1968 Cooling Issues

[Paul P.]

Re: 1968 Cooling Issues

All:

Update on the cooling issues situation. I've purchased an IR temperature gauge (thanks for the suggestion Patrick) and have found the following:

Radiator center 200 degrees fahrenheit
Top of radiator 186 degrees fahrenheit
Thermostat housing 190 degrees fahrenheit
Supply Tank bottom 299 degrees fahrenheit
Supply Tank top 149 degrees fahrenheit

This was after my morning commute, the car was idling. Coolant is still spewing out from the supply tank after I stopped. I also smell occasional whiffs of coolant while driving.

I don't think I have an overheating issue. What has occurred to me, after seeing the almost 300 degrees fahrenheit at the supply tank bottom, is that the headers are maybe overheating the tank? I do not have the stock exhaust manifold; a set of performance headers was installed by the previous owner.

I do not see any sign of a heat shield. Was there one on the 1968 Corvettes?

I now see two possible solutions. I could A) install a heat shield or B) install stock exhaust manifolds.

Comments?

[Joe L.]

Re: 1968 Cooling Issues

All:

Update on the cooling issues situation. I've purchased an IR temperature gauge (thanks for the suggestion Patrick) and have found the following:

Radiator center 200 degrees fahrenheit
Top of radiator 186 degrees fahrenheit
Thermostat housing 190 degrees fahrenheit
Supply Tank bottom 299 degrees fahrenheit
Supply Tank top 149 degrees fahrenheit

This was after my morning commute, the car was idling. Coolant is still spewing out from the supply tank after I stopped. I also smell occasional whiffs of coolant while driving.

I don't think I have an overheating issue. What has occurred to me, after seeing the almost 300 degrees fahrenheit at the supply tank bottom, is that the headers are maybe overheating the tank? I do not have the stock exhaust manifold; a set of performance headers was installed by the previous owner.

I do not see any sign of a heat shield. Was there one on the 1968 Corvettes?

I now see two possible solutions. I could A) install a heat shield or B) install stock exhaust manifolds.

Comments?

Paul------


You've got headers? I'd get rid of those so fast it would make your head swim.

[Paul P.]

Re: 1968 Cooling Issues

Joe:

Like I said, they were put there by a previous owner. I didn't like them when I first saw them either.

Do you think they have something to do with my problem?

~paul

Paul------


You've got headers? I'd get rid of those so fast it would make your head swim.

[Joe L.]

Re: 1968 Cooling Issues

Joe:

Like I said, they were put there by a previous owner. I didn't like them when I first saw them either.

Do you think they have something to do with my problem?

~paul

paul------


I don't know if it's the entire problem. However, headers usually increase underhood temperatures via increased heat radiation from the relatively thin wall headers AND the fact that they were not "engineered into the car". I would NEVER, EVER, EVER, EVER use aftermarket headers on a street-driven car. NEVER, EVER. PERIOD.

[Dick W.]

Re: 1968 Cooling Issues

Joe:

Like I said, they were put there by a previous owner. I didn't like them when I first saw them either.

Do you think they have something to do with my problem?

~paul

Had several Vettes with headers and never had that problem.

[Paul P.]

Re: 1968 Cooling Issues

Problem solved.

The solution was to replace a leaky heater core. I knew the heater core was leaking because when I turned on the COLD / HOT console control to "HOT" there was a mist of coolant emanating from the dash. I just set it to back to "COLD".

Why the leaky heater core was the problem is a mystery to me. I figured that with the setting on "COLD" the heater core was not in the system.

The cooling system now runs as expected. I drive the '68 from Los Angeles to Las Vegas for the NCRS convention - had a great time - and not a drop of coolant was lost. This was during a significant heat wave, over 110 degrees!

Apparently there needs to be a certain pressure in the system that the leaky heater core violated? The supply tank still measures ~ 300 degrees but the coolant does not spew out. I assume it goes back into the radiator.

Any ideas?

And thanks to those who responded with help, suggestions, etc. It was appreciated.

~paul

I would like to get a handle on cooling issues with my 1968 convertible.

During normal operation, the temp gauge is typically just to the right of the mark between the 100 and 250 marks. If it is a cool day, it may be just to the left of the mark. Under the very worst conditions, (extremely hot Los Angeles day, stop and go traffic, etc.) it will approach, but stay to the left of the 250 mark. Admittedly I have not checked the thermostat status.

When I stop and park it on a hot day, the overflow tank spews out some coolant.

The engine is not original, a 350, and I'm told an "010" block which is (again I'm told) a replacement block popular in the '80s. Carburetion (Quadrajet) and heads are from other years so it is a bit of a Frankenstein. It was recently tuned by a competent professional, so I assume timing and air/fuel ratio is OK.

I have little on the previous history of the car. The build date is July 26, 1968.

Please see the attached photos. There are cutouts in the body below the bumpers, which again I've been told, are part of the updates from GM to deal with cooling issues. True?

It looks to me like the fan blades are outside of the fan shroud which might limit their effectiveness? I recall a restoration TV program where they extended the fan shroud to cover the fan blades to deal with overheating on a 1968, although the car was a big block.

The cap on the expansion tank was replaced with a better quality unit rated at 15#, no difference.

Another issue: How do I add coolant? Again, there is much on this car that is not correct. The only opening is the expansion tank. But I don't see how that would fill the radiator engine. Should I expect the engine to fill itself from the tank somehow? Or should I force coolant in via disconnecting the upper radiator hose? If I squeeze the upper radiator hose (which feels empty) I can somehow suck some coolant in from the expansion tank. I am using a 50/50 Prestone / water mix.

Is water wetter recommended?

I'll be taking it to the NCRS convention in Las Vegas and would like to have the coolant spewing under control.

Any recommendations?


~paul

[Terry M.]

Re: 1968 Cooling Issues

Problem solved.

The solution was to replace a leaky heater core. I knew the heater core was leaking because when I turned on the COLD / HOT console control to "HOT" there was a mist of coolant emanating from the dash. I just set it to back to "COLD".

Why the leaky heater core was the problem is a mystery to me. I figured that with the setting on "COLD" the heater core was not in the system.

The cooling system now runs as expected. I drive the '68 from Los Angeles to Las Vegas for the NCRS convention - had a great time - and not a drop of coolant was lost. This was during a significant heat wave, over 110 degrees!

Apparently there needs to be a certain pressure in the system that the leaky heater core violated? The supply tank still measures ~ 300 degrees but the coolant does not spew out. I assume it goes back into the radiator.

Any ideas?

And thanks to those who responded with help, suggestions, etc. It was appreciated.

~paul

Paul
Pressure in the cooling system is essential to maintaining proper function. With a 14 to 15 pound pressure cap (typical for our Corvettes) coolant boiling point is raised about 40 to 45 degrees F. So at no pressure the coolant will boil at 212 degrees. With proper pressure that boiling point is raised to 252 to 257 degrees. With a coolant leak in the heater core, or anywhere else in the system, you will have no pressure and the coolant will boil at 212 degrees.

Turning the temperature control to cool only directs incoming air around the heater core. The heater core is still in the system.

I am glad you solved your problem and enjoyed the National.