C3: Surge tanks vs Overflow Reserviors re JL

[Tom R.]

Perusing the archives on the topic of surge tanks, I came across a thread or two that intimated a difference between the surge tanks of 1968-72 (and previously) and the post-73 off-white molded translucent plastic tanks.

The indication was that the aluminum/brass tanks are surge/coolant tanks and the translucent are overflow/reservior tanks. From 68-72, AIMs referred to them as radiator supply tanks and we see reference evolve to radiator overflow sytem and finally coolant recovery system. The tanks in 73 were titled "tanks" and later "overflow tanks."

What's the difference in functionality? It appears its the same.

[Joe L.]

Re: C3: Surge tanks vs Overflow Reserviors re JL

Tom-----

There's a big difference. Radiator supply tanks, as used for many 1962-72 Corvettes, were an integral and critical part of the PRESSURIZED cooling system. For one thing, the vast majority of the cars that used them also used the "stacked-plate" design aluminum radiators. These radiators have no integral tanks (i.e. they are really just a "core") and they have no filler provisions. The external supply tank serves the same purpose as the integral tanks on conventional radiators. The only exception to this were 1969-72 big block radiators. These copper/brass radiators did have integral tanks, but they had no filler provisions. The external supply tank provided extra tank capacity AND provided the system filler.

On all systems which used the external supply tank, pressure relief and overflow provisions were at the tank. Overflow for all of these systems went to atmosphere.

Beginning in 1973, ALL Corvettes used radiators with integral tanks and filler neck. However, instead of overflow going to atmosphere, it was directed to an "overflow tank" or coolant recovery tank. This tank captured the overflow and directed it back to the cooling system. This function is completely different than the function of the 62-72 coolant supply tanks. The coolant recovery tanks are NOT part of the PRESSURIZED cooling system.

[Tom D.]

1968 vs. 1969 Big Block Radiators Diff.

Joe: I conclude from your post that, unlike 69-72, the 1968 and older big block radiators do have a filler opening and a removable "pressurized" cap.

What differences, if any, between 1965 and 1968 (big block radiators)?.

Thanks
Tom D.

[Tom R.]

[Joe L.]

Re: 1968 vs. 1969 Big Block Radiators Diff.

Tom-----

Yes, 1966-68 Corvette big block radiators were the same and use a integral filler/pressure cap on the right side tank. No external supply tank is used for these applications. Although the 66-68 big block radiators (except L-88) were the same, in PRODUCTION different radiators were used for manual transmission cars as opposed to auto trans cars. The auto trans car radiator, GM #3008566, had an integral trans oil cooler and the manual trans radiator, GM #3008567, did not. The non-oil cooler radiator was discontinued from SERVICE years ago and replaced by the oil cooler type which SERVICED all 66-68 big block applications until it was discontinued and replaced by a non-Harrison, aftermarket-type unit.

All 1965 Corvettes with big block (and, 67-69 Corvettes with L-88), use a HD aluminum radiator which did use an external supply tank. The radiator used for most 1965 L-78s was GM #3007436 and this same radiator was also used for all L-88s (except those 69 L-88s originally equipped with THM-400 which used copper/brass radiator GM #3019190).

[Joe L.]

Re: C3: Surge tanks vs Overflow Reserviors re JL

Tom------

1) Yes, all 1973-82 Corvette radiators are cross-flow and use integral TANKS on both sides of the radiator;

2) Almost, but not exactly. All pre-73 systems with aluminum radiator use radiators with NO integral tanks, at all. The external supply tank is the only tank in the system and the tank includes the filler and pressure cap. 1969-72 Corvettes with big block and copper brass radiators do have integral tanks on each side of the radiator, but no integral filler. These systems use an external supply tank which includes provisions for filler and pressure cap. During the 53-82 period, the 69-72 big block radiators are the only ones that use an external supply tank with a radiator that has integral tanks;

3) Correct, all pre-73 Corvette cooling systems vent to atmosphere or "ground". There are no coolant recovery systems originally installed on these cars. It would be very possible to RETROFIT a coolant recovery system to the cars if so desired, though;

4) Correct

5) Correct, Un pre-73 systems the entire cooling system is pressurized INCLUDING the radiator and external supply tank where they are used. For 1973 and later the coolant recovery tank is not part of the pressurized system;

6) 1984-89 Corvettes use a system which includes an aluminum radiator with integral plastic tanks and a filler neck/pressure cap on the right side tank. There is a coolant recovery system which is similar to the 73-82 Corvette systems. The radiator is part of the pressurized cooling system. The coolant recovery tank is not part of the pressurized system;

1990-96 C4s use an aluminum radiator with plastic side tanks with no filler provisions. The system also includes an external surge tank with filler/pressure relief cap. A coolant recovery tank operates to recover and return coolant to the surge tank. The radiator and surge tank are part of the pressurized cooling system; the coolant recovery tank is not part of the pressurized cooling system.

[Tom R.]