| | | quote | | Originally posted by Will: You don't necessarily have to run a catch tank in back. Just run a lower pressure cap at the rear fill point than at the front fill point. The trapped air will be expelled at the lower pressure cap, but the only place the system will be able to pull water back in as it cools will be at the stock Fiero surge tank at the front of the car. |
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Why doesn't the rear cap also expel coolant? There is no mechanism in a cap to differentiate between air and liquid. Will, in all due respect I think that all the breathing on your coolant system is occurring at the front cap.
I just looked at the cap on my daily driver Geo. There is a rubber gasket on the underside of the cap that seals to the very top of the radiator fill neck. There is a spring loaded seal that seals to the smaller diameter surface inside the fill neck. The vent line to and from the reservior is off the side of the fill neck between the two seals. When pressure opens the spring loaded seal, coolant (and any air in the system) is expelled into the cap. The upper rubber gasket keeps it from leaking to the great outdoors and forces the expelled coolant to the reservior. If the vent line off the side of the fill neck is plugged or the fill neck doesn't have one, then no matter what pressure rating cap is used it is acting as a solid cap.
In retrospect now that I've looked at this closer, the 27-29# rear cap on the Quad 4 was not necessary. Any cap would work since I plugged the vent off the side.
If a flow-through tank is used at a high point in the back of the car for air removal, then it seems like the radiator flow should be reversed so that it is in the bottom and out the top. This way air can get out the top of the radiator and back to the expansion tank.
