a new pulley that overdrives the fan by at least 10%?

Varooom!

[Duke W.]

Not a good solution

The cooling system design on the small block C2s was well engineered and should perform well if everything is in proper working order. This car has a problem somewhere and redesigning the system because of a faulty part is not a very efficient way to repair a system. If it was a "design error" then an engineering solution is called for, but I don't think that's the case here. Does anybody know of a simple fan clutch test?

Also, check that the initial timing is set properly and the distributor has the correct vacuum advance that is functioning properly. On a '66 the vacuum advance should be ported directly to manifold vacuum and full advance should be evident at idle. Idle speed and fuel mixture should also be checked that they are within specification.

Duke

[Craig Nicol]

Re: 66 small block getting hot in traffic

20-30 minutes of idling in traffic is probably pretty close to the limit for any 60s corvette, in my experience. Make sure the timing and carb adjustments are proper. Excessive fuel and/or retarded spark will cause hotter running. I have had excellent results in problem cars using an rpm limiting fan clutch. The thermal clutch doesn't drive the fan hard until high air temp off the radiator activates the clutch. In my experience, Idling corvettes with free-wheeling fans don't always activate the fan clutch. The RPM limiting clutch drives hard until the fan reaches a specific RPM (like 2000 rpm for example) then they start "slipping". This allows strong airflow at low speeds. There is a trade-off though. Fan noise may be objectionable. NAPA number 263325 as worked well for me, allowing my customers to participate in parades and cruises where they couldn't before the change. These list for under $45 and can be installed and returned to stock in minutes. JMHO, Craig

[Wayne M.]

Re: 66 small block getting hot in traffic

Ed --- Agree with others that the situation you described is common to a C2 at its best. If in the same situation again, I'd turn the heater on max to remove some calories from the coolant, and keep the motor at about 1200 rpm to help move a little more air. You can "test" the GM coil-type fan clutches by releasing the coil end from the anchor pin and rotating the plug (I think it will only go one way); this "tricks" the clutch into maximum engagement, irregardless of ambient temp. The latest "141 ?" GM clutch has a higher coil calibration than was used in the '60s, so it is not really the exact replacement. There are articles published in the RESTORER and in the archives (by Fred Olivia, among others) on the clutch aspect of overheating.

[Dale Pearman]

Re: Not a good solution

Worked just fine for me with a C1 and an increase from 327 cu in to 410 cu in.

Varooom

[Jeff]

Wow! Changing the pulley size did all that?

...and to think all these years I've actually been boring my stuff out to increase the displacement. Damn. What size pulley would I need to get my 283 out to 8 liters, Dale?

JP

[Dale Pearman]

Re: Wow! Changing the pulley size did all that?

Such large displacements would require a double groove pulley. Suggest you check out Mack trucks for correct part. Varooom!:D

[Dave - NCRS#24235]

cheap tests on a 66 small block getting hot

Cheap tests: Remove the fan clutch (save it for shows). If possible, replace it with any junk yard spacer that fits (to insure the fan is in the shroud). If you have a nonstock radiator, you may have to add air conditioning radiator seals to the car. Does the car have air-cond? If so, you MUST have the seals. Is the idle at least 700? If you squeeze the lower radiator hose and it collapses, the spring inside has rusted out, and the pump will suck it flat. Did you check the radiator cap? No pressure means no cooling. Test for a 180 degree thermostat by throwing it into a pot of boiling water (even new ones have been known to stick). Make sure the thermostat IS a 180 degree and not a 195 (run without it as a test). P.S. If this car has air-cond or powerglide, tell us. - Dave

[John Fleming]

Re: 66 small block getting hot in traffic

I was reading Ed's post, and was wondering what temperature is considered normal when the outside air is 85-90 degrees. I have a 1963 340HP, and it was running a little above 180 when driving, but around 210-215 when sitting in traffic. Is this normal?

[Robert C.]

Re: 66 small block getting hot in traffic

I would think, that at 90d. temps,you can't expect a car to run 180d. at speed and then expect any less than 200-210 at idle. The first example in this thread was a car sitting for 20-30MIN. at stop in 95d. heat! You guys go try that test, and let me know what your temp gauge reads after 30 min's. I'll use that info in my current "Overheating in southern climates" survey!! Thank You in advance. Bob


NCRS-Texas Chapter

[Dale Pearman]

Re: 66 small block getting hot in traffic

Corvette temperature guages are not to be trusted. When she spits coolant out of the overflow, she's too hot. That's all! Install a mechanical thermo-meter that works, like a Stewart Warner, temporarily if necessary, and find out what's going on. The vette guage is accurate at one point only. The rest of the scale is highly non-linear!

Dale.

[Martin M.]

Re: 66 small block getting hot in traffic

MY '63, then living in Massachusetts, had the temp while cruising slowly rise from 180 at the beginning of summer to 195 at the end. Moved it to Las Vegas, and figured I was in for some work, as the temp here is over 100 every day from June thru Sept.

However I decided to try a cheap solution first, and installed a 180 'extra performance' thermostat from Robertshaw #330-180. I have used these before with excellent results (lowered the temp 10 degrees in my dually tow rig). The temp immediately returned to 180 and never wavers at speed, or idling on the Las Vegas strip. Summit racing used to have them in the catalog, and my local Auto Zone has them on the shelf. Seems almost too simple, but they cost only 7$. What have you got to lose?

Marty