Where is my oil return check valve? - PeachParts Mercedes-Benz Forum

showme · #1 11-26-2008, 11:20 AM

I changed my oil last weekend, and put off changing out the lower oil pan gasket because I read a post on the oil return check valve. I have two questions.

A) Does my 81 300D have a PCV valve, and if it does, where the heck is it?

B) Where is the oil return check valve located on this model? What exactly is it's function?

I saw a pretty nice DIY article by dmorrison in the last few days. I'm just wondering if my 81 has the same set up(???) and where do I find that part and also the PVC valve to purchase? (That's once I find the pcv valve location so I can replace it? Thanks for your replies. And Happy Thanksgiving to everybody, too!

fdanielson · #2 11-26-2008, 02:51 PM

There is no PCV valve. On your non-turbo engine the vent hose from the top of the valve cover should be connected directly to the intake manifold and there is no drain tube to the oil pan and no check valve.

Diesel911 · #3 11-27-2008, 02:53 AM

There is an Oil Return Check Valve near the bottom of the tube/stem on my 84 300D that goes down the middle of the Oil Filter Cap. The tube is where I wrote the word "Hole" with a line pointing to the tube. It is hard to see from the diagram but the Check Valve is inside of the Tube a few inches from the bottom of the tube. Oil going through the tube is going back to the Oil Pan by the way of passage "C".

showme · #4 11-28-2008, 02:24 PM

THanks for the replies, folks! I have a little problem of oil appearing on the top of my valve cover, and it has to be coming from either the tube to the breather or the oil cap. I've put two new replacement caps on but I'm still getting it, so I'm not sure where it's coming from. Anybody else had this problem, and if so, what did yo do about it? Lee

fdanielson · #5 11-28-2008, 04:37 PM

The metal oil caps tend to fill up with oil if you turn them over when taking them off. Then the oil runs out all over your valve cover. If you have a metal oil cap take it off without turning it over and wipe it clean. Then you will notice that it is a two piece assembly and how the natural inclination to turn it upside down when taking it off gets oil inside which then seeps out the edge where the inner and outer pieces meet. If you replaced the cap with a used one the gasket my be bad and can be had for a couple of dollars on this site.

There are also commonly leaks where the breather tube connects to the valve cover. At the recommendation of another member on this site I used some high temperature wheel bearing grease on the inside of the tube to act as a sealer where it attaches to the valve cover. After that I used a regular hose clamp instead of the stock spring clamp to re-attach the hose and get a better seal. That helped quite a lot on my car but I still do get some oil seepage.

In the end I don't think you can reasonably expect to keep a 25+ year old diesel engine completely free of oil leaks and seeps. It seems to come with the territory. I know that a number of people on this site have some unnatural ability to keep their engines clean and leak free but for us mere mortals it is really a problem to be managed rather than solved.

showme · #6 11-28-2008, 08:53 PM

Thanks for that reply, fdanielson. That's on my level. And I usually do turn the cap upside down. But the two replacemtents that I've bought have been the newer plastic caps, both out of the box. I will try the grease, though!