Compression Test Results, Low Pressure In One Cylinder. 1982 300TD - PeachParts Mercedes-Benz Forum

ubertino · #1 02-25-2014, 08:56 PM

I had some starting issues, replaced some glow plugs and all is well. But in the process I did a compression test through the glow plug ports, and got the following numbers:

#1 340
#2 365
#3 375
#4 370
#5 320

The #5 and #1 seem distressingly low related to the others. I'm also going through what seems a fair bit of oil, I've just started logging it when I check at fillups.

So what do these numbers tell you?

Diesel911 · #2 02-25-2014, 09:10 PM

Which one of the Vehicles, are you only using Diesel Fuel and when was the last time the Valves were adjusted?
Do you do a lot of freeway driving or City Driving?

I am losing Oil because:
I have Oil Leaks
I have smoke out of My Tail Pipe and is smells like burned Oil.
I have Piston Wrings are stuck due to carbon buildup
The little O-ring inside the Fuel Supply/Lift Pump is no good causing Oil go be sucked from inside the Fuel Injection pump and mixing with the Fuel that later burns in the Engine.
Worn Valve Guides and stems and/or worn Valve Stem seals can allow Oil to get inside of the Engine where it may be burned.

Has the Engine ever been over heated or several hours after you have run the Engine your Radiator Hoses feel hard and inflated. If it could be a indication of a head gasket or warped head problem.

ubertino · #3 02-25-2014, 10:29 PM

I forgot to add, after the compression test I had the shop do a leakdown test, and smoke came out of the oil fill cap, not the airbox or the exhaust, so it looks like it's ring related. Unless a gasket can do the same?

This car is new to me. The two previous owners took good care of the car, I have all the records for it, and this is the only thing that's really wrong with it. When I got it the thermostat needed replacing, and it ran a bit hot, but it didn't get to red.

There isn't much smoke out of the tail pipe, and it doesn't smell like burned oil.

As for the other causes, I haven't investigated yet, but I plan to.

t walgamuth · #4 02-25-2014, 10:40 PM

I think your compression test looks very good. Within 10% is very good.

whunter · #5 02-25-2014, 10:45 PM

Quote:

Originally Posted by ubertino

I had some starting issues, replaced some glow plugs and all is well. But in the process I did a compression test through the glow plug ports, and got the following numbers:

#1 340
#2 365
#3 375
#4 370
#5 320

The #5 and #1 seem distressingly low related to the others.
I'm also going through what seems a fair bit of oil, I've just started logging it when I check at fill ups.

So what do these numbers tell you?

What year, model, engine are the compression results from ???

.

jake12tech · #6 02-26-2014, 03:36 AM

You wouldn't believe what stuck rings can do - run Marvel Mystery Oil through it a few times and see what happens. It's something basic to start with and cheap at that.

aieeegrunt · #7 02-26-2014, 07:42 AM

"Run through" as in the fuel tank, or pulling the injectors/glow plugs and putting it directly in the cylinders?

ubertino · #8 02-26-2014, 09:19 AM

@whunter It's a 1982 300TD with 186k on it, the one is my signature. It's the OM617a engine.

I've heard good things about the Marvel Oil before, how do I get it into the combustion chamber?

whunter · #9 02-26-2014, 11:51 AM

Quote:

Originally Posted by ubertino

@whunter It's a 1982 300TD with 186k on it, the one is my signature. It's the OM617a engine.

I've heard good things about the Marvel Oil before, how do I get it into the combustion chamber?

Through the glow plug or injector hole.

It is easier through the injector hole.

.

crazy4diesel · #10 02-26-2014, 02:41 PM

Quote:

Originally Posted by t walgamuth

I think your compression test looks very good. Within 10% is very good.

Did I miss something? Isn't the difference from 320 to 375 (or do you not go from lowest to highest? I'm really not sure) close to 15%?

OK, good, I just wanted to make sure I was using the right numbers when doing this, Lowest and Highest number. Thanks.

BWhitmore · #11 02-26-2014, 02:56 PM

Normally when performing a compression test, it is advised to do the test on a warm engine, perform the test when all cylinders have the glow plugs or injectors removed. Given your results, plus the fact that your engine starts and runs well, I would say that you have good compression.

Maxbumpo · #12 02-26-2014, 05:09 PM

If the valves were not adjusted prior to the test, the results are very suspect.

BillGrissom · #13 02-27-2014, 01:55 AM

Do you see strong blow-by from the oil fill cover? That is a sign of leak past rings. My 82 engine has >400 psig all cyl and shows none at all. My 84 engine shows noticeable puffing w/ one cyl at 350 psig and all others >400 psig. I don't know the mileage of either engine, but appears the 82 was recently rebuilt (camshaft looks new).

If minimal blow-by, I wouldn't worry for now. As long as it starts easy on cold mornings, you are fine. My 1985 was ~250 psig in all cyl as I recall when it started needing the block heater to start when ~30 F. That was ~310K miles. The engine failed at 330K (chunks of several pistons missing).

t walgamuth · #14 02-27-2014, 02:10 AM

Quote:

Originally Posted by crazy4diesel

Did I miss something? Isn't the difference from 320 to 375 (or do you not go from lowest to highest? I'm really not sure) close to 15%?

15% is still good.

ubertino · #15 02-27-2014, 08:28 AM

According to the services records that came with the car, the valves were adjusted last October.

It starts and runs fairly easily in the cold, mind you that it's Michigan cold, right now that means 6-10 fahrenheit.

There is definitely some blowby, but it's not hemorrhaging oil out of the fill cap.

It sounds like there is some of the miracle oil in the future for me.