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+--- Thread: coolant expansion tanks (/showthread.php?tid=7181)
coolant expansion tanks - bricktron - 04-26-2016
this 240D had no expansion/overflow tank when i got it: the hose on the nipple under the radiator cap drained downwards. when the turbo engine went in, it acquired a matching pressurized overflow tank from a 300D. about 9 months ago i replaced that with a nonpressurized overflow in the trunk. i calculated that the volume of the hose itself (3/8") was not nearly enough to store the potential expansion of the coolant, so i terminated it in a 2 liter tub. i filled up the hose as well as i could and filled the first quarter or so of the tub with new coolant. this has been working great ever since - temperature is steady, i haven't lost any coolant - but what's in the tub shows no signs of any circulation. still looks brand new. i'm guessing that if it had been mixing bit by bit with used coolant that would have shown.
so my question is: since the coolant never reaches the boiling point, is the expansion tank even necessary?
RE: coolant expansion tanks - Hario' - 04-27-2016
Expansion tank and over flow tank is a completely different thing.
An expansion tank is in constant communication with the coolant fluid to allow fluid to enter and exit as it expands and contracts through heating and cooling cycles, (doesn't have to be boiling to expand a lot!).
An overflow tank is just that, it catches overflowing fluid and does not allow reinjection into the circuit.
Sounds like your 300D expansion tank is plumbed as an overflow tank thus not returning fluid to the coolant system.
RE: coolant expansion tanks - NZScott - 04-28-2016
Never seen one in person, but I believe the W123s with the tanks had a hose to the bottom of the radiator too
RE: coolant expansion tanks - DiseaselWeasel - 04-28-2016
That's not entirely true, Hario. When the cooling system cools down it may create negative pressure - which can, depending on design of the radiator cap - suck spilled coolant back from the catch tank
RE: coolant expansion tanks - MFSuper90 - 04-28-2016
Nzscott, you are correct. They have a small overflow/blowoff tube, and a fairly large hose that goes to the bottom of the rad
RE: coolant expansion tanks - bricktron - 04-28-2016
OK, i should have clarified that only the siphoning expansion tanks are worth discussing here. overflowing into a container that has to be emptied manually is not much better than dumping coolant on the ground. the nonpressurized tank i have in my trunk is designed to allow siphoning back as the liquid cools down. i think i would have noticed if the coolant level in it had risen, but it never seems to move. just not enough desert hillclimbing?