1996 E300D- I was driving home last night and the "low oil" light came on. Also I noticed a ton of smoke coming out the back of the car. I pulled over at the next exit and popped the hood. Basically the engine was pissing oil straight up on the underside of the hood, then falling down all over everything including the headers (thus the smoking I saw). I Checked the oil via the dipstick- empty . I refilled it with 4 quarts and the turned the engine on and saw where the leak was coming from- a small crack on this plug looking thing on the passenger side of the engine head, near the front, just above where the water pump attaches. It's about 1.5 inches diameter and 2 inches long. I appears to be a plug inside a plug. The outer plug has a hex nut type collar and the inner plug is an large allen type. The rate of loss was about 1 quart per minute, so I had it towed home. What a mess... oil everywhere and all down the underside of the car and even in the wheels.

Anyone know what this part is? Can I just remove it and bring it to the deal for a replacement. Is anything going to spring out of the head if I remove it? Thanks in advance for your help.

That part is the timing chain tensioner! There is an aluminum crush washer/sealing ring that exists between the tensioner and the cylinder head, it appears that a crack has developed in the washer/ring from your picture! The washer/ring is only a couple millimeters in cross section dimension and mabye one mm thick.

The tensioner assembly is removed with a 27 mm/1 1/16" socket or wrench applied to the larger of the two hex sections of the assembly, the crush washer/seal ring is available from on line suppliers and at the dealership. Hopefully being that you pulled over and shut down quickly after the oil level warning light illuminated you didn't damage anything. It is amazing how quickly 7-8 quarts of oil can be lost at 45+ PSI enen through a small lopening. I'd suspect the opening in the picture with the engine operating and the oil system under pressure expands some.

Thanks,

gosh, how does one go about replacing this washer without messing up the timing chain tension?

edit: OK. quick reply thanks!

How does the tensioner provide tension? is it the inner plug relation to the outer plug? Thus if I just remove the outer plug, replace the washer, and screw it back into the head, then the tension will be the same?

The tensioner assembly operates as a self regulating hydraulic cylinder with engine oil pressure providing the operating force and an internal spring valve assembly providing positioning force when operating oil pressure is absent. There is an oil gallery connection to the tensioner assembly inside the cylinder head, hence the need for a seal ring! The smaller outermost hex opens up the tensioner's internal section and should not be screwed with! If someone where simply removing a working tensioner from an engine that had recently been running; the tensioner is removed using the innermost larger 27 mm hex section, it simply unscrews, put a new seal ring in place, and reinstall the tensioner torqued to 65 Nm. With a new tensioner or in your case now a tensioner that may not have been sufficiently oil pressurized the safe route would be to, take steps to ensure that the tensioner is refilled with engine oil by placing it standing up, plunger end down in enough oil to cover most of the collar now below the large hex. The plunger is pressed to the stop 7-10 times slowly. This will refill the tensioner body with oil and prevent the possibility that the timing chain will be insufficiently tensioned at the first start up possibly causing the timing chain to jump a tooth.

Your later vehicle almost certainly has the most recent updated Tensioner assembly part and therefore uses a seal ring that measures 27 mm ID X 32 mm OD.

If you can find and access an online FSM the tensioner assembly info is located in Section 05.10-310

Thanks for the detailed info. That should get me back on the road!