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1981 Mercedes 300D
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Hiya everyone,

Well I made a trip to Los Angeles over the weekend in my '81 300D and well the car made it down there and back with no major headaches. I noticed that the car used around 2.5 quarts of oil round-trip though! I haven't had much experience with diesels - this is alarming to me...would this be considered normal? I was running the car a good 75-85mph for the whole trip...I know when I run my pickup at high speeds it tends to use up a little oil (half a quart maybe) but 2.5 quarts seemed unusual for the Mercedes. When I got to LA I noticed that the gasket between the intake manifold and the air filter was leaking oil all over the engine...so I replaced it while I was there- it hasn't leaked since. I was thinking that maybe this was the culprit.

I've had my friends drive behind me, they don't notice any blue smoke (or much smoke at all for that matter) coming from the exhaust - and the engine doesn't seem to be dripping it after I replaced that gasket, so I'm starting to think it burned the oil. The car has 197,000 miles on it now, and from what I can tell its the original engine.

Can anyone tell me how 'normal' this oil consumption is? Any other ideas regarding the oil consumption would be greatly appreciated as well! Thanks in advance for the help! Happy motoring!
 

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2x300D-83
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Hi!

I think the problem is that the oil is taking it`s way out through the ventilation ...


Hi!

I think the problem is that the oil is taking it`s way out through the ventilation hose between the cylinderhead cover and the air filter. At that (for an MB diesel) high speeds you will get a high vacum in the ventilation hose. An old air filter will make the vacum higher. Also if the cylinderhead is greasy and dirty the return oil from the camshaft may have problem getting back down. Lift the cover and take a look and make sure you have a fresh air filter.

Anders
 

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1981 Mercedes 300D
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Discussion Starter #3
Hey thanks for the advice! I had my valve cover off less than a month ago to do a valve...

Hey thanks for the advice! I had my valve cover off less than a month ago to do a valve adjustment, and it didn't appear that any of the oil drain holes were clogged or anything. In fact it looked extremely clean there, much cleaner than some other engines I've had apart.

The air filter on my car is about a month old, its still pretty clean. There used to be a rather large oil leak at the air filter housing, but I fixed that when I replaced that gasket between the filter housing and the intake manifold.

I wish I had a compression gauge that would fit the injector opening on the engine, I'd like to check the compression and see if see if maybe the rings and/or valve guides are worn. It doesn't seem to blow any blue smoke from the tailpipe...that's what I don't understand...

Anyway thanks again for the help - if you have any other ideas please let me know! :)
 

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82 300 TD
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Just curious, what viscosity oil are you using? I know with my 300 TD, I use a mineral b...

Just curious, what viscosity oil are you using? I know with my 300 TD, I use a mineral based 15w-40 diesel specific oil. If you have the owners manual look to see if I'm correct, but I know that for these cars a heavier oil is more suitable than the thinner oils that are recommended for cars today. An alternative viscosity would be a heavy duty SAE 30. I personally don't like anything heavier than that because you are robbing the engine of power and making it work harder to overcome the additional friction caused by the heavy oil. I am speaking of like a 20w-50 or an SAE 40 when I mean too heavy. 20w-50 oils generally don't have the correct additive package for diesel engines anyway, so that should eliminate them from consideration. Most 10w-40 oils fall into the same category as the 20w-50 oils as they are not made for diesel duty, the exception being some of the sythetic blends like Shell's Rotella 10w-40 SB. Speaking of synthetics in these cars, unless you have a freshly, and I mean fresh, thoroughly rebuilt engine, don't even go there. These engines generally don't take to the synthetics very well in my experience. If there is any trace of blow-by at all resist the temptation to try a synthetic in your car. I hope this helps. Try Mobil Delvac 1300 Super 15w-40 or Shell Rotella 15w-40 and I think that your engine will be very grateful.
 

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1981 Mercedes 300D
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Discussion Starter #5
I've been using Shell Rotella 15w-40 in my 300D. Same sort of stuff I use at work on th...

I've been using Shell Rotella 15w-40 in my 300D. Same sort of stuff I use at work on the diesel rigs there...we've had good results with that oil - so I figured it was good stuff for me to use on the Mercedes. If I remember correctly, the manual recommended 15w-40 for most climates, so we're doing good there too!
 

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82 300 TD
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Could just be that you have some blow-by and she is just thirsty for oil when run at tho...

Could just be that you have some blow-by and she is just thirsty for oil when run at those high speeds. I very rarely run mine at a sustained 75 mph. I might nudge 75 every now and then but I back off and keep it at around 70 or so. My car has close to 300,000 and does have blow-by. I would say that I have to add a quart every 800 to 1000 miles, depending on how hard I drive.
 

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Discussion Starter #7
Hmm, I guess I shouldn't be doing a sustained 75mph then huh? I've seen so many people w/...

Hmm, I guess I shouldn't be doing a sustained 75mph then huh? I've seen so many people w/ their old 300D's doing it around here, so I figured it would be OK. When I was trying to do an 'italian tune-up', I pegged the speedometer momentarily... I didn't think the car would actually do that! It was amazing how smoothly the car ran after I did this, the idle is soo much smoother and it doesn't smoke as much when its cold now!

I guess I'll relax the pace a bit next time I do any long-distance driving...see if it reduces the oil consumption...
 

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That is a cool pic! I've never had the balls to run mine up to 85. I think 80 is about i...

That is a cool pic! I've never had the balls to run mine up to 85. I think 80 is about it, and you are right . They are amazingly smooth at those speeds and it does loosen up all that soot that God only knows where it hides. How long did you keep it at 85? Too bad that you don't have a tach. I'd love to know how many RPM's it was turning. Mine turns around 3100 at just above 70 mph. I bet it was screaming huh?[8D]
 

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Well I was trying to keep up w/ the pace of traffic in the RIGHT lane of I-5 (you can see ...

Well I was trying to keep up w/ the pace of traffic in the RIGHT lane of I-5 (you can see the other cars waaaaay ahead of me in the pic - they were doing at least 90!), so I think I kept it at 85mph anywhere from 10-15 mins before I decided I'd better back it off to 75mph. I figured that 10-15mins at 85+mph on flat ground, along with keeping it floored at 60-75mph on every uphill grade I encountered was good enough to blow out any crap that was in the engine. Judging from how smooth it runs and idles now, I would say I was right! :)

Strangely enough the engine didn't seem to get much louder past 75mph, but I would guess it was spinning pretty fast! I wish it had a tach - I'd put one in there if I could figure out how to swap one in from a turbo car. I couldn't believe how solid it felt going at such speeds though, definitely impressive! Even more impressive was the fact that I still managed 23mpg with the engine revving that high! Not bad for a non-turbo diesel with 197,000+ miles!
 

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84 230CE & 84 300DT
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I don't think it would be worth the headache to try to swap in a tach from a turbo model. ...

I don't think it would be worth the headache to try to swap in a tach from a turbo model. The tach is electronic and you would have to get all the related electronics that go with it. I have an '85 300D California model with a turbo and I wish my tach would even work. The one time I did get it to work, it caused the transmission to not shift out of 1st or 2nd. I guess the fuse for the tach was blown for a reason. You might consider an aftermarket tach but then you have find a place for it. There are lots of internet sources for tachs and other diesel related items for trucks out there.
 
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