L-71 Thermostat

[Michael W.]

Re: L-71 Thermostat

My car does not run an overflow tank, I assume yours doesn't either.

No C2/C3 Corvette prior to '73MY has an overflow tank (an unpressurised vessel that collects and returns coolant). All C2/C3 Corvettes prior to '73MY have internal expansion tanks only, either integral to the radiator or as an external tank which forms part of the pressurized coolant system.

I have learned that the Corvette was one of the last GM vehicles to incorporate an overflow tank, seems strange as it was one of the best things to come along.

[Joe R.]

Re: L-71 Thermostat

No C2/C3 Corvette prior to '73MY has an overflow tank (an unpressurised vessel that collects and returns coolant). All C2/C3 Corvettes prior to '73MY have internal expansion tanks only, either integral to the radiator or as an external tank which forms part of the pressurized coolant system.

I have learned that the Corvette was one of the last GM vehicles to incorporate an overflow tank, seems strange as it was one of the best things to come along.

Michael,

I assume your comments apply only to big blocks, correct? I'm pretty sure the L78 ('65 396) does have the external overflow tank. It may be the only SHP BB that does. I thought the L36, etc. (in other words, non-SHP BB's) had the external overflow tank, too. But I could certainly be wrong on that.

Joe

[Duke W.]

Re: L-71 Thermostat

All engines with aluminum radiators (which includes L-78) have external pressurized expansion tanks and the owners'/service manuals say the tank should be half full when the coolant is COLD.

Brass radiators (all big blocks except L-78, L-88, and ZL-1) have an integral expansion tank, and the owners/service manuals should say how much free space there should be between the top of the liquid and radiator cap - either hot or cold, or both. It's probably in the range of 1-2".

You could also install an external non-pressurized coolant recovery tank (which became standard on Corvettes with conventional brass radiators by the mid seventies) and run the coolant all the way to the top of the radiator.

Duke

[Michael W.]

Re: L-71 Thermostat

Michael,

I assume your comments apply only to big blocks, correct? I'm pretty sure the L78 ('65 396) does have the external overflow tank. It may be the only SHP BB that does. I thought the L36, etc. (in other words, non-SHP BB's) had the external overflow tank, too. But I could certainly be wrong on that.

Joe

That's an expansion tank, not an overflow tank. Different animal. The aluminum expansion tanks were part of the pressurized system and exist with radiators that have no internal expansion tanks. There's lots of owner inspired hybrid systems out there, no Corvette ever came with two radiator caps.

[Joe L.]

Re: L-71 Thermostat

No, I have no marks on the outside except the "Harrison". No, I have no recovery tank, as no BBs did I think. Although I have thought about getting one when it keep puking out coolant. How far below the top of the radiator cap neck is your mark? I have tried up to 5 inches below that (with several rows of tubes exposed and dry) as fill level and it still pukes. Maybe my RC-15 cap is weak. It is new, but I guess they can be bad from new.

Michael------

For 1967, L-88 used an external supply tank, but no other big blocks did. 1968 was the same. No 1966 Corvette big block used an external supply tank. However, for 1965 ALL L-78 did use an external supply tank.

For 1969-72 ALL big blocks used an external supply tank regardless of whether they had a copper/brass or aluminum radiator.

No C3 Corvette after 1972 used an external supply tank but ALL had coolant recovery tanks.

[Joe R.]

Re: L-71 Thermostat

How far below the top of the radiator cap neck is your mark?

Michael,

The mark on mine is 3 3/4 " below the cap mating surface. If you look closely at the picture you can see the words "FILL COLD" plus an arrow. The 3.75 " dimension I gave is to the top of the arrowhead. Now, I should mention that I don't know if my radiator is original or not. I'm pretty sure it has some Harrison markings on it, but that's about all I know about it.

Joe

[Michael J.]

Re: L-71 Thermostat

Michael,

The mark on mine is 3 3/4 " below the cap mating surface. If you look closely at the picture you can see the words "FILL COLD" plus an arrow. The 3.75 " dimension I gave is to the top of the arrowhead. Now, I should mention that I don't know if my radiator is original or not. I'm pretty sure it has some Harrison markings on it, but that's about all I know about it.

Joe

That part of my radiator is behind the shroud frame and not visible. I have tried a 4" below the neck fill without any luck. I think I will get the new recommended thermostat, and have my RC-15 pressure tested and if it fails replace it, and see if that helps. Thanks.