One hose takes the heat the other is the cooler oil going back. But both hoses may be 30 something years old.

My perspectives are as follows:

- if the cooler is seeping from the lower union, a repair is necessary.
- if the cooler hose fitting is seized to the cooler, repair is necessary.

Neither look good for a remove and replace. Unfortunately these are often seized and MB even sells a fitting kit to replace the cooler fitting with. IIRC it requires drilling and tapping the cooler. Doubtful it can be done in situ.

So then we have some real issues - removal and install, while you’re intending to leave the other bolted in place? I don’t recall the order they are installed off the top of my head, but they’re a pain and the second will “interact” with the first when they’re being worked on. I think you’re setting up for pretty significant frustration if you try to get one out and in with the other bolted on. Moreover, I’m not sure if you can prudently lift the engine high enough to get it around the engine mount with one bolted to the cooler, bolted in place.

Even if you cut out the rubber of the bad one and can finagle it out, and the fittings on the cooler turn out to be good and not necessary to be drilled out, I reserve my doubts that you’ll get the replacement in. It’s just a pain in the best conditions, and you’re implementing a scenario where more challenges and unknowns are happening.

At minimum I’d plan on (gently) disconnecting both lines at their fittings, and be prepared to replace both lines (the “good” one isn’t far behind the bad one). And be prepared for more remediation.

My approach intended to potentially let you leave the hoses connected to the cooler, and make fittings to attach the rubber mid section. Yes, you would be replacing both rubber sections. Yes, it would cost a few bucks for the welding and hose work. Yes there might be some risk with a weeping lower fitting. But the reduced risk of messing with fittings at the cooler, and the relative ease of removing and refitting lines, to me, would be worthwhile.

Thanks for the analysis! It seems more of a problem than it should be.

Replacing both complete lines would be best option. If a local shop thinks they can do it, maybe let them and avoid the frustration.

That will still leave the leak at the bottom union. I think that is metal to metal contact with the soft metal that is likely to be damaged, part of cooler. So maybe the nozzle repair would end up needing to be done anyway. Which as you said, would need cooler to be removed.

My other option is to do nothing for now! If hose blows and engine is ruined, I have one less car to worry about (Only worth about $2k here anyway!)

Maybe see if lower nut can be moved and perhaps reseated to minimize union leak and confirm if getting it off would actually be a problem.

I asked this before - Do I need to completely drain oil or just partly before cracking open that bottom union?

I have removed the oil filter cover so the oil would drain back into the pan leaving only the oil in the lines to deal with.

Ok, so long as there is no oil in filter housing I just need to crack bottom union and collect oil from hoses (and cooler).

I did see a good video here, but it doesn't talk about feeding those lines in and out! https://tinyurl.com/y87hunkn

I bought their wrenches. Nothing special, but it saved me doing the work.

When you get the hoses out or in, you say, wow, that was easy. But it’s only after long periods of finagling them asking how you do it.

As I recall, they really need to get pushed far back in order to go forward.

I bought the lower line from one vendor in Europe. It will take a while to get here, I imagine. They didn't have the upper one. I can get that in Canada - ~C$100 for the Cohline one.

Looks like I need to make a flare from a box end 27mm (or 1-1/16") as well as maybe grind down a smaller one to hold the nozzle at filter end.

If cooler nozzles don't look good, I will have to do the mod.

Once I get the parts, I will have to take car off road for a while or have a shop do the whole thing in a day. Have spare cars, but I took them off road during Covid! Maybe saving in insurance will pay for 300D repairs!

If you proceed with replacing the oil cooler lines, you may want to pull the oil cooler
and clean out the sludge that has built up over the last 35 years.
In advance, I had a radiator shop clean and pressure test a spare junykard oil cooler.

http://www.peachparts.com/shopforum/diesel-discussion/394877-oil-cooler-line-replacement-odyssey.html

Soak the fittings with a penetrant beforehand.
Use slim counterhold wrenches at each union.
Replace the crush washers on the oil filter canister nipples.

