Smoke, smell, low oil? - PeachParts Mercedes-Benz Forum

Bimmer-Bob · #1 03-10-2017, 05:43 PM

This morning when my wife started the car (1992 300D 2.5), I noticed what seemed like excessive smoke coming from the tail pipe (in fact, the car normally never smokes at all). My first inclination was that the smoke was blue-ish, but it might have been white, I don't know. Definitely wasn't black, though.

As I started to go outside, my wife met me at the door and mentioned the smoke and a "weird burning plastic smell" that had started on her way home the evening before. So we switched cars and I popped the hood.

The first thing I did was check the oil, I don't know why exactly. It seems the engine has burned a little bit of oil before, and I'm about 300 miles from hitting 5,000 miles since the last oil change (I was planning on changing it this weekend anyway). Oil level was low - not low enough to trip the dash light, and not below the lower hash mark on the dipstick, but right at it. So I added a quart or so.

Coolant tank looks good. It's been topped off to the tippy top since I had it flushed and filled about 8 or 9 months ago, so I know I'm not losing any anywhere. It looks clean, so I know no oil is being lost there.

I had to go to work, so I figured I'd just see how it went. Car started right up, maybe a second of smoke, but then back to normal. Pulling out of the driveway, the acrid burning plastic smell hit me.As I drove down the block, maybe 30 seconds later, it was gone. So far hasn't returned.

No loss of power on the road. Maybe ever so slightly rougher idle, but smooth on throttle. It's kind of hard to tell, though, because this engine always has some clickety-clack to it no matter what. Popping the hood, it does appear that the engine maybe shakes a little too much - motor mounts and engine shock are new, so it's not that - but maybe that's normal for a 25-year old diesel.

Any ideas? Could low oil have caused the smell and smoke? Seems kind of strange. Or is there something more concerning going on? Fueling issues? Maybe bad injectors? I hope not anything more serious than that...

TIA.

atuu2005 · #2 03-10-2017, 06:32 PM

old oil?

jake12tech · #3 03-10-2017, 06:49 PM

How many miles? It's easier to guess when you know the miles. It could be maybe a slightly worn valve seal. Who cares to be honest? It's a 25 year old car. If it uses a little bit of oil between a 5000 mile interval that's pretty damn good. Most cars won't make it past 10 years and be in the junkyard. You bought a Mercedes engineered to last, better yet a diesel.

Your injectors could be a little worn (the nozzles) causing that motor to shake a little bit more than normal. Improper atomization of fuel spraying too much or too little out of the nozzle. You can try a diesel purge, they work wonders. It also tells you if your injectors are worn. If it runs perfect on the purge, and after the purge it runs as it did before, you know you have a worn injector(s). Also, remember an inline-5 cylinder is not a perfectly balanced motor in the sense that it has a odd firing order compared to a 4/6 cylinder. It will never be silk smooth and balance a glass of water off it.

dieselbenz1 · #4 03-10-2017, 07:28 PM

Coolant tank looks good. It's been topped off to the tippy top since I had it flushed and filled about 8 or 9 months ago, so I know I'm not losing any anywhere. It looks clean, so I know no oil is being lost there.

By tippy top are you saying to the cap top?

Bimmer-Bob · #5 03-10-2017, 07:46 PM

Quote:

Originally Posted by atuu2005

old oil?

Quote:

Originally Posted by jake12tech

How many miles? It's easier to guess when you know the miles. It could be maybe a slightly worn valve seal. Who cares to be honest? It's a 25 year old car. If it uses a little bit of oil between a 5000 mile interval that's pretty damn good. Most cars won't make it past 10 years and be in the junkyard. You bought a Mercedes engineered to last, better yet a diesel.

