I had a compression test done on my 81 300SD (OM617), and the results were...
cyl. 1-300
cyl. 2-280
cyl. 3-300
cyl. 4-300
cyl. 5-280

I know 300 is what the compression is supposed to be on these engines, but what about 280? It's close, but low. Is it good, bad?
-Joe

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

These are good numbers. The bogie is all cylinders within 10% of each other. You are well within that and this is good high compression for these old engines.

The guts are in good shape.

Have a great day,

Those numbers look nice h-town.

I know 250ish is the service limit but how low can the motor actually start/run on?

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

Depends on starter, battery, ambient temp, glow plugs, and operator patience. A diesel can get pretty darn worn out and still be usable if all of the above are in your favor.

My last VW turbo diesel had about 475K on it I guess when I retired it, oil pressure at ide was 12psi hot, it fired and started running roughly for a bit in 30 degree weather, but below that, no way, not with fairly old glow plugs. Just before pulling it out I drove a 1500 mile trip strait, got 38mpg running 75mph and used 1 1/2 quarts of rotella. Apon pulling the head, the valve guides were so worn you could litteraly shimmy the valve stem around one direction almost a quarter of an inch. When for filled it with oil if you did not pour slowly, apon startup you'd get a nasty gluck gluck gluck sound and heavy oil smoke for a few moments. That motor would have lasted a lot longer if I'd had it since new, first 150K miles of neglected maintanance killed it's longevity.

You'd be amazed how far a diesel will go if you ever get it running.
The injection pump and turbo off that motor are right back in service on a 1.9L TD, the pump checked out fine at a Bosch shop and the turbo had new seals. That's it.

I love diesels...

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

Wow, I didn't realize the new 1.9L TDIs have the same pump as that. I'm actually looking into getting a 00-03 Jetta TDI here pretty soon (I believe the 04 has a different fuel setup), a LOT better fuel mileage than a CTD (Cummins Turbo Diesel)! I can't even phathom getting over 50mpg! They probably aren't the same turbo though in the A4 as during those years it is electronically controlled, as long as the motor isn't driven to softly or the turbo allowed to surge it still sounds pretty reliable.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

This series of posts helps to prove my point that compression tests are damn near useless on these engines. First, many people get numbers all over the place with the same engine. Then, everybody scratches their heads (or other body parts) after they get the numbers. They don't know what to do with them.

What matters is cold starting. Low compression can be offset somewhat by having a good battery, a good 300D starter (even in the 240ds), using synthetic oil to keep the oil thin in low temps, and having a good glow plug system. Those things are a lot cheaper than overhauling the engine.

Let's forget compression testing, and use the other, more reliable troubleshooting techniques available to us.

240Joe

The TDI's use electrically controlled pumps, they are not the same as the old engines.

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Brian Toscano

Unfourtunantly(to me) this is true. The 1.9 I refered to is the canadian only version of the old 1.6 IDI motor. More displacement and a few odd and end revisions over the 1.6. It was never sold in the U.S. Heck of a lot more power than the 1.6, the non turbo 1.9 is about as strong as the 1.6 turbo, and the 1.9 turbo is even better(but not TDI level power). Father (over) paid about $2500 for it from Overland.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

While I'm still quite curious as to how the 1.9L A4s will handle the ULSD (ultra low sulfur diesel) in the upcoming years, I haven't heard much bad about their IPs.

Are there any MBs which can attain a consistent 45+mpg like the TDIs can? I hear the new CDI will be over 40mpg but....

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

Only the 190D's as far as I know, and while more powerful and heavier, there not quite in VW diesel MPG teritory, or price for that matter. The newer CDI stuff is just flat out amazing, but they also have six miles of wire and computers, not much of a comparison really.

Jury is out on the IDI 1.9 for me, time will tell. I'm pretty content with a 1.6na to be honest, long as it's running well and geared right. It's that 240D mentality..

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

If as you say "compression is usless" what is your answer.
Or is your answer 300d starter,good battery, good glow plug system. And that fixes it?
How will this tell you the rings or valves are wore out?
Maybe I missed the point. Please explain.
Thank you.
Charlie

I think part of the point is that worn, worn out, and useless junk steel are completly different things. Where as there is either right or wrong going by the book. See my account of my last 1.6TD VW, it was worn, posibly worn out, but it still served as daily transportatin just peachy up till the day it was pulled out, including it's last thousand+ mile non stop trip at a solid 3800rpm.
If it had slightly sub par starter, battery or glow plugs, then it might have crossed into the useless junk steel catagory.

I do still like compressoin tests, it's not hard to fix valve related problems, but there's more to it than "well the compressoin is low, junk it".

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

My point is that compression testing has some serious shortcomings. First, it's very difficult to get reliable numbers. There are lots of things that can move the numbers around.

Secondly, even after you think you have a good set of numbers, you don't know what do to with them. Say for example you get a cylinder that looks low. Do you really want to tear it apart to overhaul it? Probably not.

So in the end, you work on the things that are much cheaper, and easier, to do because they might make the low compression problem much less of a real problem. A good fast starter, good glow plugs, synthetic oil, and good battery can make a car with borderline compression meet your transportation needs for years.

240Joe

[QUOTE]Originally posted by 240Joe
[B]My point is that compression testing has some serious shortcomings. First, it's very difficult to get reliable numbers.

It is not difficult to get reliable numbers. That's what the gauge is for, eh?

If a mechanic finds a low cylinder he will then do a cylinder leakage test to see where the air is going; i.e., leaking through a valve, past the piston rings, or a cracked head or bad head gasket.

It's called diagnosis. It finds a problem area.

Then we fix it. It's called engine repair.

Get it?

No, I don't get it. Please explain how you can get compression readings without a guage. I'm curious.

How many times have you seen a valve problem with our engines?

How much time and $ will it cost to repair that cylinder with low compression?

How much to just buy another car?


240Joe