Blowng smoke, low compression, but goes like stink???? - PeachParts Mercedes-Benz Forum

jassz · #1 03-30-2003, 07:09 PM

Ooooo, my heart is all a flutter. We searched for months for a 300TD wagon, and managed to finally find a fairly nice one last week. But, it wasn't perfect and we were mentally tallying the cost of the parts we would need (self leveling strut being the most expensive). Anyhoo.... I actually managed to find a parts car today!! Exactly the same year (1981), with considerably more rust, but much lower milage (only 136,000 miles). I was sure something must have happened to it (ran out of oil, over heated or something) for the motor to be shot at that low mileage, but the guy did not know what happened. It started blowing smoke, would not pass emission testing (but did the previous year), so the guy had compression testing done and was told one cylinder was shot (I don't have the readings, but I may call him back to ask him). We decided that it was more than worth the price (about $700 US) just in parts we need (transmission and struts alone). We weren't really expecting much in terms of power, but this thing goes LIKE STINK. I have only driven three diesels so far, and this is by far the most powerful. How can that be??

I expected it to barely start, but it starts no problem.

Any suggestions as to the cause of the low compression, given the amount of power it still has? My husband is all gung-ho to rebuild the motor, and put it in our car, which has a better chassis. He's not a mechanic, but definitely mechanically inclined. Looks like his weekends are set for the next few year(s).

JimSmith · #2 03-30-2003, 11:48 PM

jassz,

I would have the test repeated and then you can post the results. I know there are some that find doing a wet test after the dry test to distinguish whether the problem is with the valves or the cylinder to piston ring seal is dangerous, but my dealership does this on Diesels (especially 350SD and SDL models coming in with oil consumption problems) regularly. I would also look into a leak down test to further isolate the problem.

To get a quick idea, take the oil cap off the valve cover while the engine is running, and note if you get a huge puffing cloud of smoke or not. Some blowby is normal, and a lot of blowby is a sign of deterioration. If the amount of blowby coming out affects your feel or ability to get the cap back on, there is probably something wrong.

Also, what do the valve clearances look like? When was the last time they were adjusted?

If the car runs as well you say it does, then I would suspect the data. There are a number of cases reported here where an individual with too little familiarity with their Diesel sold it as junk when there was relatively little wrong with it.

Good luck, Jim

#3 03-31-2003, 03:31 AM

He never told me, but I highly suspect the previous owner of my car sold it to me because he thought the engine and/or transmission was dying. The shop that did the front seal on the transmission left the bowden cable off, causing the car to be slower than a slug and barely shift.. that was two years and nearly 90,000 miles ago.. his loss.

Jim is right, it does happen.. it's very possible that engine is in better shape than your current one.. get the compression checked again and post the numbers.

gsxr · #4 03-31-2003, 02:57 PM

Hi Natalie,

It's not likely to have low compression and run that good. I agree with Jim. Here's my theories:

1- They did a cold compression test and the numbers were below spec. Well, DUH! the test has to be done with a HOT engine to be meaningful. For some reason a lot of "mechanics" seem to forget this little technicality.

2- If the valves are out of adjustment it can make compression numbers low on the affected cylinders. These engines need adjustment every 15kmi, and rarely do people actually have this done. Adjust the valves BEFORE doing a hot compression test. The car may have had one cylinder with a tight valve that skewed the original test results, leading the previous owner to think the engine was shot.

Either way, I bet there is NOTHING seriously wrong with engine. Do an Italian tune-up on it and you may want to swap that engine into your other car - no rebuild required!

On a side note, you might want to check out the MBZ.org diesel email list... you will get a lot of responses over there as well, as not many people frequent this forum AND that list. The owner happens to be North of the Border as well (forget where except it's cold there).

The sign-up form is here:

http://diesel.list.mbz.org/

Best regards,

jassz · #5 03-31-2003, 10:19 PM

I'm not sure how much you can tell from these pictures, but we're trying to determine how much blow by is too much. THere is definitely some. I was going to try to get a short video clip, but the cassette has jammed in the camera.

Now I need to find a digital camera repair board.

The smoking out of the tailpipe definitely gets better as the car warms up.

gsxr, I'm sure that diesel list is great, but 50-100 emails per day would be too much for me! I spend too much time on the computer as it is!

jassz · #6 03-31-2003, 10:19 PM

And the tailpipe...

jassz · #7 03-31-2003, 10:20 PM

Ooops! Can I remove that last post??

gsxr · #8 03-31-2003, 10:33 PM

Don't worry about the blowby from the crankcase, that's pretty much normal. I bet your other engines do the same thing. (?) Hard to tell on the exhaust but the more important item is how much smoke it blows under load, IMO. Blue smoke at idle could mean valve seals or bad rings, but with good power the rings are likely OK.

About the MBZ list, get the digest version. I get 1-5 digests per day, and the subject lines are all at the top so you can just skim the subjects... if there's nothing that interests you, delete without reading. I'd say 2/3 of the content doesn't interest me but the other 1/3 is invaluable! Plus it's free to subscribe AND unsubscribe...

Regards,

coachgeo · #9 03-31-2003, 11:28 PM

Quote:

Originally posted by gsxr
...About the MBZ list, ...

Regards,

Please lets push for bullitin board participation and not send folk over to a mail list.

