Oil in air plenum chamber - smoking engine

1971-1989: 280SL, 280SLC, 300SL, 350SL, 350SLC, 380SL, 380SLC, 420SL, 450SL, 450SLC, 450SLC 5.0, 500SL, 500SLC, 560SL
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Chai
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Oil in air plenum chamber - smoking engine

Post by Chai » Mon 11 Mar, 2019 5:41 pm

My 1974 4.5 litre engine is blowing smoke, lots when taking off after idling in traffic for a while.

I put an inspection camera down the throttle body and can see lots of brown oily gunk coating the inside of the plenum chamber.

The colour and odour is engine oil, not automatic fluid. The auto fluid level is constant, the engine oil needs regular top-up.

There's an oily film rather than obvious fluid inside both breather tubes coming off the crankshaft covers: the fast idle intake and the engine blow-by to air filter.

Is it possible that oil leaking down valve guides can track into the plenum chamber? Any other source for the oily build up?

Chai
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Re: Oil in air plenum chamber - smoking engine

Post by Lance » Mon 11 Mar, 2019 8:27 pm

Blowby caused by worn/broken piston rings causing crankcase pressurisation, forcing oil into air filter by the crankcase vent?
Remove oil filler cap and see if smoke coming out when revved.

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Re: Oil in air plenum chamber - smoking engine

Post by CraigB » Mon 11 Mar, 2019 9:09 pm

idling at lights, or coasting downhill and then lots of smoke and then thinning out, is typical valve seals/guides. Revving and blowing smoke is more rings. You can compression test or better still leak down test to isolate if rings. One of those seal swelling 'stop leak' products might give temporary improvement and help to know if your on the right track.
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Re: Oil in air plenum chamber - smoking engine

Post by Djenka018 » Mon 11 Mar, 2019 9:22 pm

Chai wrote:
Mon 11 Mar, 2019 5:41 pm
...
Is it possible that oil leaking down valve guides can track into the plenum chamber? Any other source for the oily build up?

Chai
There are 2 sources for oil vapor deposits - the pipe-like tube from tappet cover at the front of the LHS cover (goes to CSV) and another pipe tube from the back of the back of the RHS cover going to inner underside of the air filter box.
Vacuum will suck both and there is no fuel to wash it off in the area. Luckily port injectors will wash off the valves and residual fumes will probably dissolve deposits in the manifold and chamber (for regularly used cars)

Cynic would say that this artifact was used as a model for design of the early DI engines and coking of the intake manifold, valves etc...
'80 450SLC 3-continental

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Re: Oil in air plenum chamber - smoking engine

Post by Chai » Mon 25 Mar, 2019 10:20 pm

No smoke/fumes appeared when I removed the oil filler cap and revved the engine. Also none appeared when I removed the pipe from the top of the left hand rocker cover to the idle-air intake with the engine running.

Valve seals must have hardened.
Will report on the oil additive solution next.
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Re: Oil in air plenum chamber - smoking engine

Post by Chai » Mon 01 Apr, 2019 8:24 pm

Poured one and a half containers of a "stop leak" product, the recommended quantity to suit the 8 litre engine oil capacity, and had a 20 minute drive home from the auto shop.
It seemed like the car wasn't puffing white smoke when accelerating off from the lights. There wasn't enough stop-and-go traffic to absolutely confirm this impression but, if a valid observation, signs are good for now.

Car's only driven during weekends so can't provide regular updates.
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Re: Oil in air plenum chamber - smoking engine

Post by Chai » Sun 07 Apr, 2019 12:09 am

Can confirm that the white smoke when accelerating off after idling is no longer present. :dance:

One and half canisters of the Rislone Stop Leak was added - am personally surprised and delighted as I didn't think it would have such a positive effect in a short time. Am also glad I didn't need to buy the "Professional - Heavy duty formula", by the same manufacturer, at five times the price shown here to get this result.
Rislone Stop Leak additive for valve seal.jpg
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Re: Oil in air plenum chamber - smoking engine

