Oil cooler line replacement odyssey.

[Alec300SD]

Slowly working on getting ‘Stormcloud’ roadworthy by addressing critical maintenance items where failures
can leave you stranded…like the engine coolant system and the oil cooler lines.

‘Stormcloud’ was in major need of repair to the radiator, leaking oil cooler and oil cooler lines.
On the W116 300SD, the radiator and oil cooler are bolted together.
You have to pull the assembly up and out as a unit to repair either one.


Here I’ll cover the oil cooler circuit repair, and the coolant system rehabilitation in a later separate thread.

The old oil cooler was heavily encrusted with external sludge.
Pulled a used oil cooler from PNP and had it cleaned, pressure tested and painted by San Leandro Radiator for $45.
They said there was about a 30 percent blockage of flow from sludge.
The lower oil cooler line had a failed crimp fitting.
Cracks were visible in the rubber sections of both lines.


I had a set of newish oil cooler hoses salvaged from engine out of ‘Rena 2.0 ‘.
The used lower oil cooler hose is the Cohline brand and the used upper oil cooler hose is the Conti brand.
They appeared to be in much better condition than those being replaced.


So, I proceeded to install the refurbished PNP oil cooler and the used spare oil cooler lines.
Removed the old oil cooler lines using slim counterhold wrenches to aid in cracking open the connections at the oil cooler and at the oil filter canister.
Then I removed the bolts of the clamping plates holding the metal oil cooler line sections to the A/C compressor housing and the engine block bracket.


The oil cooler lines were snaked out without removing the motor mounts or lifting the engine.
It is possible, a bit of a pain, put quite doable.
I did have to disconnect the upper vacuum (brake booster) feed line at the vacuum pump to allow oil cooler lines to clear the A/C lines on top of the R4 A/C compressor.

On reinstallation, before attaching the bracket to the engine block, I made sure that the tab of the securing clamp
was inserted into the bracket (the tab was not in the correct place previously).
Replaced the damaged lower oil canister oil cooler hose nipple (the threads were partly ground away)
Installed new aluminum crush washers for both nipples.

The used oil cooler hoses were secured to the oil filter canister nipples, again using a slim counterhold wrench…this time to get the fitting ‘gudentite’.
Was then able to tighten the 10 mm bolt connecting the securing clamp to the bracket.
(Did also replace the missing split ring lock washer for the bolt).

And finally, attached the oil cooler lines to the oil cooler itself.

Unfortunately, a major oil leak ensued from the upper used oil cooler line having lost too much structural integrity.
Evidently a loose clamping bracket in "Rena 2.0' caused excessive thinning of the tube wall from chaffing over time.
Not having rebuildable lines on hand, nor wanting to re-install the old lines,
I ordered a set of new oil cooler lines (Cohline upper and Trucktec lower) from Peachparts.

Once the parts came in, re-did the job a little faster this time.
So far, there are no leaks in the oil cooler circuit.

[ykobayashi]

Sounds hard on the 116. I have this coming up on my newly acquired 85 300d. I have the weepy hoses.

I did my 126 300sd many years ago. If I recall right, I took the hoses out without raising the engine off the mount but then I broke down and lifted the engine to get them back in. While it was possible to do the job without unhooking the mount, it made it so much easier that it was worth the time.

The entire thing reminded me of those kids toys with cords, linked chains, beads and washers that you’re supposed to separate as puzzles. I used to attend parties with my parents where hopeful hosts would give me a pile of those things and hope I’d quietly do them while they socialized. I’m lousy at that stuff but I managed the oil cooler lines in an afternoon.

It was great you salvaged the cooler. I almost destroyed the fittings getting mine out. I ended up (with suggestions from here)using a dremel to cut the old pipe fittings off the flimsy aluminum cooler.

Good job.

[Alec300SD]

It is very easy to damage the soft aluminum fittings on the oil cooler.
There are repair kits availble from MB should the need arise.



When you tackle this job on your 85 300D, spray the line fittings with penetrant a day or two beforehand.


My W116s have a 22 mm counterhold on the aluminum oil cooler fittings, 24 mm counterholds
on the oil filter canister nipples, and 27 mm nuts on the oil cooler lines.

If you position the slim counterhold wrench and the standard size open end wrench on the line fittiing so that they are
about 15 degreees apart, you can squeeze the ends together (like when you lock a pair of vise grip pliers) to crack the union.
Bike shops carry the slim Park Tool cone wrenches (13-24, 26 and 28 mm sizes).

If you don't use the counterhold wrench, you may ruin the oil cooler line or the oil cooler itself.
If the fittings are rounded, where the tools might slip, then it is a better option to split the nut on the oil cooler (as you had done).



Hope this job goes smoothly for you.

[vwnate1]

Good to hear it all went well ~ I was never able to snake the darned hoses out nor in without raising the engine, if I do it again I'll try your tip of disconnecting the vacuum hose pipe .

FWIW, German vehicles almost never use split lock washers, instead they use flimsy looking wave washers that work as well or better then the split typ and never gouge up the surfaces as split washers are designed to do .

[BillGrissom]

If the rubber hoses fail in the future, you can replace just the rubber hose with tubes installed on car. Several posts w/ photos. I used AC hose (5/8" I recall). Oeticker ear crimps look nice. I used an AC crimper. On W123 cars, cut the top hose 1" longer than the factory did (i.e. 15"L) to better clear that evil p.s. pump belt.