Sudden blue smoke from M116.985 engine in 1977 350SE

Started by Berggreen, 28 July 2020, 04:37 AM

Berggreen

Hello,

I have recently bought a 350SE from 1977 with 327.000 km on the engine (M116.985 with K-jetronic), but it has suddently started to smoke a lot and unfortunately blueish smoke, and it smells of burned oil. Also, I can see on the oil pin that it has been eating a lot of oil. 😞

But I am very puzzled, why it has appeared so suddenly. The car has been at the plate shop for some months to have some rust repairs done, and he has had to move it around for an unknown number of times, where he has turned it on and off. But before it went to the shop, it did not smoke like this with blueish smoke, and it also passed the MoD emission inspection in March, before it went to the plate shop.

I only drove it a couple of km yesterday and discovered the smoking, and did not dare to drive it further.

Do you have any clue and/or suggestion what could be wrong with the engine?

Thanx in advance,

Christian
02/1971 MB 280SL (aut.) - olive green 291H
11/1970 MB 280SL (man.) - silver 180G
12/1977 MB 350SE (aut.) - deep green 825H
03/1969 Volvo 1800S (man.) - dark green 94

Randys01

K jetronic's hate being piddled around in garages with multiple cold starts/turn off/turn on.
So best case scenario is you are cleaning out a bit of a backlog of fuel/oil.
However you report the sump reflects oil consumption. So if you combine blue smoke with oil consumption all of a sudden the finger of truth points to a cracked oil ring.
I would rule out valve guide stem seals as these are progressive and u don't see a lot of smoke.

With an engine this old, the compressions are probably variable  and it is very difficult to identify a cracked oil ring by simple compression test or leak down.
The simplest test would be to take the car for a run.  get it hot...pull the spark plugs out and see if one or more are really oily/super sooty. you need to clean the fuel grunge off the plugs so give it a nice run.
If u have an obviously oily plug after this adventure the money says it's a busted ring.

Berggreen

Quote from: Randys01 on 31 July 2020, 02:30 AM
K jetronic's hate being piddled around in garages with multiple cold starts/turn off/turn on.
So best case scenario is you are cleaning out a bit of a backlog of fuel/oil.
However you report the sump reflects oil consumption. So if you combine blue smoke with oil consumption all of a sudden the finger of truth points to a cracked oil ring.
I would rule out valve guide stem seals as these are progressive and u don't see a lot of smoke.

With an engine this old, the compressions are probably variable  and it is very difficult to identify a cracked oil ring by simple compression test or leak down.
The simplest test would be to take the car for a run.  get it hot...pull the spark plugs out and see if one or more are really oily/super sooty. you need to clean the fuel grunge off the plugs so give it a nice run.
If u have an obviously oily plug after this adventure the money says it's a busted ring.

Thanks a lot for your input. It does not sound good. To renovate the engine on these cars does not seem to be worth the money, as the cars are not really valuable. So an engine renovation can easily cost as much as what the car is worth or more.

Getting a replacement engine seems like a better option, although it will destroy the matching numbers, but will probably be more economical.

Thanks,

Christian
02/1971 MB 280SL (aut.) - olive green 291H
11/1970 MB 280SL (man.) - silver 180G
12/1977 MB 350SE (aut.) - deep green 825H
03/1969 Volvo 1800S (man.) - dark green 94

TJ 450

It doesn't sound good but I would be pretty sure it has to do with all the short runs/ cold starts. It's about the worst thing for the engines.

I would change the oil/ filter and take it for a nice long run (a few hundred KM) if you haven't already as the rings may be stuck.

Another possibility for sudden oil smoke could be a loose valve guide, but again I wouldn't jump to conclusions too soon.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500