300D Compression Test

Let’s do a compression test on the om617 and see if it is still a healthy engine after 34 years.

[@bokosdieselgarage]

According to my MB service manual for the OM617 normal range is 348-435 psi (24-30 bar), minimum compression is 217 psi (15 bar) and permissible difference is max 43 psi (3 bar). It also says to test at operating temp of 80c but I’m not sure how much of a difference that makes. Improperly adjusted valves however can make a huge difference so it’s always recommended to do a valve adjustment first. Hope that helps some people.

[@mjmcomputers]

Thanks, good info to have.

[@daveyvane9431]

1983 300SD...385, 370, 340, 385, 355.

[@andrewg.1127]

This should have about 1800 more likes. Told me everything I needed to know

[@mjmcomputers]

Thanks!

[@vintage76vipergreenBeetle]

You didn't use the adapter sleeve & copper washer like it shows on, the HF diesel manual from the compression tester. I wonder if the numbers would have been higher?

[@k.j.g.9601]

Great job very helpful as usual. Will you be doing a Valve adjustment video?

[@k.j.g.9601]

Whoops, just saw you already did one. How is your Hvac system doing since you changed the relay?

[@mjmcomputers]

I'll do another valve adjustment since it is close to time. HVAC is doing well.

[@redwire2364]

That’s a pretty strong engine! How many miles does it have on it and do you know if it was rebuilt?

[@mjmcomputers]

I doubt it’s been rebuilt. I can only guess at the mileage since the odometer was broken but guessing from looking at the mileage on the carfax report and seeing when the odometer stopped working I estimate under 250k.

[@ericcastillo592]

Great videos post more fixing videos on 300sd

[@thedillestpickle]

My compression was nearly identical to yours. Lowest was around 298, highest around 320. Not too bad. I've been trying to find the cause of the misfire that happens right after the engine is started. It seems like the first 10 seconds or so the engine sounds and runs great and then it starts missing, every couple rotations, for about 3 minutes until it warms up. Puffs out white smoke during that time too. So I just had the injectors out to test them... Not sure what to think now, because they all popped at exactly 2000psi, but if I held at 1900 they would squirt, which is supposed to be bad? But they all acted the same way. Timing chain is right at 2 degrees so that's good too.

[@mjmcomputers]

Maybe a bad glow plug?

[@thedillestpickle]

@@mjmcomputers I swapped all those out for brand new bosch. The old ones actually looked decent and tested good too so I'm keeping them. So it wasn't the plugs. I've been leaning more towards fuel delivery, possibly air bubbles in the injector lines due to a leak? There is visible diesel accumulating up near the injector on cylinder 1.

[@saks_afridi]

I’m at 192 on two of my cylinders. The rest are over 200. I don’t have starting issues. What do you recommend on the two cylinders?

[@mjmcomputers]

Adjust the valves if they haven’t been done recently and just drive it.

[@adventurousairman]

I thought the recommended was 15,000, I would do it again after the valve adjustment

[@mjmcomputers]

I'll check it again after but doubt it makes much of a difference but who knows?

[@micahrlusk]

what were those things shooting out of the injector holes? looked like o-rings...

[@mjmcomputers]

Heat shields, they seal the injector to the pre chamber.

[@micahrlusk]

@@mjmcomputers oh right, now i remember. kinda fun watching them shoot out like that haha

[@gearjammer5533]

Looking to buy a 77 240D . Seller had compression done and reads 265, 265, 285, 265. (Cold test with 178,000 miles) Should I walk and where is the Good range, Cautionary range, and the Bad"Walk" range? Thanks

[@mjmcomputers]

Seems a little low but may come up some with a valve adjustment

[@gearjammer5533]

@@mjmcomputers Already did valve adjust prior to reading. Below is what I found online, but not sure the source (240D)-------- Spec. (new): 425psi, min spec 280psi, max difference between cylinders 45psi.) Mercedes recommended 425-380 Excellent. 380-330 Very Good 330-280 Good Think I'll walk

[@adventurousairman]

Just drive it ;-)

[@mjmcomputers]

Yeah, I'm missing driving it while I'm waiting for the injectors.