Like so many who have gone before me, I was challenged by oil cooler plumbing leaks on my '83 240D. Long story short, I broke the cooler trying to get things apart, again not unexpected. Aluminum + steel .

Also have another problem, oil t-stat is stuck wide open. Validated that with temp measurements on the plumbing before I made it go tango uniform.

In light of that, I'm entertaining the thought of plumbing motor oil to the bottom of the radiator. I'm doing a new rad anyway (among a long list of other items, car is torn apart underhood), and it's a stick. Old rad had ports that were capped off, new one too.

My '84 Olds 98 and '84 Fleetwood Brougham (both 350 diesels) are plumbed this way. No oil t-stat, just plumbing to a heat exchanger on the cool side of the rad.

I have lots of NiCopp tube and bought all the tools to fab up a new oil cooler hose based off the old one. Thought it's at least worth a try. Anyone ever try it? Wondering if there's any tales of woe on this exercise and support to say NOPE run screaming from it because...

Thanks, Kris.

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1983 240D 4-speed manual

Hmm...the oil cooler was stand alone, the transmission cooler in the radiator will receive heat from the engine coolant. I'm wondering which fluid will get cooler or would it practically be a wash?

Two thoughts, you'd probably be ok without an oil cooler but...??? Consider adding an external transmission or power steering oil cooler instead.

As for the oil T-stat, I think that requires replacement of the oil filter housing.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

True - but that was baked in, so to speak. If the coolant gets warm first, brings the oil up to temp. It's at the cool side of the rad, and the oil t-stat doesn't go fully open until 205°F anyway. As for the oil t-stat, they are replaceable individually, I even ordered one and got it. Predicates pulling the oil filter adapter from the engine and removing a two-pin bore retainer that's staked into the housing. It's been done before. Figuring I might just leave that failed t-stat there and let the coolant bring the oil temp up, and back down as needed.

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1983 240D 4-speed manual

If you don't replace the thermostat yes it would probably heat the engine oil. Looping the cooler lines would probably be ok too, my OM615 didn't have a cooler from the factory. A different motor, but I eliminated the oil cooler on a euro 380SEL in order to use a US radiator, no problems.

Good to know the T-stat is replaceable.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

VWs have an oil-coolant heat exchanger as part of the oil filter housing. Hooking the MB's oil cooler up to an in-rad ATF cooler would likely work ok, though it will increase load on the cooling system since it will be warming the cold side tank.

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Update on this.

I found an NOS oil cooler, like for like, both ports at the bottom, then I found the oil cooler hose made of un-obtanium at a dealer in CA. The oil cooler hose feels too good to be true, waiting on the other shoe to drop, dealer to say oops we don't have it. Cooler looks like a solid deal. Better believe that oil cooler is getting buttered up with anti-seize at those ports. What were they thinking mating steel to aluminum?

That means I need to pull the OFA and get that t-stat out of there. That should be fun. Engine's already supported by a jack stand and some wood. Glad I have a pit to work in and that big jack stand.

Part nos. found: 123-180-03-65, 616-187-06-82

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1983 240D 4-speed manual

Oil to water heat exchangers are common for engines.

That said, they make repair fittings for the OE MB ones, and there are quite a few in the aftermarket.

Frankly I’d be as if not more concerned about the pressure drop/flow design, and the possibility of failure of the connection from the OE cooler hose to the radiator fittings. You’ll need more flex hose.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

Thanks for the insight. I'm happy not having to experiment with the auto trans cooler or having to fab something up.

As expected, the dealer got back to me and said the 616-187-06-82 pipe/hose is no longer available. National back order with no ETA. So I'll either craft one myself or have it done. I do have the one service part pipe/hose (617-187-12-82), so I can practice on the old one before I go for the other. Got the Cohline 15 mm hose and ferrules, bought the crimp tools. Should go fairly smoothly. If I'm unsatisfied, I can always take it to a local hose shop I trust (PRT).

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1983 240D 4-speed manual

You can go to a Parker shop and they’ll mod your oe hoses and fabricate the flex sections. That’s ideal because then you can just swap the flex section.

I don’t think the repair fittings for the OE cooler are anything special. I think some folks have used aircraft fittings.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

Thanks. Visited two hydraulic hose jobbers today (one is a Parker dealer). Each was baffled. Neither had German DIN 24° on hand, except with an o-ring and they said that wouldn't work. Bought a 2nd service part hose that's still available. Will likely use that and my old one to craft a new one.

That said, oil cooler seller contacted me today to say he cannot find what he had for sale. It is hiding in his stash, and if he cannot find it by tomorrow, will refund me. May have to end up bypassing cooler after all . Have to revisit the oil cooler and hoses at a later date. I can't have this thing tying up all my workspace forever.

Got the oil filter adapter off, t-stat is a relatively easy job to do. May fiddle with a pot of oil and a thermometer if I get around to it, verify stat has gone bad. It should extend as it gets hot, push against the spring. Fairly large spring seats that stat in the housing. Used a pair of Snap On needle nose to get that staked/two pin retainer out. Not terribly difficult.

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1983 240D 4-speed manual

Seller lost his NOS cooler, but found me a used one. Getting a partial refund and this used unit. Onward to fabbing up hoses and getting this back together. He sent photos, no damage to the threads at the inlet. He got it apart with two adjustable wrenches. Must be living right, I couldn't get mine apart with heat, kroil and the right size tools. I'll probably disassemble this one and put new O-rings on the base and flush it good. Definitely going to dose the hose connectors with anti-seize .

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1983 240D 4-speed manual

Dose the threads and slide the nut back and dose between the nut and the tube.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Seller came through on oil cooler and refunded a good chunk of $$$. Used, a bit banged up, some fins matted down, nothing severe. Bottom end of cooler in very good shape. Washed exterior and blew dry, straightened as many fins as I could, disassembled bottom of cooler and washed innards with pressurized Varsol, backwards and forwards, no debris. Put new O-rings on it, re-assembled and pressure tested underwater to 90 PSI, no bubbles after getting hoses on nice & tight. Next up, fabricate that one cooler hose made of unobtanium. This should be fun. Photos to follow.

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1983 240D 4-speed manual

Got the hose fabbed up and installed. One of them was off the shelf complete, the other I had to cut the end off a brand new duplicate and install the OE pipe to a new hose with that end on it. The 15mm Cohline hose fit the OE end of the pipe tight, not so much on the other end. I crimped a steel collar over both ends very tight. Feeling good about it. Time will tell. On to the front crank seal and lower oil pan next.

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1983 240D 4-speed manual

Rest of the photos.

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1983 240D 4-speed manual