Burns a lot of oil

'80 300SD. No idea what the mileage is. Got the car for a song since it burns more oil than fuel. Has blow-by from hell and pwr is low. Mileage went from 26 to 20 as oil consumption
went up. When the woman bought it six months ago a local shop said the engine was fine. This is a good shop-they wouldn't have let the car go if it was in the shape it is now. The question: what would make this car go from being pretty good to burning lots of oil in six months? My idea: she converted it to biodiesel and it cleaned out all the crap built up around the pistons and the cylinders started leaking. I have not done a compression test yet, but will. Any ideas? Thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I own the same model and mine doesn't burn oil. If your engine's inside is clean and its done < 250K miles there shouldn't be excessive blowby.
Biodiesel 100 cleanses the fuel system and so clogs the fuel filters but that's all it will do. Bio is NOT the problem. Bio 20 doesn't cleanse.
I suggest you check the vacuum pump (located on the front of the engine) which exhausts the air from the car's vacuum system INTO the engine (prior years had a tube to the intake manifold). Excessive blow-by implies a vacuum leak, perhaps from a door lock, the climate control, brake booster etc.. I suggest you test each of these vacuum systems' ability to hold vacuum. Also look for an open vacuum line.
Inside the engine's valve cover is a baffle whose function is to separate the lube oil from the crankcase grasses. The baffle may be clogged and inoperative allowing oil to pass.
Overfilling the lube oil (level s/b between the dipstick's H & L notch) will force oil UP the air cleaner's drain tube on hard acceleration. The paper air filter gets soaked in that event making it difficult for the motor to "breathe". Many shop are careless and overfill.
Sudden oil use could also be from a worn turbocharger seal but that wouldn't create blowby.
The mileage decrease is, IMHO, from preignition of the lube oil and will clear when the oil consumption is fixed. Expect 24 - 25 mpg.
If nothing found from these suggestions a compression test will reveal the motor's condition. Its compression spec. is 319 - 348 psi with 218 psi the minimum with 44 psi allowable difference between cylinders.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You rock, TG. Will report back when i've cked this all out. Thanks. BTW, I really like the burnt copper colour. It was the main reason i went for a look.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Another, less optimistic possibility comes to mind. If the engine was badly overheated the piston rings are shot and an overhaul is the only cure. The climate control "servo" is known to crack its plastic base and the coolant gushes out while one drives. Happened to me but I caught it. M-B sold a lot of replacement motors because of the lousy "servo".
I've now fitted my car with a digital climate control system that eliminates the "servo" and the "amplifier" (logic board).
So if you're buying this car look at the "servo" for its newness.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well, I did buy the car. I will ck the servo. I'm leaning toward the vacuum pump problem since the woman I got the car from is pretty sharp and would have mentioned an overheating session. Secondly, oil is oozing out of a lot of places on the engine--reminding me of what happens when a PCV valve fails on a gas engine. Tho the door/gas cap/trunk vac locks and pwr brakes work well, the engine sometimes takes up to ten seconds before it quits after shut off. Add to that, the engine just runs too well. It starts after less than 10 seconds of glow (46 degrees this morning) and is smooth. This wknd I'll give it a good look. Thanks again and I'll post progress.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
the engine sometimes takes up to ten seconds before it quits after shut off.
The shut down is vacuum powered so a slow shut down like this is symptomatic of a vacuum leak OR, (for future reference) that the shut down device (located in the aft end of the injection pump) is worn out.
I'd first look at the door locks' vacuum circuit.
Good luck.
Tom
'80 300SD w/ 109K miles, owned since new.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Question for TG:
What's the mechanism by which a leak in the vacuum system will create excessive blowby? Does the vacuum pump disharge air go into the crankcase? Seems kind of strange.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yes, read the posts.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ah. It should be instant.
--
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.