Manual transmission issues aside, here is my last problem with my 1983 240D. I had new valve stem seals ($400) put in a few weeks ago to stop the oil burn rate of 1 qt every 450 miles. I left instructions that if in their professional opinion the seals alone would not solve the problem, to go ahead and do a complete valve job. After I got it back and testing it, I am still burning 1 qt per 450 miles. The new seals didn't do an ounce of good.

I have good compression - 400 in 3 cylinders and 380 in the other. Questions:

1. How can I tell if the mechanic actually did the job I paid for? I can't see any visible signs that the bolts were removed to the valve cover or the throttle linkage was removed. If I remove the valve cover, can a person (remeber I'm not expert DIYer) tell the condition of valve seals, if new seals are installed?

2. Can oil rings be bad and still have the above good compression numbers? Is there an easy miracle juice or fix that will help oil rings expand? How about valve seals?

3. Should I have a complete valve job done? Would a valve job solve the oil burn problem or would something more need to be done such as a ring job or total rebuild?

The car runs fine every day, no oil leaks on the driveway, starts right up, shuts right down, it's just all the death threats I get from the people behind me in traffic that bothers me!

Thanks, Tim

It is my opinion that you do not have a ring problem if you have that kind of compression. They would have had to pull the head to do a complete valve job.

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Jim

I only had the valve seals replaced (or I paid for), still don't know if they actually replaced the seals since absolutely NO change in oil consumption, still 1 qt per 450 miles. Thanks, Tim

What kind of mileage on the car....

Sounds like you have worn piston rings, you have good compression because the oil leaking past the oil scraper ring, gives the compression rings a better opportunity to seal in the cylinder.

I just went through the same thing with my 300D, I was using 2 quarts every 500 miles. Valve seals won't cause that big of an oil consumption problem. Usually the valve seals only cause smoke at start-up because the oil actually has a chance to seep down past the seals when the engine is not running.

At best valve seals may cause a quart useage every 1000 to 1500 miles, if that.

Hope that helps a bit!

Brandoncrone,

My car has 142K on it. So what was the result of your 300D, did you have a valve job done or a complete rebuild?
Thanks, Tim

Brandon - I was under the assumption that if you have good compression then the bottom end should be in good shape. Goes to show - you learn something every day .

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Jim

Tim the Taxman:
Not to start another thread here...but what kind of manual transmission problems are you having?

I grind whenever I go into third gear. Have been told by 2 independant techs that it is the synchro. Double-clutching only works from 2-3 and not from 4-3.

I have been told by several here that it doesn't sound like the synchro... what to do.

Your probs similar?

__________________
Current: '91 300TE 4MATIC 317k and climbing...
Former:
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)

"Never sweat the petty things...
and never pet the sweaty things."

dieseldaddy,

I have another thread going on my transmission called "manual transmission noise and vibration problem". Basically it buzzes. No problems going into any of the gears, it shifts fine, just vibrates and buzzess loudly. When it occasionally stops for a few seconds (instant on, instant off) during my drives, WHAT a difference, VERY quiet in the car (diesel speaking). Two mechanics didn't know what was causing the problem. The last one replaced flex disks and driveline ($800). That was NOT the problem, but on the bright side I have a new driveline AND I don't need to bother myself with questions like "I have $800, what should I do with it?"

Well, I took the cheap way out, disassembled the engine found that the liners were shot, pistons badly scuffed, and two cracked oil rings. I found a used motor with 150k on it for $350. Couldn't beat it, it was going to cost 3 times that to rebuild the one I had with 250K on it (My odometer stopped working while the previous owner had it, for about 5 years!)

It was the easiest way I thought, get an engine with low mileage, never had human hands into it since it was built....figure it should last longer than the car.

Yes and no on the good compression.....a dry cylinder will give lower compression readings than a cylinder lubed with some oil, the three cylinders he has that are around 400psi are probably the ones that have the problem. If he were to remove all 4 glo-plugs he probably find a lot of ash on the ends of them from the oil useage. Valves don't leak that much oil even with bad seals. If I am not mistaken specs on the compression is around 350psi. 400 just seems awfully high to me, especially with 150K on the engine.

Dieseldaddy.....

Bad syncros my friend, unless by some small remote chance the clutch slave cylinder is failing and the disc is not being released enough, but if that were the case you would have trouble getting it into 1st and reverese.

The syncros slow the speed gear down or up to force them both to spin at the same speed allowing smooth engagement into a gear. Say you shift from second to third, the 3/4 syncro has to speed up 3rd gear to the speed that 2nd gear was at, when the syncros are worn they don't do that and that is where the grinding is coming in, 3/4 syncro hub is grinding against 3rd gear until the speeds of the hub and gear are the same.

End result, replace 3rd gear, 1/2 and 3/4 syncros, 3/4 syncro hub, check the bearings in the trans, lots of metal running around from all the grinding.

Sorry nothing but bad news, have rebuilt lots of standard transmissions.....they have a lot of hard wearing parts!

Brando and engatwork,

Now I am slightly confused. If I have good compression can the rings still be bad? If that is correct, then I need a complete engine rebuild? This is beginning to sound like the never ending repair story. How much $ will it take to solve my smoking problem?

Is it better (or cheaper) to get a used transmission or have my transmission rebuilt? Seems to me a used trans might have the same problem. Medi the mechanic said he could replace my transmission with a used one for $500 installed.

