Quote:
Originally Posted by Thursday7
Why are all aftermarket coolant overflow tanks sealed (often with their own rad cap)? The OE unit is constantly vented.
Been a while since I studied fluid dynamics, but wouldn't the force of the water coming out of the main rad cap have to be stronger than the force needed to compress the air in the overflow tank (above the coolant) in order for it to work? And conversely, when the system cools, wouldn't it be fighting the force to create vacuum in the overflow tank?
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Your instinct is correct. It isn't really acting like a true proper expansion tank because there isn't a return line for coolant that has been allowed to expand and lose pressure in the tank to return to the cooling system.
https://www.mishimoto.com/engineerin...coolant-tanks/
The typical setup I see is to have a 1.3 bar cap on the radiator and a 0.9 bar cap on the tank, and no return line from the tank back to the system (only a line for hot coolant
to the tank) so it's still acting like an overflow tank, just one that I guess would maintain enough pressure that your coolant typically won't boil in the tank?
Anyway, the majority of aluminum coolant overflow tanks for S-chassis are just ripoffs of ripoffs, the S13 versions all have the same shitty design with the inlet port sticking awkwardly out the bottom for some stupid reason.