Author Topic: Smoking 350???  (Read 1921 times)

oscar

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Smoking 350???
« on: 18 July 2006, 05:46 PM »
Hey all, could do with some advice.

I put the car thru some hill tests and was shocked.  Kept the car in 1st/L and accelerated hard for over a second then took took my foot off the pedal.  Kept doing this up a hill then down

UP- Upon hitting the slope there was no smoke whatsoever.  Foot to the ground then off, over and over, nothing.
DOWN- Some smoke on acceleration but come deceleration I thought the rear end had caught fire.
The colour is light blue.
On the flat the smoke varies but nowhere near as bad as what I saw coming down the hill.

Is this a classic sign of something?  I'm hoping it's just the vacuum modulator but I still think the smoke is bluish.
Thanks


  
  

1973 350SE, my first & fave

Nutz

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Re: Smoking 350???
« Reply #1 on: 18 July 2006, 10:34 PM »
Mildly worn valve guides  ??? My W123 280E does the same thing on occasion when you get on the accelerator real heavy for too long in one gear. Every time it happens to me,I think I have blown the head gasket but it soon goes away when I return to driving civilized.

oscar

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Re: Smoking 350???
« Reply #2 on: 19 July 2006, 12:15 AM »
I just can't believe that at the beginning of the year I went to the effort (rather my mechanic did) of getting the valve seals replaced and not the guides. 

I can sustain high revs in low gear uphill without smoke.  Rev down hill then let Low gear slow the car and the smoke gets at its worst.  I thought perhaps this might be blow-by happening.  The angle of the car seems to make a difference as well.

Anyway just did an oil change and put molasses in. ie 25w-70.  I would've put heavier stuff in but I've never gone above 15w-50.  BTW paid $40AUD for an oil filter  :o Bastards!  As for the difference. Mmmm a bit better.

On the flat,  I can accelerate hard forcing a kickdown which'll reveal some smoke before and after.  By the third time I do it the kick down and acceleration is smokeless.

I think until the vac modulator's replaced I'm not going to be able to narrow it down. 
1973 350SE, my first & fave

s class

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Re: Smoking 350???
« Reply #3 on: 19 July 2006, 02:09 AM »
Yes I'm afraid this sounds like a valve guide issue.  When you accelerate hard the volume of air/fuel in the cylinders during intake stroke will tend to prevent oil coming in via the valve guides.  Oil comsumption during hard acceleration is more usually due to oil coming past the rings. 

When youlift off the gas at high RPm the situation is different.  YOur throttle is allowing only small quantities of air into the combustion chamber and so it operates under high vacuum which will tend to suck oil in via the valve guides. 

Sorry. 

Ryan

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

oscar

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Re: Smoking 350???
« Reply #4 on: 19 July 2006, 05:33 AM »
Well that just...... you know.  So, two votes for guides.   :'(  Your reasoning Ryan is spot on.  Last year my compression test showed between 160-170 psi, one cylinder I couldn't test because of a partly threaded hole, but at least the other 7 all held the pressure for about 2 mins each and didn't budge.  All 8 spark plugs discolour the same.  I'm going to have to live with it for a while.  As Nutz said, "drive civilized".
1973 350SE, my first & fave