Oil cooler lines on older diesels (especially 616 and 617)

Along with radiator neck failure, the rupture of one of the large oil cooler lines on your diesel engine can easily ruin your engine. When one of these lines goes you can lose all your engine oil in just a few minutes. If you are driving and not watching your oil pressure gauge you can destroy the engine bearings in short order.

Repairs most often mean an expensive engine overhaul. If you use your Mercedes as a daily driver and plan on keeping it for a long time, replace the oil cooler lines unless you have repair records that they already have been changed in the last 10 years. This is a painful job, but worth it for peace of mind.

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Location and access:

The two oil cooler houses are located on the left side of the engine. They run from the forward side of the oil filter housing up to the left side of the radiator where a separate oil cooler is mounted. The lower hose always seems to be the first one to fail. In the first picture below you will see beginning evidence of a leak where the rubber part of the hose is swedged on to the metal neck. When you start seeing oil wettness at these fittings it is time to change the hose/s BEFORE they fail. Also look for v-belt wear in the rubber part of the hose near the power steering belt. If one hose is bad the other may not be far behind. Due to the difficultly and time involved to change them, I always recommend you change both. If you have not done this job before I guaranteed you will appreciate my illustrated instructions.  And the special wrench I make is a must (shown in action in the second picture. Kent Bergsma