Is a manifold cleaning worth it on a 617?
 

Like the title says, there's plenty of posts on how to clean a W123 manifold, but, does it make a diffrence?

My turbo 617 has over 300K miles on it, and I disabled the EGR when I purchased it about 25k miles ago. I'm sure there's plenty of gunk in there.

Thanks!

Going to depend on how much gunk is in there. If it runs strong then probably not worth it. I did see one that was very restricted years ago.

Good luck!!!

Thanks, it runs strong but has a roughness at idle that I can't solve. I've done all the usual mainentance, but ir runs rougher especially if I haven't driven it hard for a few weeks.

I wouldn't expect a sooted intake to vary in whatever symptom it creates. If anything I'd expect it to continually worsen.

If running it hard clears it and then it returns I'd think it to be injector related or sticky piston rings.

The EGR valve can get gunked up and never quite close, give that a look as it's an easy if filthy fix .

"... runs strong but has a roughness at idle"

A restricted intake wouldn't hurt idle quality since that is the lowest airflow. It would only restrict max airflow, so would reduce max horsepower. If gasoline engine are a guide, some strive for smaller carburetor bores at low power, being extreme in the "spreadbore" Quadrajet and Thermoquad carburetors. I put an aftermarket Offenhauser "Dual Port" intake on my Chrysler 383 engine. It has 2 runners to each cylinder, a smaller one off the small primary carburetor bores. The advantage of smaller bores and intake in a gasoline engine is more swirl and better atomization, which isn't very relevant in a diesel engine, as far as I know, since the combustion mechanism is much different than in a diesel (premixed vs diffusion flame).

That's a good point, thanks much!

It improves throttle response , the more miles on it I vote yes . 500k 300cd turbo of mine responded well too the service 3 years ago . Just did a valve adjustment last week on her All the hoarded 300cd parts are being applied ., 2 doors replaced with working window regulators , plus . Replaced rear seat , plus . . I’m so glad to still have this car , a touchstone amongst the better shape cars .

Thank you. The cd has better response you say? Any other diffrences?

It’s the one car out of the dailies I’ve kept that I felt it’s got the miles , let’s see what it does ,a look at how it would respond . It worked well , the one thing I would do differently would be invest the dollars to let someone else get all the carbon out of the intake , it was a gooey caked on mess . If you can set it in a container or some company that cleans parts , Febi had the kit , hopefully they still do because I’m ready to do my fleet , then other service then retire with not a care for another car for the rest of my years .

After going through the effort and mess involved cleaning out the intake, make sure to disable the EGR and add a auxiliary oil catch can to the PCV system. May as well make sure not to have to ever do it again.

Accumulated Carbon
 

Once you clean the intake and disable the E.G.R. valve the PCV system should take care of things un less your engine has problems .

Don't forget that every so often it's a good thing to run the engine hard at speed for more than 30 minutes to clear out the accumulated carbon ~ the last time I did this was on a hot day going over a steep inline called 'The Grapevine'

I wound the car up to a good cruising speed, A/C on MAX and went up the hill, near the top it nailed loudly and blew a big cloud of blue smoke then began to run better and idle smoother to boot .

This doesn't mean run it until the valves float, it means load the engine then run it hard and the caked up carbon will get hotter and hotter until it ignites and blows out .

You did this in your 240D?

What speed were you going, like 30mph??

If I hit the grapevine at say, 70mph, with a good current, I'll crest it around 52 mph. 4th gear the whole way. If someone's in the wrong lane, I'm in 3rd.
Couldn't imagine doing this with the AC running.

The 'Italian Tune Up'
 

Amazingly enough I was going north of 65 MPH in fourth gear .

That's impressive in a 240! I'm just down in San Diego, perhaps I should come up to the grapevine soon! Or head to Victorville where there's a nice, large, fast hill.