On the smoking problem, with bad rings, this sounds like a complete overhaul or replace with a rebuilt. What is this going to cost roughly? I'm beginning to doubt my car, my wife wants me to just go buy a new car. I really like the 123's and 115's, but this car is looking like a money pit. It is getting harder to convince my wife they are great cars!! On the other hand, what else could go wrong after if I rebuild? I've already replaced the driveline and timing chain, that last one may have been for naught in a rebuild case, bummer!

Its hard to explain, Yes you can have good compression with bad rings with a heavy oil consumption problem, the excess oil is giving the compression rings a better seal to the cylinder walls. There are three rings on a piston. The top is the main compression ring, the second one down from the top is the secondary compression ring and the third down is called the oil scraper ring. The problem is with two things, the compression rings on a diesel are very stiff and that is why they have cast iron liners for the cylinders. The problem is that over time, and especially from lack of regular oil changes, the cyilnder wears out (Gets bigger in diameter) and the oil rings are very light tension and they can only spring outwards a little bit. When the cylinder get too big they loose tension with the cylinder walls and allow excess oil to get into the compression rings and eventually into the combustion area and is burnt.

You have a good running engine by the sounds of it, good compression, so you can probably get by with new liners, pistons and rings. Maybe you can even reuse the old pistons, depends on what they look like.

Roughly a grand as a worst case scenario, without replacing any main bearings on the crank. You have to replace just about every gasket in the engine, might as well replace the front and rear crank seals. You can get everything you need from Fastlane or Performance Products. A machine shop will have to install the liners and bore them to the size of the pistons.

As far as the trans goes, probably better to find a used one, I have never personaly rebuilt a MB standard trans, there isn't much to them, but finding the parts is the problem. I'm sure you could get them at the dealer, but will pay the 'star' price for them!!

Its tough convincing the wives!!! My has a lot of doubt too, of course this car never had a lick of maintence done to it until I got it around 175,000. Still had the original rear diff fluid!! They are good cars, they do require a lot of upkeep....

While I am good at fighting the taxman, I don't have the space, tools, or know-how to do the repairs myself, so I am at the mercy of the mechanics. I wish I did have all of the above! Having a mechanic do the jobs, is there anything else from the above (new sleeves, rings, possibly pistons, used trans) that would be a good idea to have done? Valve job? Would it be cheaper to get a rebuilt? Here is where my wife starts in on the "throwing money away" discussion!!

Yes my car runs fine, other than the high oil burn. No leaks, starts & stops fine, A/C runs cold. Commute is 24 miles each way at 70-75 when I can, crawl at 2-5 in trafic (SF bay area)

Taxman

If you do a purely economic analysis of this problem, which I'm sure you'd appreciate, the answer is to keep driving it as is. I am assuming it is blue smoke you are blowing, not black. If black, you could have other problems that are causing the oil to burn, like injectors washing down the cylinders.

If it is burning oil (very blue smoke) I would continue to drive it and maybe try putting some type of treatment in the oil to reduce the consumption. I'm not a big believer in oil treatments, but it sounds as if you have little to lose.

Given the other problem with the car, I wouldn't put any more money in it. I would drive it and look for another one in better shape for $2000.

Just an opinion.

Joe

Tim the Taxman,

With the oil consumption rate you cited, you should see quite a bit of smoke when the conditions for burning the oil occur. I am curious, does the car burn more oil at rest than under load? Meaning, when you are idling or coasting, does the smoke seem thicker? Or is the smoke worst when you are pretty heavy on the throttle? Oil smoke is usually blue but if you have an unusually high consumption event, it can be white. Black smoke is usually unburned fuel.

I would look for ways to get oil into the combustion path that does not involve rings or valve seals. In a Diesel, the intake manifold rarely sees a vacuum (which is why Diesel engines have vacuum pumps), so the conditions on gas cars that link valve seals and oil consumption are not quite the same on Diesels. Seal leakage on Diesels usually leads to a build up of carbon deposits on the back side of the valve poppet. Eventually it leads to seating and clearance problems, which show up as hard starting and low compression.

I am always a little amazed at 20 year old cars with a new 22:1 to 24:1 compression ratio that can generate over 350 psi in a compression test. One atmosphere is 14.7 psi, so 22 times that is 323 psi and 24 times that is 352.8. According to my engine manual, the engine is "ok" as long as the min and max values are within 45 psi or so, and no cylinder is below about 221 psi. And turbos have about an 18:1 ratio with the turbo "at rest" which is usually the case when taking a compression reading. It seems to me they should be about 260 or 270 psi.

Anyway, if you have really solid starting and running in all weather and are also smoking and consuming oil, I would be inclined to think you might have a vacuum pump diaphragm, or other vacuum connection that is drawing oil into the engine. If the vacuum pump diaphragm fails, the oil consumption at idle or when coasting can be spectacular, as well as ominous. If it is leaking but not completely ruptured, it will also provide a good leak rate, directly into the intake manifold via a long white translucent tube from the front, lower driver's side (USA) of the engine to the intake manifold. This line will be dark or black instead of the translucent white when all is well if there is oil inside it.

There may be some other vacuum and oil combinations that can lead to sucking oil into the intake, or some other issue with a leak path to either manifold through a bolted connection. So, before I would go as far as taking the head off or something else to check the condition of the cylinders (which I would do or have done before I junked the engine), I would check the connections to the intake and exhaust manifolds, the vacuum lines and then remove the air filter and housing to get a visual inspection of the intake manifold. Engine oil is black and is very obvious.

If you suspect the shop you took the car to did not actually change the valve seals, I think you should get another shop to do a compression check and give you a call on the state of the seals. They might also be more capable of identifying the path your oil is taking to being liberated from the engine, as well as what is causing the smoke. Good luck, and I hope this helps, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)