coolant expansion tanks
coolant expansion tanks
so my question is: since the coolant never reaches the boiling point, is the expansion tank even necessary?
english red rat rod 1977 240D, OM617.952 burning B99.9, iron 4-speed & 2.88 diff, 195/60/R14 on alloys, 5mph bumpers, battery in the trunk, 25mm swaybar, 4x ECE H4 lamps, double brake lamps, deleted sunroof, export zoll & california blue plates
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?
english red rat rod 1977 240D, OM617.952 burning B99.9, iron 4-speed & 2.88 diff, 195/60/R14 on alloys, 5mph bumpers, battery in the trunk, 25mm swaybar, 4x ECE H4 lamps, double brake lamps, deleted sunroof, export zoll & california blue plates
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.
Installed:
OM606/722.6, big IC, W220 brakes.
Planned:
DIY manifold, compound, 722.6 controller, built IP.
[i]Less rust.. [/i]
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.
Installed:
OM606/722.6, big IC, W220 brakes.
Planned:
DIY manifold, compound, 722.6 controller, built IP.
[i]Less rust.. [/i]
1978 300D, 373,000km... OM617.912 with a Holset HX30W, 7.5mm IP, 711.113 5 speed (project car, 7 years off the road and counting ;/)
1977 250 270,000km (parts car)
1977 300D (ex 280) 500,000km
1981 240D 498,000
1975 HJ45 ???,000
2001 2.8TD Rodeo 4x2 - 456,000 - DD
Never seen one in person, but I believe the W123s with the tanks had a hose to the bottom of the radiator too
1978 300D, 373,000km... OM617.912 with a Holset HX30W, 7.5mm IP, 711.113 5 speed (project car, 7 years off the road and counting ;/)
1977 250 270,000km (parts car)
1977 300D (ex 280) 500,000km
1981 240D 498,000
1975 HJ45 ???,000
2001 2.8TD Rodeo 4x2 - 456,000 - DD
DiseaselWeasel
04-28-2016, 12:56 AM #4That'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
'82 300D -3" straight pipe, ALDA deleted, 3in1 glowshift gauge, HX30, egr-less manifold, A/W intercooler
'14 Ram 6.7l cummins -G56 handshaker, wishing it was deleted
Nzscott, you are correct. They have a small overflow/blowoff tube, and a fairly large hose that goes to the bottom of the rad
'82 300D -3" straight pipe, ALDA deleted, 3in1 glowshift gauge, HX30, egr-less manifold, A/W intercooler
'14 Ram 6.7l cummins -G56 handshaker, wishing it was deleted
english red rat rod 1977 240D, OM617.952 burning B99.9, iron 4-speed & 2.88 diff, 195/60/R14 on alloys, 5mph bumpers, battery in the trunk, 25mm swaybar, 4x ECE H4 lamps, double brake lamps, deleted sunroof, export zoll & california blue plates
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?
english red rat rod 1977 240D, OM617.952 burning B99.9, iron 4-speed & 2.88 diff, 195/60/R14 on alloys, 5mph bumpers, battery in the trunk, 25mm swaybar, 4x ECE H4 lamps, double brake lamps, deleted sunroof, export zoll & california blue plates
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