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  #1  
Old 08-05-2000, 01:11 AM
Hisham
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Greetings,

I've just "cyber-stumbled" into this excellent forum and I have a couple of questions to start it off:-

1)At high speed (>90mph), the exhaust would cough impressive plumes of white smoke. No apparent smoke at 70-85mph but I can see white/grey puffs on decelation. The smoke will go away quickly as I further ease on the pedal.

Could this be caused by coolant/oil/brake fluid somehow being absorbed into the engine at higher RPMs? How? Where? Why?

2)The car has a 4-speed manual transmission. While the "stick shift plus Euro M110" combo gives near fantastic acceleration for such
a big beast, I kind of feel that the engine is begging for a fifth gear at >80mph. By the way, the car propels readily on second gear from a dead stop. Is this by design or is it due to non-spec gearing ratios that make (almost)drag race-like 1st/2nd
gear acceleration while foregoing lower RPMs at moderate/high speed?

I appreciate all input.

Thanks

Hisham
Kuala Lumpur
1978 W116 280SE Euro
1995 BMW 325i
1984 Volvo 240GLM
1995 Proton Wira 1.6XLi
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  #2  
Old 08-05-2000, 02:48 PM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I would suspect a ring problem is causing the smoke. It's probably causing such blow-by at that speed/load condition that oil is being blown through the PCV system into the intake. Just a guess.

My wife drove a 126 body 280SEL (automatic) for about 13 years. (great car for her and my old college buddy who's wife currently drives it). We also had a 280TE for a shop car for the same years. The difference is engine noise and rpms at road speeds were significant. The SEL easily would go 100mph. The TE felt like it would blow at 80.

I'm not sure what ratio the 4spd carries but its likely that its lower than the automatic if you have those impressions. The TE had much better low end power and we used it to pull a 19ft ski boat that the SEL had a hard time with. A 5spd definitely allows both worlds; low end torque and high speed operation.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #3  
Old 08-06-2000, 02:33 AM
Hisham
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Steve,

Thanks for your feedback.

As for the 4-speed manual tranny, I can quite easily get a used 5-speed box from a Merc graveyard around here. How difficult/easy(?) is it to retrofit the 5-speed into my W116. Is it a straighforward bolt-on job or do I need to upgrade the rear axle, etc. By the way, would replacing just the rear differential (with higher ratios) achieve the desired result, i.e., lower rpm's at high speed?

Thanks

Hisham

~~~~~

quote:
Originally posted by stevebfl:
I would suspect a ring problem is causing the smoke. It's probably causing such blow-by at that speed/load condition that oil is being blown through the PCV system into the intake. Just a guess.

My wife drove a 126 body 280SEL (automatic) for about 13 years. (great car for her and my old college buddy who's wife currently drives it). We also had a 280TE for a shop car for the same years. The difference is engine noise and rpms at road speeds were significant. The SEL easily would go 100mph. The TE felt like it would blow at 80.

I'm not sure what ratio the 4spd carries but its likely that its lower than the automatic if you have those impressions. The TE had much better low end power and we used it to pull a 19ft ski boat that the SEL had a hard time with. A 5spd definitely allows both worlds; low end torque and high speed operation.




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  #4  
Old 08-06-2000, 09:36 AM
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Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
You would need all of shifter, linkage, & front half of driveshaft to install 5-speed. The trans support is different also. With the 5-speed having an overdrive 5th gear the engine will be turning a lot less rpm on highway.
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  #5  
Old 08-06-2000, 11:25 AM
ColMc
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I don't think blow by will give you white smoke. if its burning oil the smoke will be blue. Too much fuel the smoke is grey/black.

White smoke is more tranny oil or brake fluid


But it could be just carbon burning out of the combustion chambers ....those big engines have a lazy life around the 'burbs so if you kick them , all the plaque gets burnt out of the heads.


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  #6  
Old 08-06-2000, 12:31 PM
Hisham
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ColMc,

You may be right about the carbon being burned out via the occasional freeway driving. Maybe its just a coincidence, but I noticed the smoke only after I've given the 22-yr old motor a couple of doses of STP Injector Cleaner and Gas Treatment. Perhaps the combination of injector cleaner and high speed Italian tune-ups are burning the two decades worth of gunk, hence the ferocious smoke? If this is so, will the carbon deposits (hence, smoke) ultimately "go away."

All feedbacks from this forum appreciated.

Hisham
1978 W116 280SE Euro

quote:
Originally posted by ColMc:
<snip>
But it could be just carbon burning out of the combustion chambers ....those big engines have a lazy life around the 'burbs so if you kick them , all the plaque gets burnt out of the heads.

[/B]


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  #7  
Old 08-06-2000, 12:42 PM
Hisham
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Thanks M.B.DOC,

Since we are on the subject, if I were to replace the 4-speed manual tranny with a rebuilt W116 4-speed automatic (more easily obtained at the Merc graveyard here), what additional modifications/additions would be needed?

Hisham
W116 280SE Euro (screamin' at >80mph)


quote:
Originally posted by M.B.DOC:
You would need all of shifter, linkage, & front half of driveshaft to install 5-speed. The trans support is different also. With the 5-speed having an overdrive 5th gear the engine will be turning a lot less rpm on highway.


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