Your injectors could be a little worn (the nozzles) causing that motor to shake a little bit more than normal. Improper atomization of fuel spraying too much or too little out of the nozzle. You can try a diesel purge, they work wonders. It also tells you if your injectors are worn. If it runs perfect on the purge, and after the purge it runs as it did before, you know you have a worn injector(s). Also, remember an inline-5 cylinder is not a perfectly balanced motor in the sense that it has a odd firing order compared to a 4/6 cylinder. It will never be silk smooth and balance a glass of water off it.

Thanks for the responses, guys. Car has 230K on it. I'm certainly not worried about it if the symptoms are attributable to oil level (I just don't get the smell) - I'll just keep a closer eye on it, and consider reducing my interval to 4K miles.

A diesel purge and injector rebuild is on the list, for sure. I don't mind the ticking so much, it's just part of the character of a Mercedes diesel of this vintage, but I wouldn't mind if it shook a little less - not expecting the silky smoothness of a gas inline six, which I guess I've been spoiled by - but it does seem a little bit rougher than it should be.

Bimmer-Bob · #6 03-10-2017, 07:47 PM

Quote:

Originally Posted by dieselbenz1

Coolant tank looks good. It's been topped off to the tippy top since I had it flushed and filled about 8 or 9 months ago, so I know I'm not losing any anywhere. It looks clean, so I know no oil is being lost there.

By tippy top are you saying to the cap top?

Well, up to the neck where the cap screws on.

vtmbz · #7 03-10-2017, 07:51 PM

acrid burning plastic is usually electrical, so don't overthink this.

dieselbenz1 · #8 03-10-2017, 08:21 PM

Coolant level should be at the seam of the expansion tank a max level line exists but is hard to see. Just a side note but the 602 is known to burn coolant when the head gasket goes producing smoke and a sweet sickening smell. Nailing also can accompy this. Just thinking your coolant overflow tank could be filling your expansion tank since no room for expansion?

kerry · #9 03-10-2017, 08:49 PM

My Fuso sometimes has a weird smell for a while after starting cold. It's done it as long as I've owned it. Never have been able to figure out what it is.

Diseasel300 · #10 03-10-2017, 09:09 PM

Are you sure the glow plugs are working? If the engine is healthy enough, it'll start without them, but burp out a white cloud of acrid smelling exhaust until the prechambers heat enough to vaporize the fuel. Had this issue with my SDL when the GP relay was acting up and the smell would about knock you down! Smoke would go away in 15-30 secs depending on the ambient temperature, and wouldn't return until the next cold start the next day.

Bimmer-Bob · #11 03-10-2017, 09:20 PM

Quote:

Originally Posted by Diseasel300

Are you sure the glow plugs are working? If the engine is healthy enough, it'll start without them, but burp out a white cloud of acrid smelling exhaust until the prechambers heat enough to vaporize the fuel. Had this issue with my SDL when the GP relay was acting up and the smell would about knock you down! Smoke would go away in 15-30 secs depending on the ambient temperature, and wouldn't return until the next cold start the next day.

The glow plugs were changed and the chambers reamed less than a year ago. The car actually starts better cold than warm, which is weird.

jltcasper3 · #12 03-12-2017, 11:09 PM

Quote:

Originally Posted by Bimmer-Bob

The glow plugs were changed and the chambers reamed less than a year ago. The car actually starts better cold than warm, which is weird.

Yeah check ur glow plug relay, it may not be working correctly, mine was starting better cold too, the relay was bad.

Maxbumpo · #13 03-13-2017, 02:57 AM

Smoke and rough running after start up are generally going to be either glow plugs or the pre-glow relay. Bad injectors can also cause this.

If you did not install Bosch glow plugs, they are suspect. If you DID install Bosch glow plugs, they are STILL suspect. Bad / defective plugs can happen. Relay can also fail with no warning.

Low oil level has nothing to do with either the smoke at start up or the smell.

Bimmer-Bob · #14 03-13-2017, 02:06 PM

Is there a way to check the GP relay other than just swapping it out? By the way, when I bought the car the preglow light was screwy - didn't come on until after the car was started - new plugs fixed that. AFAIK the relay is original, however.