i have a 67 mustang convertible want to install one of the expansion tanks for the radiator, it is one of the tube one, there is two ports on the bottom, i know one is for the overflow hose from the radiator what is the other one for thank you

 

A drain in case it overheats. I have a rubber hose on the second nipple that routes the overflow to the ground.

Pave the Earth.

 

You should be able to look straight through the top of your overflow (if it has a cap) and see that one of the pipes is longer than the other. The longer pipe allows fluid to drain out of said pipe if the pressure builds up high enough. Just grab a 9/32s hose and tie it so it drains under the car and doesn't get on anything potentially hot.

 

you should not need one if your system cools properly and you have a 14 lb rad cap. but as mentioned one is the overflow for the overflow. . i guess you could use a second tank for that one if need be.

 

It's always nice to have a little bit of leeway with your coolant level. I have heat soak issues in the summer; after I shut the car down, the coolant tends to bubble over into the overflow. It's nice to know I have a reservoir to reclaim it.

 

thanks everyone for the information, my car doesn't run hot but i travel long distances to car show, i feel a little safer with it on

 

Actually, the big boys tell me that if you run the radiator top tank about 1" down from completely full, you won't have any shut down boil over issues. The overflow tank has never solved any overheating issues that I have encountered. My radiator guy said that running an oem tank completely full does not give the system any expansion room, and that causes the overflow tank to catch boil-over. Potential damage to the radiator is always a possibility, also, especially if the cap is not correct or decides not to release coolant. Personal experience does not suggest running the radiator down 1" either helps or hinders cooling; in addition, as stated, the overflow tank does not seem to allow the system to run cooler, either.
Best,
Al