Radiator-Expansion Tank or Overflow?

Which is better (for cooling), the expansion tank used on early C3's or the overflow reservoir used on 73-up?

Want the honest truth?? I put one of them kidney shaped white plastic later shark overflow tanks in my '72 here and have not noticed one damn thing differant for having it....nuttin....time money waster far as I can tell....

:bonkers:

BBShark said:

Which is better (for cooling), the expansion tank used on early C3's or the overflow reservoir used on 73-up?

Click to expand...

Actually, expansion tank. The new cooling systems have gone back to this to insure the rad is always completely filled.My 2003 truck has one.
My old time radiator guy hated the overflows. He said they caused problems not allowing room for expansion.

The expansion is used when the radiator is not the highest part of the cooling system. The tank is then mounted somewhere where it's aat the highest point.

I don't see any other very apparent differences and wouldn't know why one would be better than the other.

I thought they were all the same, what's the diff???

:bonkers:

An expansion tank is pressurized, the system's pressure cap is on the tank. An overflow tank is not pressurized, it's open to the atmosphere. Whenever system pressure is exceeded the cap opens and excess coolant pukes in the overflow tank

You can simply use an expansion tank on a radiator with a cap. Just make sure the cap on the rad is rated higher than on the tank.

Twin_Turbo said:

I don't see any other very apparent differences and wouldn't know why one would be better than the other.

Click to expand...

Here is the explanation given to me by a 35 year radiator veteran. Follow the logic.
We all know when you fill a radiator full, when the pressure excedes 16 lbs, the cap allows coolant into the tank. When it cools, it syphons/vacuums the coolant back in, keeping the system full.
Before/way back when before recovery, you were supposed to fill to the bottom of the neck, leaving air for expansion.
He always told me to leave the same air space with the new recovery systems. He said when they introduced them, people filled them all the way.Now, instead of compressable air at 16lbs, you get 16lbs hydrallic pressure first, before the cap vents to the tank.
He also stated before they came around, the least trouble they had was with the old vette expansion tank system, since it kept the core full, yet left compressable air space in the tank.
The logic may be flawed, but were talking about a guy who rodded/recored radiators for 35 years, maybe twice a day, 300 days a year. That's alot of hands on..
I will also be posting a new thread about what really happens to corrosion in the old brass radiators as explaned to me by the oldtymers. Never would have thought about it as explained to me.

Twin_Turbo said:

An expansion tank is pressurized, the system's pressure cap is on the tank. An overflow tank is not pressurized, it's open to the atmosphere. Whenever system pressure is exceeded the cap opens and excess coolant pukes in the overflow tank

Click to expand...

To clarify, an overflow tank/puke can as we called it, was just a catch can for overflow.
A "recovery" tank has a syphon hose that allows coolant to vacuum back in during cool down.
An expansion tank is a remotely mounted tank at the high point of the system, as Marck has stated. It has the cap.
This is the way GM is doing it once again.

They are doing it with the pressurized expansion tanks because the top of the rad is not the highest point in these cars anymore. There's no other way to do it and get all the air out

I am asking this for a couple of reasons. First I am converting my 68 to a 69 radiator and support. The 73-up radiator appears to be the same dimensions as the 69 but with an overflow reservoir (73-up) instead of the expansion tank (69-72). Second, the C4 was introduced with a overflow reservoir (I think) and then changed to an expansion tank later.

Intuitively it seems like the C3 expansion system is better but is it much better or just marginally better?

BBShark said:

I am asking this for a couple of reasons. First I am converting my 68 to a 69 radiator and support. The 73-up radiator appears to be the same dimensions as the 69 but with an overflow reservoir (73-up) instead of the expansion tank (69-72). Second, the C4 was introduced with a overflow reservoir (I think) and then changed to an expansion tank later.

Intuitively it seems like the C3 expansion system is better but is it much better or just marginally better?

Click to expand...

Bob, like I stated above, I can't tell one damn whit damn differance wether the tank is there or not...and come think of it, I have a 'thing' against STANT thermostats, and witched to Murray...which is much better more reliable operation Stants had a habit of not opening until the engine was 220f, when the stat was supposed to be 180....

NOW, even with that white plastic tank in circuit, I notice the rad still runs with the level some distance down from the top, but I see no leakage anywhere....

no overheating either...runs entirely normal in Florida heat which has been 95+ for a while now, and supposed to be over 100 today....

:crap:

My 68 has the aluminum expansion tank that looks like a mini-beer keg. I bought a Be-Cool aluminum radiator and it came with a Be-Cool radiator cap with the spring loaded valve mechanism built into the cap. To keep the functionality of my stock aluminum expansion tank, I neutered my Be-Cool cap. I took a dremil and cut the spring off and also cut off the little valve a the end of the spring--the little disk with the rubber seal. Now, when I put my Be-Cool cap on, it acts as a pure cap and allows coolant to flow into the expansion tank. (Remember the early C3 aluminum radiators did not have radiator caps on them.) The expansion tank of course has a proper "radiator" cap on it. Works fine.

FYI: the aluminum expansion tanks are now made by DeWitt using the original factory tooling (I think). Also, I have pure ethylene glycol (no water) in my radiator with the result that my coolant system will not pressurize. On some of my first check out rides, I didn't have any hose clamps on the hoses. (I've since added them.) My engine, a ZZ4, runs very cool.

BBShark said:

I am asking this for a couple of reasons. First I am converting my 68 to a 69 radiator and support. The 73-up radiator appears to be the same dimensions as the 69 but with an overflow reservoir (73-up) instead of the expansion tank (69-72). Second, the C4 was introduced with a overflow reservoir (I think) and then changed to an expansion tank later.

Intuitively it seems like the C3 expansion system is better but is it much better or just marginally better?

Click to expand...

The expansion tank is the way a pipefitter would plumb a cooling tower, hydronic heating loop, or any other closed system. It IS better. However, if space proves to be a hardship, I don't know as i would stay awake nights.:wink:

On my 69, the hose from the radiator went into the top end of my overflow or expansion tank--what ever you call it--and it could not suck coolant back to the radiator, only air. You have to make sure that the hose end is down into the coolant in the bottom part of your tank. I un-soldered the copper tube in the end of the tank and re-soldered a 90 deg bend piece of copper tubing that extended close to the bottom of the tank. Over the next 4 or 5 start/stop runs, I put a additional 3 qts of coolant into the system.

BBShark said:

I am asking this for a couple of reasons. First I am converting my 68 to a 69 radiator and support. The 73-up radiator appears to be the same dimensions as the 69 but with an overflow reservoir (73-up) instead of the expansion tank (69-72). Second, the C4 was introduced with a overflow reservoir (I think) and then changed to an expansion tank later.

Intuitively it seems like the C3 expansion system is better but is it much better or just marginally better?

Click to expand...

The C3 rads that used an external expansion tank had the aluminum Harrison Plate type rads. This type of rad and not the expanson setup was what was a better design and cooled much better per sq in than the copper rads. It would be very difficult to put expansion end tanks on this type of rad. To expell the air out of the rad and to the expansion tank, the small fitting was on the top of the top plate. The solid coolant return to the rad, came out of the bottom of the remote expansion tank via the heater suction line.
If you think air may be an issue then just add a bleed screw to the tstat housing. Many cars have them including BMW, Mercedes and and even the old Panteras had a bleed screw on the top of the radiators.

The biggest reason for GM to not use this remote exp tank setup was that size was no longer a constraint in a C3. I believe that a 75 C3 has the largest rad size and if using an aluminum 75 rad, that would probably give the greatest cooling capacity.