compression question

1985 300d
Had a compression test done on a possible purchase. The car is VERY NICE.....spoke of $4,000, if compression was within 10% twixt cylinders AND within 20% of factory spec.
I did NOT get back to the test shop in time last friday, and only spoke on the phone briefly.
The test came back as follows: timing chain stretch 2 degrees...
#1=240, #2=370, #3=240, #4=335, #5=310
I DID NOT have time to discuss these numbers with the shop owner. This I will do on monday.
The car had the valves adjusted by this same shop aprox 3,500 miles ago.
MY QUESTION:
As evidenced by the great power and the 2 degree stretch, I believe that the car has been maintained with frequent oil changes etc.
WHY THE EXTREME DIFFERENCE IN CYLINDERS #1 and #3?
I do know that the car is driven by the wife for a 25 mile round trip for work daily and that they have very good records.
IS IT POSSIBLE THAT THE CAR HAS NOT REALLY BEEN DRIVEN HARD AND may have sticking rings????? Just a thought as I am wondering about this.
Other than the compression, MOST people would JUMP on the car very quickly.
I have NOT spoken with the owner yet. I believe that he is shocked at the compression development amd will be MOST disapointed as a result. He will PROBABLY play ignorant to this matter and just sell it to SOMEONE ELSE.
Please, lets hear some thoughts on this subject.
Best wishes always, and lets keep those diesels humming!
spo out

[JimSmith]

Spo123,

You did not mention mileage, or if the test was done with a hot engine or a cold one. Or if you did a wet test (I know some will caution against this but my MB dealership does them and when I asked if it was dangerous they said no, it was not) or a leakdown test. This is one of those moments when you did a test, and the results were not what you wanted, so you need to do more testing before you can know what the deal is. With some additional data you can make a better decision.

I hate to sound like an ad for Delvac 1, but I am in awe of this stuff. I put it in a 1986 190E 2.3-16 I just bought on eBay. Before changing the oil I checked the valve clearances and found all the exhaust valves slightly tight or on the edge of being tight. Then, a week or so later I did the oil change. The old oil was dino of some kind, and had been in there for less than 2,000 miles. It came out dark amber. The inside of the engine had been pretty dirty, lots of black stuff here and there, when I did the clearance checks. Anyway, after another 1,000 miles of Delvac 1, the engine was shiny clean inside but the oil was dirty looking. I mean, the engine was clean, no more black stuff or other signs of dirt. After the valve adjustment the car runs a load better too.

The point of all that is if you buy the car and want to see something will clean it up, maybe loosen a caked in ring, I would run Delvac 1 in there for a few oil changes and see what happens. Good luck, Jim

[sixto]

Might also be overdue for a valve adjustment.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[240Demon]

I would not purchase the car, at least not yet, because cylinders #1 and #3 are BELOW the lowest allowable compression allowance, of 17 Bar, or 255 psi. Depending on the mileage of the motor, this could indicate stuck rings, caked rings, or the worst, broken rings. I would have some more diagnostic work done on the car, as this may be a minor thing, or something that could get a lot worse, as it did recently in my 240D.

Thank you all for your respponses.
#1, the car HAD A VALVE ADJUSTMENT 4,000 miles ago by the COMPETANT shop that did the compression test.
#2, the car has 208,000 miles
#3, while possible that the #1 and #3 cylinders have stuck and or sticking rings..........the OTHER cylinders are excellent! ..........WAY TOO MUCH DIFFERENCE for ne!!!
#4, I am SURE that the owner is BUMMED OUT, as I have NOT heard from him all weekend, and I left ONE message at his home.
#5, I will go to the shop that did the test (THAT I PAID FOR) tomorrow and discuss the situation.
#6, I WILL NOT PURCHASE THIS CAR.
#7, What is the difference twixt a wet and a dry compression test?
#8, The test was done through the injectors.
#9, It has come to my attention that these diesels have a tendency to OVAL OUT THE CYLINDER WALLS.....any comments???
#10, I AM STILL LOOKING.
Lets keep those diesels humming!!
Spo out.

MB diesels are not prone to ovalling out their cylinder walls. As diesels typically enjoy an extended service life with good maintenance, when they are worn out, the wear will be more apparent.

The difference between a wet and dry compression test is that a small quantity of oil is inserted into the cylinder prior to the test. This helps weed out where compression losses are taking place if the dry readings are suspect.

It's good to keep looking. Impatience on my part has cost me plenty.

[leathermang]

IE, if you insert some heavy oil into a cylinder and it raises the compression numbers significantly then your rings are a problem.
If it does not help the numbers you can figure your valves are the cause of the low compression numbers.....

[gsxr]

I wouldn't refuse to buy the car based *only* on the compression test numbers, if it has great power, starts easily when cold, doesn't smoke, etc etc. There are a lot of variables that can influence compression test readings. Marshall Booth (MBCA diesel tech advisor) insists that compression tests on MB diesels are largely a waste of money, the only test needed is to see if it will start when it's really cold out (near or below freezing). Like Jim, I'm also a big believer in Mobil synthetics, and use Delvac-1 in my OM603 engines. Fantastic stuff.

Side note: Those numbers (even the "good" ones) sound low enough to where I really suspect the test was done cold, or warm, but not hot. A compression test is mostly useless unless it's done on a HOT engine, which requires working really fast (BT, DT). All the numbers should be in the 400psi range, IIRC, not low 300's. That also make me wonder if the shop was consistent on number of strokes for each cylinder - if not, the numbers are USELESS.

[leathermang]

My car may be one of those examples.. the number one cylinder was way lower than the rest... but it sure runs great...