Let's get the mail list guru's onto this board. The dialog is so much easier on a bullitin board. It's just no comparison. A mail list format is such a waste. I get the list digest and 99.9% of the time I just can it with out looking at it. Finding the one or two interesting messages, even though u know by the list of titles about where the message is "supose" to be.. its still a pain to find it amongst all the messages. Also mail list archives are just about worthless to search.

Bullitin Boards are hands down superior to mail list and safer virus wise so come on.. if your on a mail list..... encourage the guru's of the list to join in here and find out how much better things are on the bulletin board side.

(in the voice of Obewon Kanobe (sp?)) LUKE... may the BOARD be with you

gsxr · #10 04-01-2003, 12:57 AM

Actually I prefer to use both. I think the quality of the email list to be slightly higher, IMO, at least some of the time. But this forum is great too. I used to post on mbnz.org back before they folded and got sucked into benzworld, or whatever it was, with that hideous threaded format (I haven't been therein months).

My only gripe here is that there is an awful lot of misinformation spread on this forum which I find highly irritating. For example that nut who claims to be an MB tech for 30 years screaming that synthetic oil will blow up your engine, steal your wife, and shoot your dog. Whatever. That stuff isn't tolerated on the email list. The Mercedesshop forum does have a much wider range of topics, particularly performance oriented stuff, which is aweseom. At MBZ.org only the diesel list (AFAICT) has major traffic. Most of the others are pretty quiet. But fair is fair, and I push this forum to the email list as well!

Regards,

jhal · #11 04-01-2003, 09:10 AM

Jassz, I can't tell completly from your engine picture, but it appears that you don't have an elbow fitting on your pcv hose. It looks like it may be kinked. If so, it can cause excessive crankcase pressures in your engine, causing all kinds of unpleasent side effects.

Wallknight · #12 04-01-2003, 01:34 PM

OOH! good call jhal! That could be a problem. Looks like the original broke, the owner couldnt find an elbow, so he used an old heater hose. I know. I did the same for a while!!

jassz - email Phil at partshop- he'll be able to get one to you for a few $$.

jassz · #13 04-01-2003, 11:12 PM

First of all, I just wanted to say how VERY helpful this board is! Amazing!

Thanks for the tip on the elbow fitting. What is there doesn't really look kinked, but maybe air is not flowing as it should be.

gsxr, as far as comparing blowby... I don't have too much to compare too. Celeste (a diesel conversion) had a rebuilt motor and several mechanics commented on how very little blowby there was. Belinda (my current 300td) has about teh same as this parts car (it's white smoke... is that relevant?). We had a mechanical inspection with someone who is supposedly an expert in these types of cars, and no comment was made about it being excessive. But, the parts car has way more smoke coming out the tail pipe (kinda white, kinda blue smoke). Does that sound like valves? It is definitely idling very rough, but it does get a bit better as it warms up. There is no oil running up the dipstick, and no smoke from the dipstick tube.

We phoned the previous owner to ask him for the compression readings. He is going to call his mechanic and get back to us tomorrow. He did say that the smoking out the tailpipe was an 'all of the sudden thing' , not a gradual deterioration. Any thoughts on that? Prior to us buying the car he told us the car had a lot of blowby (according to his mechanic). Tonight when we talked to him, he said that the mechanic based this comment on the fact that there is oil in the airfilter housing.

Isn't there always some oil in the air filter housing? That's why there's a drain line back to the oil pan?

We're also working on the video camera, so we may be able to post a short clip.

Natalie

#14 04-01-2003, 11:25 PM

Quote:

Originally posted by jassz
First of all, I just wanted to say how VERY helpful this board is! Amazing!

I am glad to hear that you are getting lots of help from this board. Most of around here are friendly and are glad to answer all your questions. I am sure that you are finding it much more helpful and friendly than MBCanda.com

I also noticed that you live in B.C., so you might want to check out the thread for a North West Get Together a few of us are planning. Here is the link: http://www.peachparts.com/shopforum/showthread.php?threadid=60782

JimSmith · #15 04-01-2003, 11:41 PM

jassz,

I did not mean to start a long discussion on quantifying blow by. If an engine is in factory new condition, there is relatively little blow by. If it is getting on in years and miles but is still in good health, there will be noticable blow by. Enough that if the air cleaner is not wiped out now and then, that it will be apparent there. If there is so much blow by that you have to concentrate for a second while you put the cap back on, and you can feel and hear pulsations in the stream of gasses coming out the oil fill openning, the engine is getting tired. I did not think your photo showed excessive or abnormal blow by, but getting a more reasonable view of the condition requires one to be there to see and hear what is going on.

I would have the compression test repeated, and I would do it wet as well as dry if the numbers are low.

I thought your exhaust photo showed more than normal smoking so you do have something going on. I am not sure of your vacuum pump type, but I have had the diaphragm fail with spectacular results, especially at idle, in a 220D. A smaller leak there made some pretty good blue and white smoke on my 240D. These cars had the vacuum pump exhaust feed into the intake through a translucent white plastic material hose or tube. If your engine has such an arrangement, and the diaphragm is leaking the hose/tube will be black from oil in the inside. Which, due to the translucent nature of the tube is visible from the outside. There are a number of other possibilites too, but I think we need some additional data, like the compression numbers to help figure this situation out.

Good luck, Jim