Smoking at Idle - PeachParts Mercedes-Benz Forum

#1 08-14-2003, 11:43 PM

Howdy guys..I have a 87 420 SEL . I just purchased it and have a Question about smoking at idle...seems like if i run dont the highway at 65 for 20 miles it is fine...no smoke..but..if i sit and idle..it will start to puke out a very light blue smoke...and..when i take off, it blows a ton of bluish smoke..but just for about a block..then nothing is noticeble...and..it doesnt smoke upon opening the throttle after a long closed throttle decel down a grade..and.it doesnt smoke at cold start..like over night....any ideas?...car has 210k ..
and....is the 420 close to the 560 in the way you change chain guides and tensioner?..thanks for your help

#2 08-15-2003, 12:39 AM

What weight of oil are you using?

#3 08-15-2003, 12:53 AM

i just bought the car...and havent serviced it yet..but...the sticker in the window indicates 10w30 castrol...i would think that is fine for 90 degree temps in my area..let me know tho

#4 08-17-2003, 12:21 AM

i have driven this car about 200 miles..it just seems to smoke when you let it idle for more than 30 seconds to a minute..if you rev it a few times..it will almost totally disappear...i am leaning towards an injector or two with bad spray making them wash wash the cylinder..does that make any sence?..anyone have anything to add?..i put a can of Techron in the tank..maybe that would do some good...thanks

ArizonaDAK · #5 08-17-2003, 10:12 AM

I had a similar situation with my 560sel and it needed the proverbial valve job....top engine overhaul. If yours hasn't had an overhaul in its history, then it's probably past due...especially if you find yourself always having to add oil.

1991300SEL · #6 08-17-2003, 11:08 AM

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=532110&sortby=lastpost&sortorder=descending

Rockman59 · #7 08-17-2003, 11:09 AM

Sounds to me like it could be the valve stem seals. I had the same problem with my 560 SEL around 110K miles....new seals took care of the problem.

#8 08-17-2003, 06:19 PM

seems to be related to fuel...has a lope feel when it starts to smoke...valve seals would make the engine smoke on a much more regular basis..and..it doesnt smoke after i shut it down hot..restart an hour later with a clean exhaust..guides or valve seals would let oil run into the cylinders and let off a big cloud even after a short time not running..i do live above 5500' and believe it is a bad pattern or something of that nature...thanks for your input

Kestas · #9 08-17-2003, 07:27 PM

I vote for sloppy valve stem seals/guides. What you described is a valve stem seal problem right on the money. Idling is a high vacuum condition for the engine. Most oil is most drawn during these high vacuum conditions past the leaky valve stem bores. When you punch the gas, this oil gets burned up until the next stoplight.

#10 08-17-2003, 09:21 PM

Every engine I have rebuilt that had bad guildes or seals would blow a big cloud of smoke if you let off the gas down a long hill..then punch it..that is alot higher vacuum than at any idle...and..no smoke..clean..it doesnt even smoke at an idle till you sit there and it starts to stumble a bit..just hard for me to believe it is the seals and or the guides..but i have been wrong before.. the only MB dealer in Utah told me to run a few tanks of fuel with Techron in it..thinking it was washing at an idle.... thanks for your reply...i am going to post when i get to the bottom of it.. if it is guides..i would think a total rebuild is in order with 200k on the bottom end..icky..lol.tho..runs like a dream...thanks again

#11 08-19-2003, 09:01 AM

I have been looking for a way out of doing a valve job...i did have dirty injectors and now seems to idle much smoother..but..as many of you have told me...guides/seals are most likely the bad guys..and..i agree...while in the city, with stop and go driving..i noticed a big burp of blue everytime i took off...that finally made me a believer...thanks for all the help..I have parts coming and plan on pulling the heads soon..

Kestas · #12 08-19-2003, 10:04 AM

Have you decided if you'll be doing the bottom end also?

#13 08-19-2003, 02:24 PM

after much discussion with 2 mb techs..they told me that the bottom ends on those engines are bullet proof and they would do a leakdown test to see how the rings are before doing the heads..so..i guess if it passes the leak down..i will just do the heads..

Kestas · #14 08-19-2003, 02:38 PM

FWIW, I recently rebuilt the engine from my 71 Cutlass at 170,000 miles. Not because of wear, but there were a few issues that needed attention. The "straw that broke the camel's back" was a leaky oil pan gasket. I tried to fix just the pan gasket, but it was so much work I decided to pull the engine out. The job mushroomed into a complete overhaul of the engine and transmission. Good thing - because a lot of things got fixed that could have cropped up in the near future (brittle transmission seals, possible corrosion perforation of the timing cover and oil pan). The moving parts of the engine were in great shape, and could have gone another 100,000 miles.

If you have any other "issues" on your car, you may consider having everything done at once.