240 to Turbo 300 - PeachParts Mercedes-Benz Forum

#1 11-07-2002, 03:41 PM

Here is my continuing issue: As you all know, I have a nice 1983 240D with manual transmission, A/C is cold, everything works. Starts/stops fine, brakes fine. 144K miles, get 27 mpg. Runs fine with one big exception. Horrible smoking problem using 1 qt of oil every 450 miles. James Bond smoke screen on the onramps!! Problem could be bad valves or bad rings. Options.

1. Have a valve job done on it. (seems to smoke too much for this to be the problem)
2. Have a complete rebuild done on it.
3. Buy a rebuilt 300 Turbo engine from Metric Motors or another vendor and have it dropped in the car, the old engine goes away.
4. Buy a used 300 Turbo engine, but how can a person tell if the used engine is good?

I don't believe the vacuum diaphram is bad and sucking oil into the engine. The vacuum line goes up to the master cylinder, where does it get to the intake manifold? My 76 had a white tube running from the VP to the intake, I don't seem to have that on this 83.

I like the car but it doesn't seem to be cooperating with me to have a mutually beneficial relationship!

What do you think?

leathermang · #2 11-07-2002, 03:58 PM

You don't THINK the vacuum is leaking ? What does that mean... go check it ... then do a compression test... and if it is not the rings consider putting new valve seals on it... THEN start thinking about those other deals... you pretty much have the perfect car sans the oil... so if you can correct that specifically I sure suggest driving as long as you can before the other options are tackled...just my opinion...

#3 11-07-2002, 04:00 PM

I think you're putting the cart in front of the horse. Before getting pessimistic about the engine you need to go through the basics.

Begin with a compression test. If the compression is bad, do a leak down test and listen for where the hiss is coming from. If it's not coming from the oil filler, then you can probably get by with a valve job.

If the compression is good, check the injection pump timing and the injectors for a uniform spray pattern.

By going through these basics, you will then have a much better idea where you're at.

Good luck,

#4 11-07-2002, 05:43 PM

In an effort to be brief, I didn't put all the facts in. Here is more information. All performed since April 2002.

compression is 400, 400, 400, 380
valves adjusted. Timing chain & tensioner replaced
Valve Seals replaced $425. August 13th, NO change in oil use

Unfortunately I just have basic tools with little space or expretise to do major repairs. I just love the cars. I have checked the vacuum lines (car holds the door locks for about 2-3 days) but am not aware if there is another vacuum line other than the one from the VP to the master cylinder that I could check. On an 83, where is the vacuum line to the intake to see if oil is being sucked in and not valves or rings? I pulled the V lines apart (between VP and Master cylinder) and don't see any oil residure. How can the VP pull oil into the engine on this car if vacuum lines aren't connected to the crankcase and intake?

Forgive my lack of knowledge, but how would the injection pump and or spray pattern cause such a high oil burn rate like I have?

Should I have another compression test done? I read on a few of the threads that an engine with good compression could still have bad rings because the oil seals the cylinder. Of course if the oil was sealing the rings, the test results would be the same. So what is a good way of testing if the valves and/or rings are bad?

I like the car but not knowing what is causing the oil burn rate is very frustrating! People driving behind me hate me I'm sure!! I would just as soon solve the problem as inexpensively as possible (rebuilt engines I believe are a few $$$). Thanks for your help.

leathermang · #5 11-07-2002, 06:10 PM

I am the only person in the world using more oil than you... but the funny thing is that if you did not know that fact you would think my engine is in great condition.... If I just drive past you you would think I was burning NO oil...
Even funnier is that the oil burning situation SURVIVED an engine rebuild (according to the PO.)...
My car is also a 240 with manual trans... If you did decide to go with a 300 engine... I would suggest the non turbo in order to keep some of your nice engine working area available...
I hope you figure out what is happening.... maybe it will enlighten the situation with mine...

If your injection system were very far off you would not be getting such nice mileage... fuel being off/ not burning does cause smoke... but not oil burning....

You are visualizing the VP and oil burning backwards... the line from the VP to the center of the air cleaner will allow oil to be taken in and burned by the engine if the diaphram is broken... If you take the air cleaner top off and you have OIL on the INSIDE of the paper element then you have a busted diaphram on the VP...

psfred · #6 11-07-2002, 07:28 PM

With the compression you have (like new, for all intents and purposes, 300 is the wear limit), your valves and rings are fine.

Oil burning is almost certainly valve stems/valve stem seals or vac pump, most likely vac pump.

Heavy smoke at full throttle, with injection timing correct, is either a stuck injection timer or stretched timing chain.

I'd check the chain -- if worn, replace, then reset injection timing. Black smoke should go away. If not (and you may want to check anyway), reduce the max fuel delivery on the pump. Lots of people try to get more power by turning up the max fuel delivery, getting instead more smoke a full throttle. Also known as the altitude adjuster.... or ALDA.

Peter

#7 11-07-2002, 09:19 PM

The timing chain and tensioner were replaced in April 2002 and valve seals were replaced in August 2002.

This is where I part stories with my mechanic, I contend the seals were never replaced (no evidence of valve cover being taken off). I burn as much oil now - 1qt per 450 miles - as before the supposed replacement of the seals. I really think they just forgot to get to my car, the front office called, said it was done since it was in the computer to have this work done. Bottom line I don't think the seals were replaced.

