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jay_bob · #14 10-03-2016, 07:31 AM

Doing the oil cooler seals on my 642 has given me a new appreciation for it. It really is a well thought out system on top of the engine. It looks like total chaos when you first pull off that cover, but everything has a purpose.

The hoses and wire harnesses are all formed to fit back exactly where they came from. There are not a lot of odd brackets and fittings to keep track of. Really only one bracket in the V that ties the drivers side manifold, swirl flap motor, and turbo together, and sits on top of the plastic wire harness carrier.

There are some unavoidable interferences between parts that require you to remove something to get to something else, but the fasteners are all surprisingly easy to access. Even the ones in the back for the turbo.

Someone on the oil cooler thread complained about the different sized fasteners. This is true on the manifolds, there are 19 bolts and it seems there are about 5 different sizes. It's not like a 61x or 60x manifold, there are coolant passages in the intake manifold and it has to support all the EGR self choking system hardware. The thermostat and upper radiator hose connection are actually in the passenger side intake manifold.

The EGR is really what complicates things on the 642. If we didn't have the EGR it would be much simpler on top. There are 3 pieces to the system on a 642, as opposed to the valve on the 61x/60x engines that simply ties the intake and exhaust together. The 642 has the similar function valve, which opens a feed from the exhaust line, but after that, the exhaust gases go to an air to coolant heat exchanger, then to a mixing chamber in front of the engine, before being introduced to the post-turbo and intercooler intake air stream at the front of the manifolds.

Just to show some of the complexity, the intake air path traverses the length of the engine 3 times. First time through the filters, to the bat wing, to the turbo. Then down the big silver pipe to the intercooler. Out of the intercooler into the EGR mixing chamber where the cooled exhaust gases are introduced. Then into the front of the manifolds to be distributed to the cylinders.

To sum it up, having had 4 MB diesel engines, OM616, OM603, OM606, OM642, it is apparent how each one builds upon the predecessor. The day will come when I am going to have to replace the 3 that I have now. I think the engine technology will continue to improve and hopefully MB will keep building diesel - after the VW fiasco I am not so sure - as I really don't want a hybrid due to the high energy electricity involved. Digging into this 642 has given me a new appreciation for the engineering involved and given me a lot of respect for the newer engines.

On the other hand I am not ready for the big brother systems on the newer models. This is what is really dissuading me from buying a newer model. My wife fell in love with the GLC but we realized it was better to spend a couple thousand to fix up the ML and keep driving it especially since it's almost paid off.