I Dare Not Use the C-60 When it is Hot Outside

[Clark K.]

I dare not use my factory A/C when the car is in traffic or if the air temperature is over 90 degrees. I have been told by numerous sources that cars like mine will never keep their coolant/engine cool (under 230 degrees) when running the A/C under those conditions. Some have told me that Chevrolet made a big mistake putting A/C on the L76 engines. I find this statement incredible since A/C was an option for the big block engines.

I have had experts set and reset the ignition timing until I am sick of paying for it. I have changed to richer carb jets, replaced the fan clutch, checked my 7-bladed fan, changed to a new DeWitt's aluminum radiator ($900), changed thermostats, checked for collapsed hoses, IR'd the various spots, etc. to no avail. I have done everything that this forum has suggested except change out the water pump or dismantle the engine.

I want to keep my car "NCRS Top Flight" original to do well in upcoming regional and national flight judging. So, I am reluctant to do anything at this time that would make my car appear less correct. So, electric fans and a larger radiator is not in the picture.

But, I noticed in the Long Island catalog that for a 1966 small block with A/C, there are upper and lower radiator "seals" listed (sec. #26). Other than these seals being incorrect for a 1965 (according to the catalog), would the installation of these '66 upper and lower radiator seals help my car run cooler with the A/C on, in hot weather? What say you experts out there?

[Joe L.]

Re: I Dare Not Use the C-60 When it is Hot Outside

I dare not use my factory A/C when the car is in traffic or if the air temperature is over 90 degrees. I have been told by numerous sources that cars like mine will never keep their coolant/engine cool (under 230 degrees) when running the A/C under those conditions. Some have told me that Chevrolet made a big mistake putting A/C on the L76 engines. I find this statement incredible since A/C was an option for the big block engines.

I have had experts set and reset the ignition timing until I am sick of paying for it. I have changed to richer carb jets, replaced the fan clutch, checked my 7-bladed fan, changed to a new DeWitt's aluminum radiator ($900), changed thermostats, checked for collapsed hoses, IR'd the various spots, etc. to no avail. I have done everything that this forum has suggested except change out the water pump or dismantle the engine.

I want to keep my car "NCRS Top Flight" original to do well in upcoming regional and national flight judging. So, I am reluctant to do anything at this time that would make my car appear less correct. So, electric fans and a larger radiator is not in the picture.

But, I noticed in the Long Island catalog that for a 1966 small block with A/C, there are upper and lower radiator "seals" listed (sec. #26). Other than these seals being incorrect for a 1965 (according to the catalog), would the installation of these '66 upper and lower radiator seals help my car run cooler with the A/C on, in hot weather? What say you experts out there?

Clark-----

Installation of the seals should make a significant difference. If it were me, I'd install seals around the complete perimeter, not just upper and lower. Ideally, you want to have all the "gaps" between the radiator and support sealed as well as all the "gaps" between the shroud and the radiator.

If the above doesn't completely solve the problem, I'd go with a higher performance fan clutch, albeit incorrect.

[Peter L.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark - I'm thinking that the engineers added the seals for a reason and more than likely it was to reduce over heating on C60 Corvettes when the AC was on. The addition of the upper radiator seal is a simple operation and could be easily removed if needed since it's attached with clips. The lower seal appears to be glued in but it might not be that visible.

Anyway, it seems like a relatively inexpensive experiment to run and if it works, it might be the answer for other pre-1966 C60 Corvette owners who have experienced over heating with the AC on. If you do it, hopefully it will be successful and if it is, be sure to post something on the DB.

Pete

[Patrick H.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark,

Despite the old wives' tales you are hearing, a couple of questions:

1. Is your car actually overheating? You don't say that it is; I assume you at least think it is.

2. If overheating, how do you determine this? Gauge? IR readings, when and where? Coolant spilling over the ground?

We need more information.

Also, what radiator cap are you using?

Patrick

[Kenneth S.]

Re: I Dare Not Use the C-60 When it is Hot Outside


Ken

[Stuart F.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Now you know why I chose to buy a Convertible in 63. I had test driven two coupes in El Paso in the spring of 63, during the usual desert heat, and determined the coupe was not for me. I don't regret that decision even today with the obvious value advantage of a 63 SWC over my rag top. I know, the 63 SWC is the worst example due to it not even having an exhaust fan, but with a performance car like this, it is better to do w/o A/C and "drop the top".

Stu Fox

[Mike G.]

I picked up 10 degrees improvement by

installing the top air dam flap (6 clips)

reclocking the clutch spring 180* ccw to open the fluid valve wider and increase viscous coupling

and punching louvers in the large splash shields. About 20 in each, punched down and facing aft to create a low pressure gradient and draw the hot air out of the engine compartment.

The car is a 300hp 1965 and it still gets hot (225) at idle when the ambient temp is 95+* (a normal day here in So. AZ). But I'm not fully broken in yet, so there may be some further cooling performance ahead.

