I was planning on doing an engine flush here soon next time I change my oil on my 240D. Don't know if the PO did or not. What's the generally accepted method/material you guys use?

__________________
- 1979 W123 240D 4-speed, 390k miles

There are some methods that folks use that IMHO are dangerous. Running an engine even for two seconds on nothing but solvent is risky.

For me, assuming you are talking about the 240D in your sig, I would do it by doing some frequent HOT, overnight oil and filter changes using one of the diesel oils such as Rotella, Delo or Delvac. These have lots of detergents for soot dispersal.

If you want to help it along, once engine is hot and you pull the drain plug get ready with a gallon of diesel fuel in a jug. Give the engine about 15 minutes so the oil mostly drains out and then pour the diesel fuel in the oil filler hole as fast as you can. Let it just flood through the dead, hot engine and then let it drain overnight before replacing filter, plug and oil.

Draining the oil while it's as hot as you can get it will bring out more of the contaminants while they are still suspended in the oil before the oil cools allowing the crud to stick to parts within. Draining overnight gets those last drops which are the sludgiest.

Hope this helps.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

The generally accepted method is to drain the oil, change the filter, and install eight quarts of synthetic oil.

That's all the "flush" that you need unless the engine has been horribly abused.

Be advised that any "flush" will definitely provide significantly lower viscosity than engine oil, thereby running the significant risk of much higher than desired wear for as long as you run the engine with the flush. If you run the engine for one minute, the flush cannot seriously do much of anything. If you run the engine for two hours, the flush will do some cleaning............and you'll be without some cylinder, ring, and camshaft material when done.

I've done a flush on a gas engine with dieselFilled it up and shook truck engine for five minutes.then drained and filled with new oil.It had a clogged screen.However do not let engine start till you build oil pressure.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

This is good advice. Do several subsequent oil changes at 200 miles or so.

Thanks! About how many times should I do this? Quite a few, or until fresh oil stops coming out black and gunky? Also, diesel will not hurt the engine as long as its given a while to drain, correct?

__________________
- 1979 W123 240D 4-speed, 390k miles

What's the difference between a flush and purge? Or, I know what a purge is, so what is a flush?

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Maybe be the same as what you're thinking. "Flush" meaning cleaning the cam and engine out of gunk and sludge without having to take things apart.

__________________
- 1979 W123 240D 4-speed, 390k miles

To the OP:

Are you asking about flushing the crankcase or the water jacket in the engine?

If you are asking about the water jacket there is an FSM procedure for this. You use citric acid powder available from m-b. Also Diesel Giant has a write up on this as well.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Normally, a diesel purge is using a cleaning agent and running it through your car's fuel system, usually at 100% concentration in a little under-hood "fuel tank" made from a plastic bottle or some such. The one you see most often is Lubro Moly's Diesel Purge. It's supposed to clean up injector nozzles, etc. There are some very good pictures below that paint the picture well:

Diesel Purge Mercedes diesel maintenance tips

An engine flush is using some kind of strong solvent or oil additive right before or at the time of oil change to try and clean the inside of the engine and it's lubrication system. Really the best way to do this is just upping the frequency of your oil changes a few times.

A coolant flush is running some water-soluble cleaning agent and the Mercedes citrus flush and then lots of clean water through your cooling system to remove oils and gunk.

Mercedes Citrus Flush

Do it enough times that the oil is no longer coming out black as night. After a few hundred miles a well-"flushed" engine should have coffee colored oil instead.

Flushing the crankcase.z

Thanks for the input, fellas!

__________________
- 1979 W123 240D 4-speed, 390k miles

Why do you want to flush the engine? Diesels generally don't sludge up as much as a gas engine. Be aware that any sludge that is sitting in crevasses and corners will come loose and likely clog the oil pickup screen. This will lead to loss of oil pressure or if a chunk of carbon gets past the screen a locked oil pump.

Left alone and changing the oil on time or say 1000 miles eariler than normal, any sludge wil stay put and not bother anything or slowly be washed away.

If you really wanted to do something, pull the oil pan and manually clean the pan and pickup as this is where most of the junk will be.

um, a diesel motor is never going to have clear or amber colored oil.
it's ALWAYS going to be ink black moments after you start the motor.

however, it should not be thick or chunky. smooth oil is good.
before you decide the motor needs some kind of flush, take the oil fill cap off, and look around the cam lobes. if you can see the casting flash on the motor parts, the oil is normal, and a simple oil change is all that's needed.
if however, you see thick sludge on the non moving parts... then yeah, at a minimum, I'd dump the oil and filter, and install fresh clean oil, then put about 3-500 miles on it, and change it again.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

USE ONLY SYNTHETIC DIESEL RATED OILS !

__________________
'84 300SD sold
124.128