Ol' smokey

[soates4]

I daily drive my 1974 240d. I work 40 miles from my house and drive it about 500 miles a week. Have driven it to the beach and on several other long distance road trips
The car has never missed a beat. Since ive owned it its always burned a little oil and smokes out the tail pipe. Ive started to realize recently that its getting worse and people sometimes switch lanes to not have to follow me. Any recommendations on how to slow down the death of this worn engine? Its been a tremendous car.

[barry12345]

Going to single grade 40 or 50 oil will usually reduce oil consumption substantially. Has to be used or should be used in more moderate temperature zones or summer/spring/fall/ only.

Although these car were originally straight 40 weight oil cars. 15-40 is not the same. There are at the same time certain defects that will not allow the reduction. Normally oil just too much oil going by the rings is the issue.

It works well for that. It will reduce the oil consumption pretty substantially. Better to extend the life in a well worn engine as well.

Now if the smoke is black it may be fuel if the dipstick does not drop down. How many miles are you getting to a quart of oil now?

[soates4]

I put half a quart in about 2 weeks time. I do run rich but only at high rpm. I have been running rotella 15w-40 in for quite some time now. I live in North Carolina pretty moderate temp. Should i just run straight 50 weight?

[mach4]

A couple of simple things would really help in determining whether you've truly got a "worn engine" or something else that's easily fixable. My suggestions would be

1- Do a valve adjustment - this should be done every 15k miles
2- Do a compression test
3- if the compression is low, add some Marvel Mystery oil to the cylinders and let sit for a day or so to try to free up stuck rings
4- Pop test the injectors - look for both pressure and spray pattern
5- if the injectors are bad replace or rebuild with new nozzles

Another thing to check is the air filter - seriously restricted air flow can cause smoke.

You don't state the mileage on the car...

[Alastair]

Worth changing/checking the Timing-Chain for stretch, replacing the Valve guide-seals and setting the Point-Of-Injection Timing.

All the above can seriously affect the smoke produced, particularly valve-guide-seals, seeing you're using oil.

[mannys9130]

X2 what mach4 said. I'd put the emphasis on the compression test and the marvel mystery oil. These old diesels can get carbon built up on the rings and in the grooves that prevents the rings from moving. On both of my cars when they were down for a little while, I filled the cylinders with MMO and let it seep down over the course of a week. I kept topping it off and letting it soak. Changing the oil drained all the MMO out of the crank case and then I spun the engine with the injectors out to blow any extra MMO out of the cylinders. It fixed a rough rocking idle on the 85.

The thing is, the engine wears out and tolerances start expanding. The expanding tolerances cause more wear and cause oil consumption. To deal with the oil consumption you use straight 50 molasses instead of 15W-40 oil. That thick oil is hard to pump, so it starves the engine of lubrication at start up and it starves it at high rpm (both times when wear occurrence is highest). That creates a nasty positive feedback loop and destroys the engine in short order.

[Diesel911]

If you replace the Valve Guide Seals you will need to do another Valve Adjustment.

"3- if the compression is low, add some Marvel Mystery oil to the cylinders and let sit for a day or so to try to free up stuck rings."
On My Volvo Diesel it took a whole week of soaking with marvel Mystrey Oil and I rotated the Engine and put more MM oIl in and was going to go another week of soaking but but had to get the Car on the Road 3 days later.
If you do they above you will need to change the Oil because you don't want the MM Oil mixed with the Engine Oil.
Also I had no Oil consumption issue. What I had was gray smoke all of the time and worse during acceleration. And, it took about 3 days of driving but the gray smoke went away.

If your Year and Model has a penumatic Governor leaks in the Governor Diaphragm or the Housing (usually around one of the shafts) will cause you to have excess fuel.

Shows old Pneumatic Governor and shows gravity feed drip timing also has pneumatic governor tests
75 240D injection pump oil consumption - Mercedes-Benz Forum

Governor Diaphragm Test
74 240d Grey smoke questions

If your Vacuum Pump Diaphragm is leaking oil gets sucked in to the intake manifold (not 100% sure if this applies to your year and model).