W126, Mercedes 300sd advice

[zakthor]

I need advice about a w126 300sd my son is looking at.

My son needs a car and has been bitten by the diesel Mercedes bug. He’s been looking at the low end of the market so $4k or so. He plans to fix stuff himself which is cool I guess.

He’s planning to to go buy one tomorrow, I looked at it with him 2 days ago. I know there is deep experience here with these cars so can you give us feedback on the symptoms we noticed?

Rear shocks shot (not sls), has a tiny bit of rust at top of drivers door but otherwise rust free. E brake non-op. Ac belt disconnected.

Seat adjusters and window switches work. Seat springs are all sagging.

So, at 187k the engine sounds fantastic. Makes good power, revs easily, shuts off fast. Believe it or not it’s pretty nice to drive and ride in. Quiet and actually doesn’t feel slow. Transmission is smooth with slight clunk. Another clunk engaging reverse. Trans shifter has no detents, just jog shifter smoothly between positions - that’s not normal is it?

Engine really clean, new filters, battery. Very clean. Seller said mechanic said there’s a seal in fuel pump that isn’t holding pressure so it has a rough start if left overnight. Indeed first start was rough, 2-3 seconds of sputtering but subsequent starts were instant. I’m used to manually glowing my old truck for 10 seconds before start, this thing starts almost like a gas car.

Problem is I open the oil fill cap with engine running and there’s quite a bit of wind blowing out. Is that blow by? I’ve read the vacuum pump vents to crankcase so is that what I’m seeing? I was very surprised to see all that air escaping after hearing and driving, that cars engine sounds fantastic to me compared to other diesels and higher mileage w123/w126 that we’ve looked at.

My diesel truck once had a hole in a cylinder and blow black smoke out the crankcase vent. Insane blow by that was dirty. I can’t tell what this wind is, smells like oil not exhaust. My repaired truck engine and penta boat engine don’t puff any air out the oil fill.

Any other stuffs to test? Advice?

Of course we are telling him to buy a used Prius but it’s his money and it’s charming to see him engage. Certainly worse ways to spend $4k. Lessons to be learned.

[jhynesrockmtn]

My buddy has a habit of buying nice cars and making them nicer. For a comparison, he just sold this after owning it for a few years. 1982 240D. His brief description.

This Mercedes has been very well cared for. Original Paint (paintless dent repair can fix both dents), original interior (no cracks in dash and no rips in seats), original spare tire (unused), NO RUST. New shocks, new tires, newer CoCo Mats. A/C blows "cool" but could use a recharge of R12. 90,000 miles.



The interior looks as good as the exterior. I think he ended up getting $7k.

[zakthor]

Originally Posted by jhynesrockmtn

My buddy has a habit of buying nice cars and making them nicer. For a comparison, he just sold this after owning it for a few years. 1982 240D. His brief description.

This Mercedes has been very well cared for. Original Paint (paintless dent repair can fix both dents), original interior (no cracks in dash and no rips in seats), original spare tire (unused), NO RUST. New shocks, new tires, newer CoCo Mats. A/C blows "cool" but could use a recharge of R12. 90,000 miles.



The interior looks as good as the exterior. I think he ended up getting $7k.

Damn. I’ll show that to my son.

[Shaun @ Tru6]

Vonsmog and Speeder are the local experts on W126s here. I wouldn't mind a wagon someday but think I'd end up preferring the W124 wagon of which I have had many. Great cars and nice to see the younger gen interested in cool old cars.

[vash]

this screams PPI to me.

I know enough to screw myself..I would get a pro to peek under the hood. if I could buy a clean wagon, I would in a heartbeat. throw my kayak on the roof and go.

[Rick Lee]

Such a cool car. When I went to Germany as an exchange student in 1988, my host family picked me up from the airport in a car just like that.

[greglepore]

Peter Hedary as good as they come.

[zakthor]

Originally Posted by greglepore

Peter Hedary as good as they come.

Yeah i watched that, as did my son.Gives me hope but he didnt mention wind from vacuum pump… so i guess it really is blowby.

Car could be a piece of trash but it sure drives and sounds good, especially compared to the other ones weve driven.Its the sweetest sounding little diesel ive ever heard.

Seller inherited from original owner, has owned it for 6 months sitting next to his house.

Im kind of wary because the engine is so clean. Why a clean engine, new fuel filters and hoses but bad shocks and no ebrake?

If it was me id get a ppi, or shop longer. Live and learn i guess.

[speeder]

How long does the glow plug light stay on when you turn the key to on, (before trying to start it)? I was confused by your statement wrt glow plugs.

Some videos would be helpful from this distance, even photos would help but otherwise I have no idea on the condition of the car you are looking at. They are good cars but maintenance is beyond important. Meaning what it's had in the past as well as what you do going forward.

These old Benzes can be great to own and drive or a complete shtbox, depending on actual condition. They are widely available for cheap but bring good $$ if clean.

