Blue smoke out tailpipe but INTERMITTENT - PeachParts Mercedes-Benz Forum

deepbluex · #1 04-19-2004, 07:48 PM

I took my 1983 MB 380SE (195K miles original - engine hasn't been rebuilt) on a trip from LA to SF (about 350 miles each way) and noticed blue smoke coming out my tailpipe when I hit the uphill roads of the "grapevine" (the hills around Bakersfield).

I noticed that the smoke got thicker as I removed my foot off the gas. The smoke lasted about 30 seconds but disappeared as quickly as it appeared.

The car doesn't smoke at all at idle or startup. It also doesn't drip any oil on the ground. The only time it smoked again was on the return trip when I hit some uphill roads.

Is this the valve seals?
Does the incline of the road affect where oil gets into? I don't see smoke when I mash the throttle on flat roads...

How hard is this to fix, if it's a problem at all...
Do the heads need to come off to do this work?

The car runs fine and clean otherwise.

If you have any other ideas, I'd appreciate your input.
Thanks in advance.

Ali Al-Chalabi · #2 04-19-2004, 09:34 PM

If the smoke is due to worn rings/cylinder block, then it makes sense that the smoke would increase as you let up on the throttle. When you use a higher throttle setting, there is a higher brake mean effective pressure in the cylinder that pushes the rings against the wall harder. When the gas is let up, then the rings relax a little more and more oil is passed by the rings and into the cylinder where it is burned. This is why oil consumption will be higher at light throttle/high RPM settings.

Before you go jumping to any conclusions as to what may be wrong, how is the oil consumption? I would monitor it if I were you and see if it is acceptable. If not, then you can start trying to diagnose the problem. Usually it is very hard to wear out a Mercedes bottom end that has been maintained properly. You could try a compression test and see if you get good consistent numbers accross the board.

psfred · #3 04-19-2004, 09:42 PM

On steep grades, oil will "hang" in the valve cover at the rear. It normally drains back down the chain case in the front of the head.

Three posibilities -- worn rings (but you would see smoke at high load all the time, and burn at least a quart in 500 miles all the time), bad valve guide seals allowing oil to get sucked down the valve guides under the conditions you describe (possibly also worn valve guides, too), or bad valve cover gaskets that allow the oil pooling in the valve cover to run out on the exhaust on steep inclines. Hard to tell from inside the car, you will have to look under the hood and check for charred oil in the exhaust manifolds.

If you have excessive blowby from worn rings, there will be large amounts of oil in the air filter housing, too.

Expect to do chain, valves, and guides around 250,000 miles on that engine.

Peter

deepbluex · #4 04-20-2004, 12:58 PM

Thanks for the feedback. I was surprised at seeing blue smoke because the car never smoked before (except for light water vapor at startup on cold days).

The car consumes perhaps 1 qt of oil every 2000 miles. I never see any drips on the ground either. I've been the owner since the car had about 160,000 miles. It now has 200,000 miles. The engine hasn't been rebuilt to my knowledge. When I first acquired the car, I had the timing chain, guides, tensionner, and water pump replaced for about $1,600.

I drive about an equal mix of freeway and city, both conservatively and aggressively. I sometimes mash the throttle but never see smoke, either at acceleration or deceleration.

It's been a very well behaved car as you can see. it's only when I hit the steep uphill roads to cross over the grapevine that I noticed a fairly obnoxious amount of blue-gray smoke coming from the rear of my car. I'm fairly sure it was coming off the tailpipe, not because of leaking oil dripping on hot exhaust manifold parts.

I do think there's something about the "tilt" factor of the car on an uphill path. It doesn't smoke under heavy loads on flat roads but it did on the uphill. I am not sure if it means to the condition of the head.

olpos · #5 04-20-2004, 02:37 PM

some thing an old timer told me, if you use dino oil,when your car burns oil you get blue smoke.
try some mobil 1 syntec oil, syntec does not have any color, and it may also get your valve guide seal's sealing again.
i have seen this work very well.
good luck
rich

haasman · #6 04-20-2004, 02:54 PM

You might want to try Valvoline's MaxLife or other "high mileage oil". It doesn't cure anything but it does seem to improve hard, brittle old valve stem seals, reducing oil consumption.

I have used it in several cars and it does make a difference. Also, the latest version of Synthetics, like Mobil 1 supposedly also have these seal conditioners added.

Haasman

Ali Al-Chalabi · #7 04-20-2004, 03:21 PM

If you are only burning 1 quart per 2,000 miles, then this is well within acceptable limits. It is obviously not burning much oil on level ground then. I would assume then that the bottom end is pretty tight and the valve stems and seals must not be too worn otherwise your oil consumption would be higher. I think your inclination that it only smokes on an incline may be correct. Why that is, I do not know. Hopefully someone else may have more ideas as to that aspect.

psfred · #8 04-20-2004, 07:21 PM

Poor oil drainback can also cause oil to get into the clean air supply line and hence into the air filter, and if you are getting more blowby than the idle air uses, it will get misted into the intake.

Could easily be valve guide seals, which are due for replacement at 200,000 miles anyway. Normal time to first valve job is about 250,000 miles, so start saving your pennies.

Peter

#9 04-20-2004, 10:57 PM

It is probably valve guides, with 200k miles they along with the seals are worn, espeacially the seals. The uphill situation may be allowing the oil in the top of the head to pool toward the back set of valves at a level that is over the top of the valve guide thus allowing oil to flow down the valve stem into the combustion chamber.

Another test is on start-up first thing after the vehicle has been setting for some time. At start up you may get a small quanity of smoke for a brief instant.

Hope this helps,

haasman · #10 04-21-2004, 01:33 AM

If everyone is right about the pooling of oil in the back of the cylinder heads, then the rear plugs should show it.

Pull the plugs and compare them.

Haasman

deepbluex · #11 04-21-2004, 02:23 PM

I'll take out the back plugs to see if they're fouled (regarding the oil pooling to the back of the head when it smokes going uphill). Would the plugs show fouling even if the smoking only lasted less than a minute? It's running clean now that I'm driving on flat ground most of the time.

Regarding the seals - I'll have a mechanic inspect the guides and seals. Does the diagnosis require head removal? What about if I do need new guides and seals - do the heads come off usually to do this job? Does it matter in terms of how big of a job this is?

I'm not sure what kind of cost a valve job would entail on a 84 V8 W126 motor.

psfred · #12 04-21-2004, 06:46 PM

Roughly $4000 unless the head bolts pull the threads out of the block, in which case considerably more as inserts have to be installed in the block.

Peter

deepbluex · #13 04-21-2004, 07:32 PM

That's about twice the value of my car...

psfred · #14 04-21-2004, 11:50 PM

That's one of the reasons it's only worth $2000!

Could be cheaper, but if you have not had the chain coverted to the double type, that will need to be done, and if you have seriously worn valves, you need to replace them along with guides and seals, so with labor....

If you don't need cams and rockers, it's much cheaper.

Peter

psfred · #15 04-22-2004, 09:51 PM

I talked to my friend Hans today, and he said get the valve guide seals replaced. Takes about 8 hrs, so it won't be cheap, but should drop the oil consumption rate to negligible (ie, none added between changes).

Peter