I have a 1983 240d and am going to do a compression test but am wondering how to do it and what I would need to accomplish this task. any advice is helpful, Thanks.

If not done already, adjust the valves, check the timing chain stretch, and then run it hard before doing the test.

How many miles on the engine?

Do you have the tester? If not, perhaps you could rent one.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

What is the reason for doing the compression check? Are you having some sort of issue? You are doing a compression check every time you start the engine cold.

I have a tester. The engine has 201,000 miles on it. Reason for test is to know whether I can keep it or would have to sell it. and what do you mean by running it hard. sorry for the lack of technical term knowledge, I am new here.

With clean oil, get the engine up to temp, find some hills and full throttle it uphill and let it coast downhill. This helps to keep the piston rings from sticking in the grooves.

Check the timing chain for stretch and replace if needed. I've seen a few that broke.

If it starts well and has good oil pressure you should be good re: compression and crank bearings. How much oil does it consume?

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

If it runs ok then just run the car to temperature and do the rest. Don't need to check timing stretch, adjust valves or run up and down a hill unless the car has issues or you know exactly what are doing.

Compression test is more involved in diesel car than gas. You need to replace the heat shields, probably the return hoses as they will break. However you can do it from the glow plugs holes and then you have access issues with the hardlines in the way. Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

If it starts fine in the cold, and the valves are adjusted. Run it. 200k is nothing for an om61x engine. Chain stretch shouldn’t be of concern and basically non existent on a maintained 61x engine.

Here’s a simple maintenance plan to make the car run forever:
Fuel filters every 10k.
Oil change with synthetic every 5k.
Adjust the valves.
Have good glow plugs.

Drive it. ��

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Compression should be checked with the engine COLD! Not -40F cold but at ambient temperature.

It can be tested through the glow plug ports using the proper adapter eliminating the need of dealing with fuel return lines and heat shields. You need to remove the hard lines whether you test through the ports or injectors.

Valve adjustment is always a good idea. Timing chain stretch, unless extremely excessive, will have minimal effect on compression. Good idea to check since you will have the valve cover off anyway.

Timing chain stretch will affect performance and starting and would have to be extreme to be detected by a compression test.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

The factory service manual tells you to check the compressing with the engine at operating temp. However, most people check it could simply for convince.

The cheaper diesel compression tester at Harbor Freight is $60. If you go to the Harbor Freight site, you can bring up the instruction pdf and there will be a page with what engines it will work on.

If it works this will take you to the pdf.
https://manuals.harborfreight.com/manuals/58000-58999/58801-193175446800.pdf

The older kits were not Maddox kits. People did occasionally have trouble with the older kits. The little valves are Schrader valves same as they are on tire valve stems. Those have been one source of the trouble people have. The other was the 90-degree attachment was in the old kits fragile.

A few believed the gauges were not accurate and acquired other gages for their kit.

If your engine is starting OK in cold weather, you are likely getting sufficient compression. What you are looking for with the compression test is if the readings are within the allowed compression balance between cylinders. And things like you have 2 adjacent cylinders that are low, but their compressions are similar which can be a leak between the head gasket of 2 adjacent cylinders and so on.

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84 300D, 82 Volvo 244Gl Diesel

Doing a compression test to know if you should keep it or sell it is a total and complete waste of time. As I mentioned before, you are doing a compression test every time you start it cold. If it starts fine, you have good compression. If it is hard to start, then you need to make sure the valves are adjusted properly, there is not too much chain stretch, you have good filters with no air getting into the fuel system etc. After working on and owning hundreds of MB diesels over the course of 30 years, I have only checked compression on them 5-6 times if that. When I did it only confirmed what I already suspected after all of the above was done.

Random opinions.
It depends on what you find during the compression test. In the past some found that they had cylinders lower compared to the rest and were beyond the balance spec between the cylinders.

Some that found that condition instilled something inside of the cylinders to free up any positions rings that might be stuck. That worked for some but not all. For a few the compression on all cylinders went up.

However, the cylinder soak thing takes down time of a week or more.

I did not take the compression because in the past I had rebuilt the sort block on my Volvo diesel, boring out the bores to oversized pistons so I my case I knew the compression was not an issue.

However, it sat unused over a year and when I got it started, I had hazy Gary smoke at all speeds and worse on acceleration. I took a chance that it was sticking piston rings and instilled Marvel Mystery Oil into to the cylinders for one week (threw the glow plug holes), I rotated the engine and did it again and was supposed to go for another week but had to get it running after 3 days.

I cranked the engine to blow out any excess MM oil and installed the glow plugs and drove from my back yard to the driveway and did an oil change. You don't want the marvel mystery oil diluting your oil. Remember the product has a history of use on gasoline engines but not on diesels.

Took the car out on the freeway and drove it hard with some decrease in the gray haze. It took 3 more days before the haze was gone.

I did the same on the Mercedes and it had no effect at all. Apparently, I had no sticking rings.

On the Mercedes because I did a compression check I know that #5 cylinder is below the balance between cylinder specs. That was many years back.

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84 300D, 82 Volvo 244Gl Diesel

Hi guys, thanks for all the replies. I'm the dad and money guy on this project. I'm a 40-year gas hobbyist, but this is my first diesel. The concern about compression was I didn't want to put the money into all the other systems, brakes, suspension, vacuum system just to then find out we have a tired motor that is not even at the original 62hp needed to get us up and down hills.

The car starts great. 20 degrees in January after sitting a couple weeks it starts within 3-4 seconds f turning the key and almost no tail pipe smoke. But on the other hand, the YouTube valve cover cap test is not so great. at idle the blow-by is casing the oil fill cap to dance up and down, a lot. So as with gas motors I was thinking check compression to determine engine life. But sounds like the cold weather start is a reliable indicator without all the hassle? If so, next steps will be to update all fuel lines and coolant hoses, then tackle vacuum system and dead dashboard. Any other recommendations?

I was privileged enough to get some insight from a Benz mechanic who had worked on these old diesels since the 70s. He taught me a lot in my 20s when I was a young tech. He had a trick of running straight high grade non hydrated veggie oil through the fuel system bypassing the tank and would run the car for an hour or so at a time, change the oil, make sure the valves were adjusted correctly and do some hard driving and the blowby would come back virtually non existent.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

WELCOME NEWBIE ! .

Here you will find many helpful people who have done what you're doing and know how to offer good help .

Unless you, personally have adjusted the valves within 10,000 miles they're pretty much guaranteed to be out of adjustment and too tight .

If the engine starts readily at or below zero the compression is prolly fine, the valves still need periodic adjusting, once you've done them then driven a few thousand miles and re checked them they're good to go for 10,000 miles or one year .

These are dead simple cars, pretty much everything you already know is useful to keep this one running reliably and to fix all the myriad little things others tend to ignore until they sell it on .

Even the A/C isn't very hard to make work again .

Many here have pristine hobby cars, other drive their old Benz's daily, I run mine hard far and wide but I also take extremely good care of it .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

"If the engine starts readily at or below zero the compression is prolly fine, the valves still need periodic adjusting, once you've done them then driven a few thousand miles and re checked them they're good to go for 10,000 miles or one year ."
Nate,
Please explain the 'one year' part of the post you made. 10k miles sure, but If I let it sit for a year without driving there is no reason that the adjustment would be out. The F.S.M. states nothing about a time interval on that service.

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Chris
84 280sl
82 300d euro