I was tempted to replace the rubber hoses on the new aftermarket oil cooler lines with Parker hose,
but ended up just installing the lines without any alterations.
They have been holding up so far.

The toughest part was properly installing the rear clamp by the block.
http://www.peachparts.com/shopforum/...gine-block.jpg

Thanks for the tips.
If I don't need to remove the cooler, might at least backflush it with mineral spirits or diesel fuel or something and see if any sludge comes out. Has a lot of miles on the cooler (less on engine). For 30 yrs I have owned car, mostly highway use, always used synthetic and changed at regular intervals. Hopefully reduced sludge .

I would think there is going to be a pool of what ever you use to flush out the cooler left in the bottom if the Cooler is still attached to the Car. If you flush it on the Car sure to raise the front of the Car so it drains out as much as you can.

I was searching for another thread, and came across this one from 2014. Same problem, same actors 5 or 6 years later.

http://www.peachparts.com/shopforum/diesel-discussion/357774-leak-way-front-driver-side.html

At least I made a small move - ordered a lower hose from a suspect Euro supplier. Hopefully it will come before the hoses blow :)

JHRZ2:
Can either of you or anyone else advise how long those stubby wrenches should be? I would like to just cut the elcheapos I bought in half but not if they will be too short. Talking 1-1/16" and 24mm that will be ground down.(I learned a new term for thin wrenches from a friend who will help - Cone Wrenches!)

Is there any real need to remove that bracket? There are a couple of Youtube videos on line R&R and they didn't do that it seems. Motor mount/shock was removed.

There is a thread where someone replaced the connections at the cooler with AN compression fittings. I had a local fabricator handle the actual change over.

85SD: Working from memory, the threaded section at the cooler had to be replaced with the MBZ threaded repair unit that was still available a couple of years ago. He also put whatever was necessary to connect the existing hard lines. The process was a pita but I'm keeping this car and I wanted the next time to be easy.

The 84SD needed the cooler lines to stop leaking and I simply ordered whatever brand I thought best and installed. The top line comes out 1st and goes in last. That process was also a hassle and I'm hoping it continues to hold at least until I sell the car. The car was on jack stands and the process required lots of turning and figuring to get it to go.

I'm not sure what process I'd use if starting fresh on another car. I'll probably have a chance to find out because I have the newly acquired 85TD that I intend to keep.

I'm trying to make all repairs last 20 years at which point I intend to pay someone else but sometimes I think that I may need to move the time up to 30 years at which point I'll be 97 but hopefully still riding my bike and driving. I'll probably still be cheap. When do you (does one) quit? I have evidence that quiting doesn't necessarily occur at 81 but does change. So, when?

I have sort of quit major jobs at 80+. I hope to have help on this one from a young friend who has a hoist. Same for guide rod mounts job. Maybe axle boots later if need be.

Meanwhile, have done quite a number of smaller jobs on 300D, W210 and R107 while in isolation.

So in other words, you don't have to stop. Just choose your battles :)

On the oil lines, we will replace one or both with new. No mods.

Lower cooler nozzle may be replaced. I have the parts ordered. Bottom one is leaking and that means it is not seating. Fixing the threads may not help if the seat is the problem.

No need to remove the whole bracket.
Only the bolt for the top plate needs to be loosened.

In my case I did not remove the motor mount.
The threaded bolt hole in the lower bracket was stripped.
I had to remove the whole bracket to re-tap the hole for a larger bolt.

Mounting the lower bracket to the block was easy.
Installing the bolt to clamp the top plate to the lower bracket was the difficult part, due to the the tight quarters.

IIRC I used an Allen key to align the bolt holes and needle nose vise-grip pliers to keep the holes aligned.

When I got the car, the tab on the top plate was not mounted into the slot on the lower bracket.
This allowed the oil cooler lines to chafe, thinning the tube walls, which could cause a catastrophic loss of engine oil.