Expansion Tank minimum size

[rbryce]

I have a full custom 1968 small block, apx 370 hp. I have a clam shell style nose now and I need to relocate my expansion tank, and would prefer a tank that takes up less space, has only one outlet fitting and has threaded fitting holes, not the 3/4" barb fittings like on the '67 expansion tanks ('68 and above have 5/8" barb fittings, but use 2 of them, which will not work on my car). The Corvette expansion tank holds 2 qts, but that tank only operates at the 1/3 to 1/2 tank level. I have found a wide variety of polished aluminum tanks that serve my desires, but they are all either 1.1/4 qts, 1.1/2 qts or 2 qts. Does anyone know just how big the tank requirements actually are? The 2 qt tank will match the capacity of the Vette tank, but is very large and unattractive. There are many 1.1/2 qt tanks, but the best ones only hold 1.1/4 qts. Remembering the 2 qt Vette tanks operate at 1/3 to 1/2 tank levels, is a 1.1/4 qt or 1.1/2 qt tank large enough, or will I be blowing coolant out during normal operation?

 

[JohnZ]

The midyear 2-quart expansion tank was designed to operate at 1/2-full with a COLD system (19 quarts), so it had adequate capacity to accommodate one quart of expanded coolant with a hot system. If you use a 1-1/2-quart tank and run it with only 1/2-quart in it COLD, you shouldn't have any issues unless your cap isn't holding its rated pressure.