Just stop. There is no mechanical or thermal restriction here. This is the way transmission coolers work on almost every car you can think of. Mercedes specified a short drain interval either because they are, what's your phrase? OCD, or because the transmission has some specific issue they felt needed to be addressed. Or, the explanation is that as with so many other things, this happened to be prior art in the Mercedes design room and nobody thought it was important enough to challenge. I'd be curious if anyone has extended their drain intervals, and what the experience was, but that's another thread.

LOL
The lowest temperature the transmission fluid can get to is the temperature of the engine coolant in the radiator.

The transmission internal temperature potential for over heating is totally independent of the engine..... one example being having to ' rock the car' to get it out of a hole... changing back and forth between reverse and low...
Within minutes this can put the trans fluid into the category of needing changing as soon as possible. There is a warning of this in many owner manuals provided with the car..... The need for Trans-x and other varnish dissolvers can be traced to overheating and lack of regular changing of the transmission fluid and filter.


transmission oil cooler - Mercedes-Benz Forum

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

After cleaning up the bits, it seems the transmission cooler nuts may be aluminum. I imagine then the heat exchanger is too. Just hope the dealer nuts are same. Otherwise potential for corrosion. Some aftermarket rads seem to have bronze/brass cooler connections.

I was able to loosen the flare nut. Left hose in place until I get the new nut & washer.

Looked amongst my junk and found that the aluminum adapter that comes with the Bosch primer pump uses same thread. In a pinch, it could be used together with a washer (because the flange face is narrower). No hex either, so would be a vice-grip job Or maybe I could find a nut that fits the exterior thread. (Not planning on doing this unless OE nuts not available! Not even then.)

While waiting, thinking I should look at changing ATF & filter. Questions:
- Does 85 300D have a torque converter drain?
- How much ATF altogether if I drain from pan only or pan plus converter?

OK, I am sure this is here if I do a search (This post by Charmalu seems to answer my questions!)

If I take it up to local shop, what should cost for transmission fluid/filter change come to? Labour shouldn't be much?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

No answers

Anyway, Ordered nuts and washers for rad from dealer (~C$16 for two sets). Also ordered new rad hoses and bought more coolant to refill.

At same time ordered filter kit and bought enough ATF to do the fluid change myself.

Probably get her done next weekend if parts turn up.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

DIY is usually best.

Your parts delivery rates of arrival sound like they are dreadful.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

We are in small town so seldom anything local for these old cars. I could have got the filter kit and hoses overnight, but sources and pricing in Canada can be a problem. Parts are coming from neighbors to South. Shipped this morning and they say they will arrive Thursday. So not too bad. Dealer parts will probably be here today or tomorrow. Will start on draining transmission while I wait.

Interesting that EPC for W123 doesn't show the nuts and washers for the ATF cooler. I have had the car since almost new, so rad is more than likely original. The parts do show on earlier 300SDs and are used on many other models.

Is it possible that pre-1985 300Ds either didn't have the transmission cooler or that the rad tanks were metal and the cooler was welded in?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The most important characteristic of transmission fluid is viscosity, which is temperature dependent. The transmission is designed around the viscosity of the fluid...and the easiest way to keep it reliably constant is to maintain the transmission fluid at the same temperature as the coolant. The design temperature of your transmission fluid is 175-200F, and the transmission will almost never exceed this range. If you cool it below the design point, you will get harsher engagement and rapid wear.

I can't remember what my non turbo radiator with transmission cooler looks like (which has obviously caused some of my confusing comments earlier in this thread!) so I can't comment on materials, but it is an '81 and it does has a transmission cooler section in the radiator. So "pre-85" isn't it.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

You are in Holland.... we naturally assumed ' other' causes.... LOL

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Looks like the radiator bottom in my 1984 & 85 300D. It appears the same basic design as the plastic radiator in my 1996 Voyager and I had a coolant leak there at the auto tranny fitting. The big flat nut had loosened. There is an internal rubber washer that is compressed between the tranny cooler and plastic wall to keep the coolant from leaking out. In my Voyager, the leaking fitting was at the top so I could see what was going on. I expect M-B uses a similar rubber washer internally. This doesn't affect the transmission oil circuit, but you must unbolt the oil tube to replace the big nut (I simply had to tighten mine). Since people are fussing about bad green coolant, I'll go more smug and relate I'm using Evans Waterless in my two 300D's w/ no over-heating and no more corrosion concerns.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Another reason why I would replace the radiator.....its outlived its life expectancy....Next thing to go, will be the nipple that connects the hose to the overflow reservoir.....

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Hey J - You say you would replace the radiator if it was your car????
Somehow I doubt that based on some earlier posts describing your car

Other than a nut that costs a few bucks, there is nothing wrong with my rad. No way in hell am I replacing it until it NEEDS to be replaced.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thanks - Still strange that the nut and washer don't show up on EPC for the W123 rad.

I ordered nuts and washers (for both sides). But I suspect from what you say that the washer may be internal? Maybe they replace those when they recore the rads?

BTW - I have already loosened the coolant unions.

And, after 30 years with out problems, I am staying with regular Prestone green coolant I do change it from time to time. Just did. No noticeable rust or sludge. Hard to find G05 around here, so even if we find some and use it, we have a problem if we need to top up.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Really? I actually did on the 78, radiator was separating....Tracked down one of the last non turbo radiators....The euro radiator, though original is still cooling fine and has no leaks but as it is a 240D radiator....It is an easier radiator to track down, I am also running correct coolant in both cars....

See the 78, has a rebuilt trans in it....and I didn't want to take the chance of overheating the car, and killing the trans....

300D....now DOA....

And we can see, where the transmission lines connect, are made of brass...

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That is interesting. The ones on my 85 are aluminum. Waiting to see what the MB nuts are made of.

PS: Sounds like you NEEDED to change your rad

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5