blue smoke

[firstmb]

Hi

Just joined this very informative forum. Got my first merc recently, a 1988 420 SE, with a lovely 4.2 V8, stainless steel exhaust making a proper V8 sound.

Very happy with the car but have a slight engine issue. I should say it drives very well, there is no loss of power, but on acceleration it blows a big puff of blue smoke when warm. On a cool/cold morning the colour of the smoke is grey.

I have read through the posts on this topic which suggest that the valve stem seals are probably worn - that explains the "occasional" blue smoke.

But, recently when I was stuck in a big motorway traffic jam for 3 hours, practically at a standstill, the occasional blue smoke became a steady stream, and lots of it, it was quite embarassing to keep getting covered in a big blue cloud every time the wind blew in the wrong direction! Very un-mercedeslike.

Once I had got through the traffic jam, the car continued to leave a visible blue streak (visible in the rear and side mirros) which gradually got less and less. Eventually, after about another hour or so of driving it seemed to resume it's normal pattern of blowing only on acceleration from standstill.

The other things I have noticed are:

(1) the oil consumption is well within the guide given in the handbook which says 1.5 litres every 1000 km, it is consuming that much oil in about 3-4000 miles. I check the oil regularly. My trips are mostly motorway driving (90%) and I clock up 3000 miles a month in the merc, at sensible speeds (I won't quote the speed but if I say between 2500 - 3000 rpm you should be able to work it out).

(2) The mileage is 145k, which I gather is nothing for these engines, with service history from MB. The second owner put on 60k miles and didn't service the car as frequently as recommended, although when he did it was at an MB dealership. It has been regulalry serviced in previous and subsequent ownership by MB or independent MB.

(3) My local independent MB specialist told me that it could be anything from the valve seals to worn pistons or bores but that if it passed the MOT and kept going I might as well just keep driving it!

(4) It passed the MOT but only after putting in a "stop smoke" treatment which didn't do a lot in my opinion and certainly is not showing any effects now!

(5) It also idles high, around 1100rpm in neutral, 7-800 rpm in Drive, although this sometimes comes down to about 600rpm. The paper I got with the car shows that the idle control valve was replaced around 2-3 years ago (I'll have to check for the exact date). The owner before me who had it changed also hardly did any mileage in the car, about as much in a year as I'm doing in a month.

(6) I think the pattern of ownership is interesting: First owner did about 60k miles and had it serviced like clockwork, second owner did the same sort of mileage but had it serviced every 15-20k miles, third owner did about 4k miles in 2 years and had it serviced regularly. Then me.

Any thoughts welcome. I'm not a mechanic but it sounds to me like it could do with an engine rebuild. Or is it just a question of getting the valve seals replaced? How much does valve seal replacement cost? How much does engine rebuild cost?

Thanks a lot.

 

[mike65]

Your stem seals are blown, replace and see if that cures the problem, it should unless some damage has been done due to oil loss. Hav'nt a clue about costs sorry.

Mike.

ps does the blue smoke have a particularly noxious pong?

 

[Barnie]

Hi
Yes, I would say your valve stem oil seals being the cause is definate.
I would advise in the short term replacing your engine oil with the new "CASTROL GTX HIGH MILEAGE" this oil has been designed for engines in excess of 75,000miles, & has special addittives to cope with excess oil consumption, however in the longterm consult an MB SPECIALIST to get a price for replacing the seals.
regards. Barnie

 

[stwat]

Definatley the valve stem seals. Seems to be quite common on the v8. I've been sat behind a few around the same age at the lights that smoked a little when stood and then puffed some smoke out when they set off.

I had a 944 that did it for all of the 4 years i owned it :lol: I also tried the stop smoke stuff and it did work,,,,,,,,,,,,for about 2 miles!!!!!!!!!!!!!!!

Like Barnie sais, try some Castrol high milage oil and see how it goes.

I seem to remember, there was some oil addative that was suposed to soften the rubber stem seals so they could seal again. But i never used this cos i was worried about what it might do to all the other seals in the engine.

Stu

 

[Barnie]

Hi
The additive that Stu talks about is contained in the CASTROL HIGH MILEAGE oil, I have found it very effective , in both reducing blue smoke & oil consumption, and after all it is CASTROL !!! WHAT BETTER OIL IS THERE???
Barnie

 

[andy_k]

it doesn't sound like valve stems to me, the symptoms are kind of wrong.

If it were the valve stems I'd be looking for a cloud of blue smoke on initial start up and when you lift off the throttle after acceleration not during. This sounds more like oil being forced into the combustion chamber when the engine is under it's greatest "stress" or when it's hot

My first check would be to have a look at the plugs and see if one (or more) are dirtier than the others then concentrate my investigation on the cylinders affected. My guess would be that you've got a weak piston ring on at least one cylinder but you'll need to get their integrity checked by a garage unless you have the requisite tools.

Also have a look and see if you can find a crank case breather anywhere, if for any reason the crank case is pressurising itself it will force oil back into the combustion chambers causing it to burn, this ties in with your symptoms and a quick check is once you have located the breather, disconnect it and see if that stops the exhaust smoke - you will probably find that the breather pipe blows out a fine mist of hot oil - so make sure you have the end in a jar or something

I'm not sure if your oil system has "flame traps" on it (little mesh filters in the oil breathers) if it has change them, very often overlooked at services they get clogged up and cause the same symptoms you are seeing - it happened to me on a "cough" volvo and aftere I'd worried for a week about needing an engine rebuild replacing a filter for about 50p was a huge relief.

Hope at least some of this is helpful and relevant

Andy

Andy

 

[firstmb]

Thanks for all the suggestions people.

Coincidentally, I tried the Castrol high mileage oil on Friday after I posted the topic (available from ASDA at a relatively cheap price of about a fiver for 2 litres). The car needed topping up anyway (about a quarter from the top of the minimum line) so I'll see if it makes a difference.

There has been less smoke over the weekend but all the symptoms seem exactly as Andy_k suggests i.e.

(1) There is NO blue smoke on starting the car or when lifting off the gas pedal; the problem is definitely worse when the car is warm.

(2) The car does not overheat, typically runs a smidgen below the 80 degree mark on a cool day, just above the 80 mark on a hot day or in traffic, this is when the smoke gets worse.

Can anyone enlighten me as to the "flame traps" andy_k mentions, whether they exist on this model or not (1988 W126).

Cheers (a slightly happier MB owner). I have to say that this model of Merc is fantastically built, the last of the classics. The only other problem I had with it was a slight oil loss from the oil cap, but that was fixed with a new cap (£2.71 from a main dealer!) and hasn't recurred since.