If it was valve stems, wouldn't that call for a valve job since the guides would need to be replaced?

On the VP, I don't have any oil in the air cleaner housing or on the filter. There is not a vacuum hose attached to the air filter housing at all, so where is the vacuum hose to the intake?

I do have lots of smoke, but I'm sure most of it is oil (still get 27 mpg). I will have the IP timing checked though.

Thanks for your help.

psfred · #8 11-07-2002, 11:08 PM

Should be easy to find the vent line from the vac pump -- pump is directly in front of the injection pump and there are two hoses -- one is the main vac line to the booster and the other is the vent line. Goes to the air filter housing or the intake manifold, usually "clear" white plastic, no longer very clear. Any oil in there means the vac pump diaphram is shot.

You can get a quart of oil down the valve guide seals in 450 miles, but if they are leaking that much you will have a big puff of blue smoke on startup cold. May also get a puff of blue smoke when you take off from extended (more than a minute or two) idle.

Don't forget to look for leaks on the oil cooler lines or drips off the bottom of the engine somewhere. Doesn't take all that long at a drip a minute to loose a quart of oil!

Peter

leathermang · #9 11-07-2002, 11:15 PM

That is a possibility,,, it could also be possible that they installed them without using the protective shield and messed up the sealing surface...I bought a set which did not come with them.. but my second set did have them....
No, the valve stem bushings do not necessarily need to be replace just because the valve stem seals need replacing....they are just rubber... so have a shorter life than the valve stem bushings....

psfred · #10 11-07-2002, 11:25 PM

With good compression, new chain, and good timing, the black smoke a full throttle almost has to be a stuck timer (unlikely) or overfueling. I don't know where the adjustment is, but a Bosch service center will -- find out, unlock it, and turn the screw 1/8 turn at a time leaner until the smoke stops.

If you have an aluminum "square can" on top of or attached to the rear of the IP, remove the anti-tamper cover (black plastic and a thin metal tube), unlock the screw, and follow the directions in a number of other posts for adjusting the ALDA -- works the same way as for a turbo, just senses ambient air pressure. I don't know what type of altitude compensater at 240 has.

Peter

#11 11-08-2002, 10:18 AM

My 76 had the "white" vacuum line to the intake but this 83 does not. The only line I see coming out of the VP is the one going to the booster. If it wasn't raining so much I would get under the car to check for vacuum lines to the bottom of the intake. Are we sure the 83's have vacuum lines to the intake?

I don't have any drops of oil in the driveway (my wife wouldn't let me park there if there was). I'm not losing the oil by drips, it is definately burning.

I get most of the smoke on acceleration but even at idle you can see smoke hitting off the ground from the exhaust, but HUGE amounts of smoke on acceleration. Smoke is grayish with just a hint of blue.

I am not very knowledgable about the valve system components so... The head doesn't have to come off to replace the valve stem bushings? The bushings and seals (with protective cover) are not the same item? If valve stems were bad is that the same thing as bushings or seals or is that different? Are guides the same as bushings? Can stems get worn and thus need to have the valves replaced? Thanks!

psfred · #12 11-08-2002, 07:27 PM

The only way you could use that much oil and not leak it is through the vac pump or down the valve guides.

Valve guides are the steel (intake) and bronze (exhaust) tubes that the valves go up and down in. There are also rubber seals at the top of the guide to limit the amount of oil that goes down --- oil pours on top from the camshaft, and SOME oil is required (or the valves would sieze in the guides!). If the guides are oversize or worn, or the seals bad or damaged during installation, oil gets sucked down.

Vac pump must vent somewhere, and I though all the 615 engines had a vent line to the intake or air filter housing, but I will check.

Head must come off to fix guides, doesn't for seals.

Peter

#13 11-09-2002, 01:23 AM

That's what I thought about replacing guides, the head must come off. Since it is off, a complete valve job might as well be done. That means a few $$ since I can't do it myself. Then I wonder if I do the valve job, maybe the rings are bad also or instead of the valves, then a ring job would be required, as you know now we're talking more money than I bought the car for! This oil burning is so puzzling to me!

I looked again at the VP, there is 1 line going out (or in depending on your point of view) and runs to the master cylinder on the firewall. There are a couple of small plastic lines as offshoots but I don't see any getting near the intake manifold or air cleaner. Another puzzle!

Tim

psfred · #14 11-09-2002, 10:22 AM

Tim:

If you have 400 psi compression, there is nothing wrong with your valves or pistons or rings, this is nearly new condition. You have oil going down the engine somewhere, not blowby from leaking rings or low compression from worn valves.

That VP has to vent somewhere, but I don't have much info at the moment on the 83 -- I've got the engine manual, and will look, but it must be different that the ealier ones.

Check the oil return pipe and the oil separator, if you have one, in the air filter housing. If the pipe is plugged of the separator leaking, you may be dumping oil down the intake rather than returning it to the pan, but I cannot believe an engine with that compression that good is blowing enough oil to see your consumption.

Peter

#15 11-10-2002, 02:03 AM

I'm interested in what the manual has to say on the VP and oil to the intake, let me know.

The oil separator or return pipe are a possibility I haven't thought of. I'll let you know on this. Maybe the compression test was not accurate, but it was done by a Indie with a very good rep. As I said, it's a puzzle!!

Tim