Post by CraigB » Sun 07 Apr, 2019 9:47 pm

Good news. I'm trying to remember back to when my old 280s had this issue. I don't think the seal swell is a permanent sort of thing and may have needed to have the additive added again, maybe each change even, but continued to work and i never did get around to changing the seals and possibly valve guides. You will be able to work it out as you go if it starts up again after next oil change. I just remember after it worked so well I had hoped it would have swelled them and stayed that way.
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Re: Oil in air plenum chamber - smoking engine

Post by Bartman4800 » Mon 08 Apr, 2019 9:54 am

What I also found after using this stuff (different brand), is that it dissolves all the gunk in your engine.
My camry started leaking through the oil filter seal after a while. When i investigated it, it turned out my oil filter was completely clogged (and had only been on there for a few thousand km's..


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Re: Oil in air plenum chamber - smoking engine

Post by Chai » Thu 09 May, 2019 8:07 pm

Four weeks later, the exhaust plume after idling a while has recurred. Not as bad as in the beginning but obvious enough.
I'll pour the remaining half-canister into the oil and see how it goes.
Think it's time to consider the obvious - replace the valve seals.
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Re: Oil in air plenum chamber - smoking engine

Post by CraigB » Thu 09 May, 2019 9:39 pm

What mileage has it done Chai? Do you know any history as to when the guides were last done? For me that's the hard part, knowing if you can get away with seals or if the guides are worn and end up having to do it all later - and need to pull heads for guides and a lot more work. Were you planning to use compressed air to hold valves, and release springs? I had been thinking that if i did that on one cylinder (at TDC), I imagine i could release the air pressure (without valves dropping out) and be able to open valve a bit and see how much lateral play in the valve and guide. Then if OK lift them back, put air pressure back to hold them and replace seal etc.

So no answers there but sharing thoughts I have had - tap into any other experience.
Craig Baulderstone
280s's
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280SL Ruby
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450SEL Boris
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Re: Oil in air plenum chamber - smoking engine

Post by AMG » Fri 10 May, 2019 9:31 am

Viton doesn't last forever, and age is the key here, not mileage.

as viton ages it becomes brittle. with irregular heat cycling and use the lubricating oil that normally covers the area is missing during the most critical part of engine operation - startup.

m116/7 valvetrains are not the most 'effective' at using the upper engine lubrication. The design is there and yes it will spray oil everywhere, but that's not how lubrication works..

It needs targeted lubrication to perform it's function.

Now, before the oiler tubes fill up and spray everything, the stem seals are shrouded by a valve retainer, collet and lash cap... and a rocker.

during startup, while your engine had no oil, the 30+ year old seals which were brittle and hard, we suddenly subjected to a rapid abrasive friction from the valve. It tears away the surface fo the seal, and over time and hundreds of starts, eventually the seal has enough lost material to become non-functional - from a sealing perspective. Because of the age and lack or relative use, this extra property of the hard and brittle seal material only serves to exacerbate the situation and a rapid increase in wear is the prevailing condition.

Easy fix, and pretty much every m116/7 that hasn't had top-end work beyond cam oiler tubes clips and cam sprockets will likely need it done.

just notice how damn hard and brittle they are when you remove them, compared to the new ones you put in - you'll see the obvious difference. :cheers:
Current:
1987 560SL 4sp. auto Signalrot "Stella"
1987 190E 2.3-16 5sp. man. Blauschwarz "Hermann"
1992 300CE-24 6sp. man. Perlblau / Iceblau "Gretel"
1992 Range Rover Classic 4sp auto Ardennes Green "Oswald"
2012 E63 AMG Speedshift MCT Diamantweiß "Klaus"
Previous:
1986 560SEL Anthracitgrau "Schultz" - In Mercedes Heaven
1987 190E 2.6 4sp. auto Signalrot "Sabine" - which now resides/owns Andrew M's Garage
1972 350SLC Astralsilber "Lurch" - now in the loving care of Craig B
1989 2.5-16 Blauschwarz 4sp. auto (parted) formerly owned by Derek/Hasan.
2012 Renault Sport Megane RS265 Trophy 8:08 6 sp. man. Liquid Yellow "Jean Rédélé"

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Re: Oil in air plenum chamber - smoking engine

Post by Chai » Fri 10 May, 2019 8:34 pm

The valve stem seals were replaced 8 years ago and the car has been driven 20,000 km over that period.
Car is typically only run once a weekend and sit unused for the rest of the time - leaving time for engine oil to drain away.
Haven't yet considered whether to DIY or let my usual workshop do this.

