'68 250S - Clouds of white exhaust, please help! - PeachParts Mercedes-Benz Forum

indigo · #1 04-27-2004, 04:39 PM

I have a 1968 250S (gas, automatic, dual carb) that I bought a few months ago. Recently, it's been spewing large amounts of white exhaust while running. Literally, 15ft high clouds. I replaced the vacuum modulator diaphragm in the transmission (there was fluid in the line) but that didn't seem to make any difference... The smoke is very white and dense, and sometimes doesn't begin forming until the car has been running for a few seconds and the accelerator is depressed. The smoke has a slightly bluish tinge, and could definitely be from oil.

Any information or advice anyone has would be greatly appreciated!

I've searched through the forum and found these:

Smoke!!

Cloud of white smoke

190D white smoke

72 250 - white smoke from exhaust when started

Smokin' like a burning tire...

Tomguy · #2 04-27-2004, 06:09 PM

A great way to tell is to yank spark plugs - if they're oily AT ALL you are burning oil and the most likely cause is worn rings and/or bores. It can result from oil being overy thin too - if you check your oil level and it seems thin, or if it smells heavily of gas when you open the oil filler cap (or when you drain the oil, it looks thin/smells), gas is dilluting your oil causing too much to bypass rings and burn (oil dilution is caused by super rich running). When the smoke becomes as heavy as you're describing, it's usually time for a rebuild, or at the very least, new rings. If it's definetly coming out of the exhaust, oil is undoubtedly entering your combustion chambers.

j9fd3s · #3 04-27-2004, 06:28 PM

look at the pcv system too, id be suprised if it made that much smoke....

cth350 · #4 04-27-2004, 06:41 PM

Then, there's the radiator. With the engine COLD, remove the radiator cap and start the car. bubbles? Refill it to the line and wait for the engine to warm up. Once again, bubbles?

More than likely you're burning oil though.

If you discover you need a new cylinder head, I should have one laying about, as would others on this list. -CTH

indigo · #5 04-27-2004, 06:46 PM

More info:

It's definitely oil... We disconnected the vacuum line from the transmission to discount the possibility of transmission fluid and after a few minutes of running there was a small puddle of oil beneath the exhaust pipe. *sigh*

Also, I forgot to mention:

1.) This was an abrupt problem... Literally, it was running fine and then one morning it just started smoking.

2.) While test-driving it, I've noticed it's losing power, especially on hills.

I'm guessing this would suggest bad rings? I really can't afford to rebuild the engine at this point... Is there anything else I can check?

Tomguy · #6 04-27-2004, 07:07 PM

What you're suggesting sounds like one dead cylinder due to either ring or piston failure rather than gradual wear of rings and bore.

I would imagine, with all that oil being burned, that it misses. Find out which cylinder it's missing on and do a compression test.

You might even have a burnt piston (which would be better than replacing rings on 6 pistons, having to remove 1 is much less of a hassle). I don't know if it even happens on MB engines or not. Is it possible that something really hard (cracked valve, stone?) got into one of the cylinders and marred the bore to the point where oil flows freely into it and out the exhaust?

indigo · #7 04-27-2004, 08:29 PM

Sadly, you're right... Except that _two_ cylinders failed the compression test. (We later determined it was probably the rings in those cylinders.)

:-(

At this point, I have neither the money (starving student) or the time (about to take my finals and then leave for an internship) to properly rebuild the engine so I'm parking it until later this year.

Thanks to everyone for their help and advice! It was a big help.

Tomguy · #8 04-27-2004, 09:22 PM

What was the compression? If it was around 80 or less it's more than rings!

indigo · #9 04-27-2004, 09:55 PM

The compression was 80 and 90 on the two bad cylinders. Although, it was only 140-150 on the good ones... *chuckle*

Like I said, it'll be a fun (and expensive) project for later this year.

cth350 · #10 04-27-2004, 11:42 PM

shortest path to a solution is to get another straight 6. Any one will do. If it's another M114 engine, then you can recycle the transmission. Otherwise, geta a 280S engine+tranny and swap it in. -CTH

psfred · #11 04-28-2004, 12:41 AM

Two adjacent cylinders low? Bad head gasket.

Lots of oil consumption too, problaby rings or cylinder bores, although a loose valve guide will do exaclty the same thing -- lots of oil going down the hole, and lousy compression because the valves don't seat.

Worth checking, since it's not anywhere near as expensive as an engine rebuild.

Peter

Mark DiSilvestro · #12 04-28-2004, 08:42 AM

One last thing to check before condemning the engine - possible brake fluid seepage from the brake master cylinder causing fluid buildup in the power brake booster. Over time, if enough brake fluid accumulates, it's sucked through the brake booster vacuum line and burned. Lots of white smoke. I saw this happen on a friend's '71 BMW 2800 and my '67 Sunbeam Alpine. The guy who sold me the Alpine thought it had a blown head gasket.
Disconnect and plug the power brake booster vacuum source. See if the smoke goes away.

Happy Motoring, Mark

autozen · #13 05-11-2004, 05:54 PM

Mark, you have a point with the brake booster, but he has two low cylinders, and if they are adjacent, Peter is right with the failed headgasket. If water is entering the cylinders, it is turning to steam and causing white smoke. The temp gauge should show abnormally high temps.

Peter