Several weeks ago, I noticed (on my 91 300D) coolant leaking near the left front tire. The reservoir was a bit low, so I topped it off and kept an eye on it.

Since then, however, I have not observed any leaking at all; and the reservoir level has remained exactly the same over several hundred miles.

Now I imagine that various environmental factors (ambient temperature, humidity) could account for the expansion/contraction of hoses. But another thought I have is that perhaps the use of the heat could cause a leak. So where does coolant flow when the heat's on where it doesn't flow when the heat is NOT on?

I've been suspicious of my auxiliary water pump for some time, but perhaps there are additional components as well.

Thanks.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Water pump starting to go, maybe?

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Could be the water pump, I had similar situation, a leak then it stopped, then back, then was only little, then the water pump needed to be changed.

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E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...

My w123 did the same thing just before the water pump went out. When the pump did go it was a glorious catastrophic failure. Coolant everywhere; completely emptied the system. You probably don't want to wait, get stranded, or worse overheat the engine.

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)

My SD leaks when parked sometimes when it is really cold it. It is due to the fact that the engine builds pressure when hot, but when it goes back below freezing, everything contracts and loosens up. I have had particular trouble with the little hose below the thermostat housing (OM617), those clamps coming loose. I already replaced water pump before. Try to pinpoint exactly where it is coming from...I would hesitate the water pump expense if you are sure it is coming from the radiator/expansion tank area.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth