Hi every one.


In first place, I apologize for my english language level. I can speak only a little bit.


My name is Armando, and I'm the owner of a precious '91 300E, with 6 cylinders M103 engine, with 120.000 km.


The fact is that some time ago, I detected that after some descents, when arriving to flat road and accelerate, the car smokes a little bit by the exhaust. Everything made me think of valve seals, and I took it to the Mercedes official workshop, where they told me that they had to be replaced, but as the engine also had a typical oil leak through the cylinder head gasket, and the guides could also be somewhat worn, It was decided to remove cylinder head and renew it completely, with leak proof, planned and seats included.


After about 2000km testing the car, it still continues to smoke after a prolonged retention. Immediately I thought that they could have mounted badly the seals (I think they are different the ones of admission and escape) and I went to the workshop to ask.


They assured me that that was impossible, and that they were going to look at the sump (crankcase) ventilation, to see if the problem was in it. After two days with the car there, they call me to tell me that all the work on the head is OK (Although after asking, I seem to have understood that the valve cap was not removed), and after discarding other causes, the motive would be the pistons oil rings.


I was surprised by this explanation, because supposedly, the compression tests were correct on all cylinders. I saw the engine inside myself, and it was as new, which had intact the factory crossed pattern in the burnish of the cylinders walls. They tell me that the first generation M103 (up to the 22,000 engine, and mine is little bit nnoun nº 600), they had "little elastic rings" (low friction against the walls of the cylinders), and that even Mercedes took kits to replace them in the nineties (they show me original Mercedes mico films, arguing for oil consumption in the model).


In consequence of this, the oil rings sweep little oil from the walls of the cylinder, but paradoxically, this contributes to the engine being in such good condition for many kilometers, as it keeps lubricated with a small film of oil on the wall of the cylinders. They tell me that when circulating accelerating this oil evaporates, but that in retention with closed fuel supply valve, the oil accumulates, until expelling it when accelerating again.


The options they give me to finish with the smoke after a downhill, is to change pistons and rings, but the truth is that I do not inspire much confidence, because they did not comment any of this at first.



Perhaps is true, and is typical of the M103 this smoking after a downhill, but I would like a second opinion, before deciding to repair, or even sell the car, because after much spending on it, I'm already starting to be a little tired of "trial and error", to economic detriment.



The car works very well. It is very smooth at idle and running. Approximate oil consumption should be about 3/4 liters per 1,500 km (Valvoline 10W/40). The smoke is only after a downhill without accelerating and lasts only a few seconds. Not much quantity.



What do you think of all this? Maybe I'm a little paranoid about the problem ... or maybe there's no problem. I do not know what to think, so I would appreciate your opinion.
Thank you very much

 

Armand welcome to the forium .
Only thing i can say is when the garage man took off the rocker box did he clan out the two breather holes in the rocker box top .The one is only 2 mm in diamiter .It is all to do with crank case circulation .It works on a loop and all gasses go back in to the engine to be re burnt .Only thing i can think of.

 

Thank you very much for your answer optimusprime.

Supoustly they have checked the crankcase ventilation. I told them about that posibility, but they insist the cause are low compresive oil recover rings. They told me than the piston have three diferent types of rings. One of them cleans the excesive oil deposits in the cylinders walls, and in early M103, that ones were low compresive.

 

You problem must be the valve guides . This will be the oil you talk about going down hill and then taking you foot of the gas .And if smoke comes from the silencer then oil will push out through play in the giudes. The valve in the valve seat must be a nice fit , and pop as you remove the valve from the guide .You say the compresion is good so rings are good .Any wear in the ring or cylinder you would see it in the pressure test .

 

Well. Maybe they have done a bad repair, because supposedly the head was completly renewed, including guides, valve seals, valve seats, gaskets, leak test, etc.

Thats exactly what I thought, but when I told it to the workshop chief, he answered me that the compression rings could be ok, but the oil control rings in M103 first units, came very soft tightened against cylinder walls from origin. Apparently, Mercedes Benz offered the possibility of replacing the piston rings in guarantee in some units, due request of some customers about high oil consumption. It is true that in the current electronic parts catalog (EPC), available pistons and rings appear as replacements for the original ones. even he told me that in fact, that's part of the explanation about the typical longevity of most M103 engines (cylinders allways very lubricated), but in theis point, I don't know what to think about it. Maybe is a real characteristic of the engine, or maybe is just a chinese tale, in order to avoid the "re-reparation"

 

Thinking about this , you engine will burn oil all the time ,at stand still, and on the move if oil rings had gone bad. Go get another second consultation on the problem .Dont just go off one garage say so . Take the car out and put your foot down, see if you spot any oil smoke from the rear .

 

The oil consumption is about a bit less than 3/4 liter in 1500 km.

 

Looks like you having the job of removing head and sump, to remove pistons and check the bore along with replace scraper rings .Or just drive her as she is .Whats the possibility that a thicker oil might help you. What oil do you use now ?

 

I use Valvoline Max Life 10W40

 

Good oil .
But if the head is going to be removed again , dont take it to the same garage .
Then the other people that remove it , can check the slap in the valve guides.
One more thing comes to mind .Pull all six plugs .Then put in the plug hole a quantity of RED X . Or a additive that will remove carbon from the cylinder Turn it over a few times with duster over the plug holes to get it on to the rings .Put another few drops in the plug hole . Leave it for a day . Spin ot over again before you fit the plugs back in or it wont start . But let us know how it goes ,

 

I also think it would be a good idea to change the workshop... the problem is to find a good one where I live. Anyway, I will try.

Thanks for talking about the "Red X", I did not know it. They have supposedly cleaned the chambers in the recent repair, but that's good advice.

The only thing I have clear at this point, is that I do not think it's a good idea to open the bottom of the engine, at least for the moment. It works very soft. I can put a standing coin on it and it will not move, even going up revs. It just smokes after a descent, so maybe a little hasty repair, when the engine is only about 120,000 km (74564 miles).

One thing I had forgotten to comment on, and I do not know if it could be involved on the problem: The gearbox oil was also changed, and a few days ago I saw a stain on the garage floor, which seems to come from the vent. I think maybe it's not related to smoke, but I don't know 100%.

 

All fluids must be at the righ level . Try and get the valves checked as my post .You must start some place ,and it will tell you if they had been repaired .Or just pull the head

 

ok. I will try to find an alternative workshop opinion. Thank you optimusprime.

 

Amand, its bad enough having a problem with the engine . But problems after its been done is a double blow. Good luck .

 

Hi there

this thread is getting quiet old, but I have the exact same problem as you described.

I have a complete new M104 engine, pistons, rings, valve seals… 2000km on it now.
but when accelerating after no-gas downhill i get blue smoke. Only then. Not on startup, not on normal driving and not on hard acceleration.

please tell me if you got this problem sorted if you read this??

thank you

 

So I’m just here because I was looking for general M103 info (new-to-me ‘87 300SL) but I’ve had two very similar experiences with an M104 and an M117, the latter of which was resolved.

What is notable here is that your engine is new. Mine weren’t/aren’t, but in the case of the M104, I “invested” thousands of dollars in a top-end rebuild and dumped even more into various accessory items (EGR, crankcase ventilation, throttle control) until I gave up and just drove and maintained the car until the one of the cylinders gave out. Car was an E320T, USA version.

So I had a very small oil leak—about a US 25-cent-piece amount with a loss of perhaps 0.5 quarts of oil per 2,000 miles. No smoke. I should have lived with it, but I wanted a “perfect” car and went to a now-defunct MB specialist who suggested the top-end rebuild as it was around the time that the head gaskets usually fail. After about two months, the work was done (the car sat with the bottom end exposed for more than a month), and on the test drive, I noted copious amounts of smoke billowing from the tailpipe. The mechanic said that would go away after a time, which it largely did, at least to the point where I never really noticed much while driving the car. After about 500 miles and 1-2 weeks of driving, the oil light went on! I was about 2 miles from the shop, so I drove there immediately to find that the car was low on oil. It was topped off, but no explanation was given. I became suspicious and monitored, noting that the car now had a problem with excessive oil consumption to the tune of 1 quart every 500-800 miles, which gradually worsened. Various excuses were given and parts thrown at the car until I was told by the same mechanic that the bottom end was bad. Why he didn’t check the overall condition of the motor before starting work was beyond me, and he never offered to rectify the situation.

I ended up going to a new mechanic (who still works on my cars) and was advised not to chase this problem further—either to get rid of the car or do basic maintenance and monitor the oil to get some use out of the money I wasted. The motor blew after a couple of years and I sold the car to someone who wanted a fixer wagon.

I later got a 1972 350SL (4.5) and developed a smoking problem as mentioned here without any discernible oil consumption, although the smoking happened at very specific times—one of which was after a descent shortly after the car had been started. I live in a hilly area, and the shop—which is on flat land—could not reproduce my problem. Eventually my mechanic came to my house one morning and followed me down the hill. He was a bit stumped but having witnessed the issue spent a few days thinking about it. He suggested a valve job and promised that he would see to it that the smoking was resolved at no additional charge if the valve job didn’t do the trick. Well, he did the valve job and while doing it noted that only 7 of the seals and guides were not original—one 50-year-old one was still in place and quite mangled at the cylinder on the drivers’ side near the firewall. After that, the problem was solved and the smoking issue disappeared. The car now drives flawlessly and reliably. It wasn’t a cheap fix, but the mechanic stood behind his work.

With my recently-acquired M103 300SL, he noted the typical timing cover leak, which is still very small, and as there is record of the head being redone about 20,000 miles ago (85k, but almost 20 years ago as well), he said to monitor it and doesn’t foresee it becoming a major problem for a long time, reasoning that the cost will likely be the same whether I address it now or later—provided I maintain the car appropriately during the interim.