Expansion Tank Installation Issue

[Jasper]

I have a restored 1970 LT-1 convertible with the factory 350 cubic inch 370 horsepower motor and four speed transmission but no power steering or brakes. (I love this car and the females of the species seem to do so, as well.) I decided to add an expansion tank to the cooling system out of a desire to keep the radiator core covered with coolant at all times. I bought a kit from an aftermarket supplier that was represented as having all the necessary parts for the installation: tank, hoses, bracket, clamps, et cetera. The kit included a "T" shaped adapter that I could not understand that I needed. I was surprised that the set up is not a non-pressurized overflow tank in the more modern style; instead, it is a fully pressurized element in the cooling system. The tank has two nipples on its bottom, a nipple near the top, and an overflow nipple on its neck just under the cap. I cut one of the heater hoses and placed the cut ends onto the two lower nipples of the tank. I removed the overflow hose from the radiator and placed it on the overflow nipple of the new tank. I then completed the installation by connecting the overflow nipple of the radiator to the input/output nipple near the top of the expansion tank.
I am sure that I did something wrong because when I started the engine from cold, coolant pumped out from under the radiator cap. (Both the radiator and expansion tank have caps rated at 15 pounds.) It seems that coolant is pressurized in the expansion tank and forced back toward the radiator where it escapes under its cap. Something is clearly amiss here.
What did I do wrong? Should the "T" shaped adapter be brought into play someway? If so, how?

[c4c5specialist]

HI there,

I am having trouble picturing this. Would you be able to post up a picture or 2 to show us? I am not as proficient on aftermarket suppliers for this type of modification.

Allthebest and thank you, Paul

[BruceF]

I thought the expansion tank was standard by then. At that time it was a pressurized element. I'm not familiar with aftermarket ones. You can see a diagram of the factory setup here:
https://keenparts.com/CorvettePartsD...4531&year=1970

[Jasper]

Thanks BruceF.
Attachment 1165Attachment 1166Attachment 1167
Paul, I tried to attach some pictures of my set up as you suggested, but I don't know whether my attempt was successful. However, if you follow the link charitably supplied by BruceF you can see the tank and all its connection points pictured there. There is also a line drawing showing a typical installation. The drawing puzzles me because it appears to show a "T" shaped adapter connected to a lower nipple on the tank and the two cut ends of a heater hose. If so, then what is connected to the other lower nipple? Can it possibly make any difference which of the two heater hoses is selected to connect to the tank?

[c4c5specialist]

Hi there,

I will post up a video this evening if you wish. I happen to have a 1972 that I have been working on.

That has the OEM setup on it.

I understand the confusion and will break it down.

Allthebest, Paul

[Jasper]

I wish, I wish!

[c4c5specialist]

Sorry for the delay, been a crazy week. Sunday it will be up.

Allthebest, Paul

[Jasper]

To HeaterCore.jpgToExpTank.jpg

If I got the attached images right, one should show a lower heater hose between the water pump and the heater core. The other image shows the upper end of a coolant line, marked with yellow pencil, which attaches to a lower nipple of the expansion tank. The other lower nipple of the expansion tank attaches to the heater core, also. In short, I have simply spliced the expansion tank into the heater core coolant circuit. It is difficult for me to believe that it makes any difference which of the heater hoses that I cut, but something is definitely wrong (see above). Could my selection of heater hose be the source of my trouble?

[Jasper]

I have noticed that the two heater hoses have slightly different inside diameters. I chose to cut and use the one with the smaller diameter with unsatisfactory results. I now believe that the heater hose with the larger inside diameter is a better fit on the nipples of the expansion tank. Is it worth a try to use the larger ID hose?

[BruceF]

I asked a friend who used to restore Corvettes on a regular basis and this is what he said:

If I understand him correctly, I think he routed the hoses correctly. The only thing he may have done wrong is connect the wrong heater hose to the lower nipples, but I don’t think it would make a difference. I looked in the assembly manuals for 1970, ’71 and ’72 and they do not specify or show which heater hose is connected. They all however show the earlier stye tank, with one lower nipple and a T that connects that nipple to one of the heater hoses. I don’t remember working on a C3 with the later style tank, with two lower nipples, but DeWitts (maker of the reproduction tanks) indicates that the two-nipple tank is correct for 1968-72. He may have overfilled the system - the expansion tank should not be filled with the system is cold. There is a fill line, which is around the half way or a little less point.