[speeder]

Pierre Hedary, (not Peter), makes some good videos but I don't think that he always communicates what he is trying to say clearly enough. Yes, a MB OM616/17 can have significant blow-by and still run well but blow-by is compression getting past the rings, period. It is not desirable, at all but a perfect diesel will have something like 350 psi of compression so that is a lot of pressure on the rings and with some leakage, you can still have a lot of compression left and of course it might vary on different cylinders on an old engine.

I'm about to tear-down an OM616 to find out why it's leaking so badly past the rings, it's almost the same car that Jerry posted above, a 1982 240D.

[speeder]

Originally Posted by jhynesrockmtn

My buddy has a habit of buying nice cars and making them nicer. For a comparison, he just sold this after owning it for a few years. 1982 240D. His brief description.

This Mercedes has been very well cared for. Original Paint (paintless dent repair can fix both dents), original interior (no cracks in dash and no rips in seats), original spare tire (unused), NO RUST. New shocks, new tires, newer CoCo Mats. A/C blows "cool" but could use a recharge of R12. 90,000 miles.



The interior looks as good as the exterior. I think he ended up getting $7k.

Was this a manual transmission? There is quite a difference in value between auto and stick on these, they were the only MB offered with a manual transmission in those days and the automatics can be dangerously slow. So can the manuals but not as bad.

[zakthor]

Ok my son sent a video to a local well respected extremely grumpy mercedes mechanic and he said the bottom end is toast and compression is almost certainly bad. So much for my ears.

Plenty of fish in the sea. In this case my ignorance + downside is greater than the upside. I think he should wait for jhynesrockmtn's friend to sell his next car. Hey can you lean on that guy my son is feeling impatient!

Is funny this car seemed to have so much power where the others with no blowby were relative dogs.

[speeder]

Old grumpy mechanic doesn’t know what he’s talking about. The bottom end on that engine never, and I mean never goes bad unless someone drove it on a highway with no oil in the crankcase. I literally have a pile of them that are bad motors out in the desert and I’d bet that none of them have bad crankshafts and main bearings.

If this idiot is referring to pistons and rings as the “bottom end,” you can inform him that diesel engines will not start without close to 300 psi of compression. Does it start right up or do you have to crank it forever to build up pressure before it will start? They definitely will not produce much torque with even weak compression.

This is where Pierre is correct. Some blow-by does not mean a weak engine. Post a video here of starting the engine from inside of the car, showing the glow plug light going on and then off, then crank the starter and I will give you my opinion.

Good luck!

[zakthor]

Originally Posted by speeder

Old grumpy mechanic doesn’t know what he’s talking about. The bottom end on that engine never, and I mean never goes bad unless someone drove it on a highway with no oil in the crankcase. I literally have a pile of them that are bad motors out in the desert and I’d bet that none of them have bad crankshafts and main bearings.

If this idiot is referring to pistons and rings as the “bottom end,” you can inform him that diesel engines will not start without close to 300 psi of compression. Does it start right up or do you have to crank it forever to build up pressure before it will start? They definitely will not produce much torque with even weak compression.

This is where Pierre is correct. Some blow-by does not mean a weak engine. Post a video here of starting the engine from inside of the car, showing the glow plug light going on and then off, then crank the starter and I will give you my opinion.

Good luck!

I didn’t understand the bottom end comment either. Maybe he’s hearing something like rod knock?

From cold the glows stay on 5-6 seconds, then turn key and it starts right away but engine sputters a bit for 3 seconds or so. When it’s hot engine just starts. Even starting cold the engine doesn’t smoke.

My truck with a 3.4 cylinder 3b has excellent compression and it takes a lot more glow and convincing and smoke to start and it never sounds so good.

Let me try and get him to post the videos.

[KNS]

Maybe grumpy old mechanic was trying to talk you out of it so he could buy it himself.

[zakthor]

Its a bit more than this:

https://youtube.com/shorts/1j8TqX4scp4?si=HjQx_lfDIgQAkfT6

And its better than this:

https://youtu.be/gwfJwaxaTGQ?si=mnyii6Apm59gXFQn

Also we arent getting a good vibe from seller.

[Steve Carlton]

What would the same car be worth in great condition needing nothing? What's the minimum it will cost to fix this car?

[jhynesrockmtn]

His next one is old and slow, but not a diesel. He found a very original 63 Ghia and has been going through and cleaning, making it reliable, new tires, etc. Anyone want a nice Ghia

[jhynesrockmtn]

Originally Posted by speeder

Was this a manual transmission? There is quite a difference in value between auto and stick on these, they were the only MB offered with a manual transmission in those days and the automatics can be dangerously slow. So can the manuals but not as bad.

Not a manual. Dangerously slow is about how he described it. I thought about buying it but I didn't need it, and it would be a crappy winter car in our part of the country.

[javadog]

Originally Posted by vash

this screams PPI to me.

+1

This guy is north of you. No affiliation but he knows a little bit about MB diesels.

https://mercedessource.com/

No idea if he still wrenches on cars or just works his website but a phone call is free.