1968 Cooling Issues

[Paul P.]

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

[Patrick H.]

Re: 1968 Cooling Issues

1. Fan should be half in, half out of the shroud. Yours is almost completely out. It might be a water pump issue, pulley issue, fan clutch issue, etc that causes the incorrect spacing.

2. Add 50/50 coolant/water in the expansion tank.

3. Do not add Water Wetter.

4. If you overfill the system, it will puke coolant. This does not mean it overheated. The expansion tank should be "about" half full if done correctly, but the system will often seek its own level, ie. puke out any extra. I learned this the hard way years ago. Ignore it, and it seeks its own level and stops. Keep adding more, and it will keep puking coolant.

5. The thermostat will not affect how hot it gets.

6. An inexpensive IR temp gun can help figure out the actual temperature.

7. Timing issues can cause overheating, despite any recent tune-up.

[Joe L.]

Re: 1968 Cooling Issues

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

Paul------


This car has a copper/brass replacement for the original aluminum radiator. These do not cool as well as the original aluminum. In fact, I've always considered these replacements marginal, at best, and deficient when conditions are tough.

In all Corvette installations with a remote supply tank, the radiator is filled through the supply tank. I'm talking about a supply tank now, NOT a coolant recovery reservoir. No Corvette had a coolant recovery reservoir prior to 1973

[Duke W.]

Re: 1968 Cooling Issues

Likely it has ported vacuum advance. Check that, and if it is ported type, convert to full time. Check manifold vacuum at idle and if necessary replace the VAC with one that passes the Two-Inch Rule.

This change will significantly reduce heat rejected to the cooling system at idle and low load, which will lower stop and go driving temperature. With ported vacuum advance exhaust manifold temperature is around 900, but should be no more than 500F with a functionally corrrect full time VAC.

Duke

[Paul P.]

Re: 1968 Cooling Issues

Thank you for the response Patrick. I do put 50 / 50 in the expansion tank. I've also only filled it to the indicated line, which is about half full. I was aware of the practice. I'll take it on faith that the system will find it's own level. But I get nervous when I squeeze the upper radiator hose and it seems empty.

The IR Temp gun is a good idea, hadn't thought of that. $22 on Amazon, done.

I will check the timing.

Thank you again.

~paul

[Paul P.]

Re: 1968 Cooling Issues

Joe:

That's interesting about the copper / brass radiator and the originals being aluminum. Now thinking seriously about a replacement from one of the reputable Corvette vendors. I noticed that they include a conventional fill port.

What is the difference between a remote supply tank and coolant recovery reservoir? I referred to what I have as an expansion tank as that was the term used in the catalogs.

Thank you for responding.

~paul

[Paul P.]

Re: 1968 Cooling Issues

Duke:

Not sure what converting ported vacuum advance to full time is or how to do it. Also not familiar with the two inch rule, will have to do some research.

~paul

Likely it has ported vacuum advance. Check that, and if it is ported type, convert to full time. Check manifold vacuum at idle and if necessary replace the VAC with one that passes the Two-Inch Rule.

This change will significantly reduce heat rejected to the cooling system at idle and low load, which will lower stop and go driving temperature. With ported vacuum advance exhaust manifold temperature is around 900, but should be no more than 500F with a functionally corrrect full time VAC.

Duke

[Joe L.]

Re: 1968 Cooling Issues

Joe:

That's interesting about the copper / brass radiator and the originals being aluminum. Now thinking seriously about a replacement from one of the reputable Corvette vendors. I noticed that they include a conventional fill port.

What is the difference between a remote supply tank and coolant recovery reservoir? I referred to what I have as an expansion tank as that was the term used in the catalogs.

Thank you for responding.

~paul

paul-----


The original aluminum radiator for your application used a remote supply tank and had no integral filler. Reproductions of these are available as manufactured by DeWitts. These are expensive but I highly recommend them. Using any other aftermarket radiator will require other modifications.

The actual term used by GM for the tank used for your application is SUPPLY TANK. "Expansion tank" is a term used in the vernacular but it's not the technically correct term. In the case of the original aluminum radiator used for your application, that radiator had NO integral tanks; it was essentially just a core. So, the external supply tank served as that radiator's only tank. Generally, supply tanks are not used with radiators with integral tanks and such radiators generally have an integral filler on one of the tanks. There was one exception, though. That exception was 1969-72 Corvettes with big block. Those application used a large copper/brass radiator with integral tanks, no integral filler and an external supply tank.

A coolant recovery reservoir is used on 1973 and later Corvettes. This is a system simply designed to capture coolant lost through pressure cap relieving and return it to the cooling system. On most such applications the cooling system can be "topped off" by adding coolant to the reservoir, though. More specifically, a SUPPLY TANK is part of the pressurized cooling system (just as are integral tanks used with most radiators). A COOLANT RECOVERY RESERVOIR is not part of the pressurized cooling system.

[Duke W.]

Re: 1968 Cooling Issues

Duke:

Not sure what converting ported vacuum advance to full time is or how to do it. Also not familiar with the two inch rule, will have to do some research.

~paul

Start by searching the Web for my tuning seminar - duke Williams san diego corvette - download the pdf and study it. Pay particular attention to the slide on emission controlled engines.

Duke

[Dick W.]

Re: 1968 Cooling Issues

Joe:

That's interesting about the copper / brass radiator and the originals being aluminum. Now thinking seriously about a replacement from one of the reputable Corvette vendors. I noticed that they include a conventional fill port.

What is the difference between a remote supply tank and coolant recovery reservoir? I referred to what I have as an expansion tank as that was the term used in the catalogs.

Thank you for responding.

~paul

Correct replacement radiator is available from DeWitts their #1139063M for $549.99

[Brad Hillhouse (37766)]

Re: 1968 Cooling Issues

Correct replacement radiator is available from DeWitts their #1139063M for $549.99

That radiator will fit, but it is definitely not "correct". The correct one is $999.99 and is in the Dewitts restoration radiator line, not the direct fit line:

https://www.dewitts.com/collections/corvette-aluminum-radiators/products/1965-1972-restoration-radiator

Brad Hillhouse
37766

[Paul P.]

Re: 1968 Cooling Issues

Thank you Joe for the explanation. Very clear and I now have a better understanding of the situation.


~paul

[Paul P.]

Re: 1968 Cooling Issues

Thank you Brad and Dick for the DeWitts info. My 1968 is a driver and not original, so I may go with the lower cost version.

Thanks to all who took the time to offer advice, etc, it is highly appreciated.


~paul

[Joe L.]

Re: 1968 Cooling Issues

Thank you Brad and Dick for the DeWitts info. My 1968 is a driver and not original, so I may go with the lower cost version.

Thanks to all who took the time to offer advice, etc, it is highly appreciated.


~paul

paul------


The DeWitts "Direct Fit" that Dick mentioned above will work for your application without modification. While not NCRS-correct, it will provide cooling performance far better than the unit you have now----probably roughly equivalent to the original type, aluminum "stacked plate" design.

[Dick W.]

Re: 1968 Cooling Issues

Thank you Brad and Dick for the DeWitts info. My 1968 is a driver and not original, so I may go with the lower cost version.

Thanks to all who took the time to offer advice, etc, it is highly appreciated.


~paul

You could call Tom DeWitt and ask him the difference in the heat rejection between the two.