Okay, maybe a stupid question, but what fluid cools the W123's transmission, engine coolant or engine oil? In other words, what flows through the tranny coller lines... Thanks!

There are no stupid questions, just stupid answers. Transmission fluid flows through the tranny cooler lines to a heat exchanger inside the lower tank of the radiator.

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Keep everything as simple as possible-but no simpler--Albert Einstein

Transmission fluid flows through the tranny cooler lines. The hot ATF is then cycled through the cooler inside the radiator.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

So, if my car is leaking coolant, it's not coming from the transmission cooling lines... RIght? Thanks! I find that the car leaks a bit of coolant in the cold. Don't know why....

That is pretty ambiguous. There could be coolant coming from any number of spots. Mine was dripping from the tranny lines, but I traced it back to a slight leak in the top seam that was running down and dripping off the tranny line.

__________________
Keep everything as simple as possible-but no simpler--Albert Einstein

Well...if the heat exchanger for the ATF inside the radiator is leaking coolant into the exchanger you could lose coolant from a leaky cooler line. However, if that were happening I would surmise your tranny is probably toast. There was recently (like in the past couple days) a thread about minor coolant leaks in the cold. I had a slight drip too when the temps got down to zero. A little tightening of the hose clamps cured that drip.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

So the transmission does cool using coolant, not tranny fluid? Now I'm confused.

odds of the two mixing are very slim in my opinion.

Your coolant leak may very well be due to ambient temperatures. I have had hoses start to leak at very low i.e. 10 degree temps when they were fine the week before.
I'm thinking positive here for you but it might just be as simple as tightening a hose clamp half a turn with a screw driver.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

The ATF is cooled by coolant.

The coolant is not circulated through the tranny, the ATF is circulated through the Radiator inside a sealed heat exchanger.

If this heat exchanger were to go bad, there is a possibility that there could be coolant getting into the ATF. More likely the ATF under pressure would get in to the coolant. The only way coolant would be dripping from the tranny cooler lines is if the exchanger were bad.

While the odds of this happening are slim, I can recall at least four instances of this happening and being discussed on these boards. That is four out of the how many thousands of cars we discuss. Yes slim.

Hopefully that is less confusing.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Technically, there is no tranny cooler, but a heat exchanger.
If it were a cooler it would be independent of the radiator, but as you well know, the tranny lines go into the radiator and they exchange thermal energy with the coolant.
Just a small technical difference.
Thanks, Adam

Thanks guys... I got it now.