JerryH wrote:
If I have a filler with a radiator cap, like this (
https://www.summitracing.com/parts/sme-2202 ), in a coolant hose at the high point in my cooling system, do I need to have an expansion tank or can I get by with a recovery tank plumbed to the side outlet adjacent to the filler cap?
I'm thinking that if I fill it to the base of the cap, leaving no air space, expanding coolant will flow directly to the recovery tank and be sucked back when the coolant cools and contracts.
IMHO, at the risk of repeating others, you do not need an expansion tank. A recovery tank is fine. To prevent the secondary cap from venting, use a 25psi cap. This can be either the filler or radiator, but you can use standard psi caps and tee the ports to the recovery tank. Do not leave an air pocket on the pressure side with a recovery tank.
An expansion tank is essentially an air pocket on the pressure side and does not connect to a recovery tank because the tank would fill the pocket after a few cycles if the system has no leaks (like a bad head gasket). The vent port from an expansion tank goes to the vent port on the radiator neck when there is no recovery tank. A recovery would be redundant.
I used the same filler you have on a 4.3lv6 fiero. I used the common vw round expansion tank on the GO4 interceptor with a civic radiator.
https://www.ebay.com/itm/Radiator-Coola ... ition=1000Dorman makes a good quality overflow/recovery that has enough capacity for just about anything.
https://www.ebay.com/itm/Overflow-Recov ... SwWXhctIl8Tank size should match radiator capacity. For example, I would not expect a stock civic overflow to have adequate capacity to work with a civic aluminum racing radiator, which should hold about twice as much coolant and expand twice as much to reach 200f. There should be just enough coolant in the recovery to cover the end of the hose when the engine is cold and the rad is fully filled. Anymore takes away from the capacity for expansion. Any bottle that can keep dirt out will do.
If heater hoses are the high point (like on my 5.0l 80s ranger), just use a prestone coolant flush kit that has a small inline filler to top.
You only need one cap of course and is doesn't need to be on the rad. This scion racing rad looks promising and about the same price but bigger than the civic racing rad.
https://www.ebay.com/itm/For-04-07-Scio ... 2649033004
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