[Jim T.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark I am not familiar with your 1965's Holley although I have used Holleys since 1974. Does your Holley have a tube coming from the front metering block? If it does, this is a ported vacuum tube.
Ported vacuum if used as a source of engine vacuum for the vacuum advance unit on the distributor will contribute higher engine temps when driving in traffic and sitting at traffic lights.
What is your timing set at BTDC?
The centrifical advance could benefit from a cleaning and very light lubrication. My 1964 Corvette was only 5 years old when the centrifical advance would advance and not retard when the engine got to operating temperature because it needed a good cleaning.
A working vacuum advance unit connected to full time vacuum source will also contribute to lower engine temperatures.

[Duke W.]

Re: I Dare Not Use the C-60 When it is Hot Outside

I have had experts set and reset the ignition timing until I am sick of paying for it. I have changed to richer carb jets, replaced the fan clutch,

Spend fifty bucks and buy a dial back timing light. Get a vacuum gage while you're at it.

What's the initial timing?

What's the total idle timing?

What's the total WOT timing?

Do the centrifugal and vacuum advance meet OE spec?

What's the idle speed/manifold vacuum? Compressor off? Compressor on?

No one can diagnose a problem without some basic test data!

Current replacement fan clutches are designed for 195 ...stats and don't tighten until a higher radiator exit air temperature compared to the OE clutches that were set up for 170/180 ...stats. So...?

Duke

[Clark K.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark,

Despite the old wives' tales you are hearing, a couple of questions:

1. Is your car actually overheating? You don't say that it is; I assume you at least think it is.

2. If overheating, how do you determine this? Gauge? IR readings, when and where? Coolant spilling over the ground?

We need more information.

Also, what radiator cap are you using?

Patrick

Patrick, the car is NOT overheating, just giving the appearance that it WILL at some point if things continue. I will never allow the temperature gauge to peg all the way over to the right side. So, I have NOT experienced a boil-over for the same reason. I shut off the A/C long before that can happen.

I had an "expert" IR gun the various places and he determined that the car was running hotter than it should with a stock 180 degree thermostat. He also determined that the gauge was accurate. His report caused me to buy a new correct DeWitt radiator.

I am using a reproduction RC-26 cap (15psi) for an A/C car. The car is a RARE L76 (327/365) with C-60 (factory A/C). -Clark

[Clark K.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Ken

Ken, my reasoning tells me that if the condenser was clogged/partially clogged, the car would run hotter than normal even if the A/C was turned off. This is not the case.

Now, the belt issue you mention is something that I haven't seen before. I am running repro Quanta belts since my car is a Top Flight car. -Clark

[Clark K.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark I am not familiar with your 1965's Holley although I have used Holleys since 1974. Does your Holley have a tube coming from the front metering block? If it does, this is a ported vacuum tube.
Ported vacuum if used as a source of engine vacuum for the vacuum advance unit on the distributor will contribute higher engine temps when driving in traffic and sitting at traffic lights.
What is your timing set at BTDC?
The centrifical advance could benefit from a cleaning and very light lubrication. My 1964 Corvette was only 5 years old when the centrifical advance would advance and not retard when the engine got to operating temperature because it needed a good cleaning.
A working vacuum advance unit connected to full time vacuum source will also contribute to lower engine temperatures.

Jim, I had my entire distributor/ignition system overhauled last winter. The vacuum advance is dead on stock specs.
-Clark

[Clark K.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Spend fifty bucks and buy a dial back timing light. Get a vacuum gage while you're at it.

What's the initial timing?

What's the total idle timing?

What's the total WOT timing?

Do the centrifugal and vacuum advance meet OE spec?

What's the idle speed/manifold vacuum? Compressor off? Compressor on?

No one can diagnose a problem without some basic test data!

Current replacement fan clutches are designed for 195 ...stats and don't tighten until a higher radiator exit air temperature compared to the OE clutches that were set up for 170/180 ...stats. So...?

Duke

Thanks for weighing in, Duke. I did not intend to aggravate you by failing to give adequate data. All that you noted has already been done by two different shops. I do not remember the specs but nothing was found wrong except a loose plug wire and a pinched coil wire, which were immediately and permanently remedied.

What I keep hearing when I discuss this off this forum with knowledeable people is that "all L76's with C-60 run too hot and that is why they are so rare". If this is true, then I will accept this until the car takes National Top Flight next summer and then it will be modified/remedied with incorrect for the model year seals, radiator, electric fans, etc. -Clark

[Jean C.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark,
I would run the car with A/C to see if the temp gauge actually gets into the hot zone and it either does or does not puke coolant.

It doesn't take an "expert" to use and IR gun. Buy one and check the temp when running/driving the car with the A/C on to see what the temp actually rises to. If it is determined to be getting overly hot, turn off the A/C and drive the car to cool it down before turning off the engine.

See you in Killeen.
Best regards,

[David B.]

Re: I Dare Not Use the C-60 When it is Hot Outside

Clark,
Is the engine block over bored?
If so How much.

Dave