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.