brucerman

I have a 2008 ML320, 130,000 miles. A sudden oil leak showed up, and it leaked about a quart per mile before i got it home. The leak was coming from the block drain hole, down low, driver's side. The dreaded Oil Cooler Leak! It's apart now, and it has the "old" orange seals - hard as rocks. I suspected, from the volume flow of the leak, that the oil cooler itself was leaking, but I can't find any evidence of that. Don't want to buy a new cooler if I don't have to.

Does anyone know of an 'oil cooler leak' situation, where it was actually the cooler that was leaking? I'm looking for actual knowledge, not a situation where the dealer replaced the cooler, 'just to be sure,' while he was in there. (Cheap insurance, for him, as it was on the customer's nickel.)

Brucerman, in Florida

flybd5

Is your ride a W164 or W163? If the latter, you might have better luck in the W163 forum. If it's an ML320CDI, look here: https://mbworld.org/forums/m-class-w...placement.html

brucerman

flybd5, thank you for the reply. Mine is a W164 ML320CDI. I was already very well aware of Brandon's thread; lots of good information in there.

I have the oil cooler out, and cleaned up. It's made of multiple aluminum plates, probably with channels machined into them, all brazed together, so the water goes between half the plates, alternately, and the oil goes through the other channels. I cannot see ANY gaps between the plates. I sealed my lips over one oil entry hole, put my thumb over the other, and blew hard. no leaks. I don't believe that brazed joints that have been tight for ten years would suddenly spring a leak. Much more likely that the rubber seals would leak.

Bottom line: unless someone on this Forum has evidence of an oil cooler actually leaking, I'm just going to replace the seals - with purple Viton, obviously!

2008 ML 320 CDI

This is not the direct answer you are looking for, but ... I'm in the same position now with an engine oil leak that looks like it is coming from the oil cooler and/or oil cooler seals. I've put in an order for all the parts including the oil cooler itself for US$115 because this repair is a lot of work only to perhaps still end up with the same oil leak afterwards. It's not only a case of the old oil cooler needing to be air tight, but also that the mating surface with the engine block that needs to be perfectly flat. Also, to test for leaks without testing equipment, it's much easier to detect a loss of vacuum than a loss of pressure. Without testing equipment, a test still not infallible, would be to see if a constant vacuum can be held for say 10 seconds between your thumb on the one port and tongue on the other. The oil cooler has presumably been flushed out properly of oil and coolant!

ItalianJoe1

It's unlikely that the coolers leak externally. I have seen them leak, but it's usually by mixing coolant and oil. The leak that you get outside the engine is always the seals, in my experience. '

You could take it and have it pressure tested, to be sure.