Options mentioned when I talked about this at the Club general meeting to hold the valves shut were compressed air, or to push a very long strip of cut jeans material into the cylinder through the spark plug hole. For the latter, was said that any cotton thread left behind will burn off.

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Re: Oil in air plenum chamber - smoking engine

Post by AMG » Fri 10 May, 2019 9:54 pm

8 years and 20K sounds a little too soon to be doing stem seals unless they were not correctly installed, or installed with a really ham-fisted approach. So time to look a little deeper.

Now that you've clarified the interval, you should probably investigate the guides and valve stems for wear.
Viton seals should easily last more than that - about 8-10 times that mileage.

It's starting to sound expensive. It actually "might" be worth pulling the heads, and doing a full top-end reco, reface valves, seats, new guides, stem seals, check the springs, retainers, replace hydraulic adjusters / lash caps / followers, maybe even the cams and sprockets..

before you go that far, get yourself a couple of cans of threebond engine conditioner, get the vehicle warm, then pull the sparkplugs, spray it in the cylinders, into the plenum through the inlet butterfly, remove the PCV and AAV/IACV hoses and spray out those, leave them drain, then refit, crank the engine over and restart in accordance with the procedure on the can... it will clean a LOT of the oil out (not 100%, but it will make a massive improvement).

This is standard practice every 10K service interval on most modern vehicles to ensure the PCV and EGR are not contaminating the upper engine. Especially for turbocharged vehicles.

It's such a prevalent issue in subaru's that they have their own branded cans of the stuff to clean the upper cyl at every scheduled service interval. It's worth doing on your M117, since you are aware of the oil residue in the intake.
Current:
1987 560SL 4sp. auto Signalrot "Stella"
1987 190E 2.3-16 5sp. man. Blauschwarz "Hermann"
1992 300CE-24 6sp. man. Perlblau / Iceblau "Gretel"
1992 Range Rover Classic 4sp auto Ardennes Green "Oswald"
2012 E63 AMG Speedshift MCT Diamantweiß "Klaus"
Previous:
1986 560SEL Anthracitgrau "Schultz" - In Mercedes Heaven
1987 190E 2.6 4sp. auto Signalrot "Sabine" - which now resides/owns Andrew M's Garage
1972 350SLC Astralsilber "Lurch" - now in the loving care of Craig B
1989 2.5-16 Blauschwarz 4sp. auto (parted) formerly owned by Derek/Hasan.
2012 Renault Sport Megane RS265 Trophy 8:08 6 sp. man. Liquid Yellow "Jean Rédélé"

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Re: Oil in air plenum chamber - smoking engine

Post by CraigB » Sat 11 May, 2019 9:29 am

Thanks Joe. I haven't heard of that stuff but swear by 3-bond sealants. Many years ago i had a smoky Triumph Spitfire and bought this stuff called Redex on recommendation and poured some down each plug hole and let it soak. Massive difference and was supposed to dislodge deposits that restricted movement of the rings. Disappeared off the market but imagine this could do something similar.

And as to the seals, I don't have experience but listening to others, if guides gone it will shorten life and effect of just replacing seals. Potentially the heads haven't been off the car for 40 years and if its a keeper, doing it now would probably see another 40.... so spreading out that cost over the years makes it look better!
Craig Baulderstone
280s's
280SE3.5
280SL Ruby
300TE Otto
350SL Gloria
350SLC Lurch
450SEL Boris
500SEC's...including Syd
560SEL's Foufou and Zac

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