I can't remember where I read this many months ago, but I know there is an effective method for cleaning the black sludge/grime from the intake-to-exhaust/turbo manifold crossover pipe. It's a squarish aluminum pipe that crosses over the valve cover. Once cleaned, the performance is a little better. I did a search just now but didn't see anything. I think someone wrote they submersed the entire pipe in either Simple Green overnight or maybe it was lacquer thinner... I don't remember. Whatever it was it really worked since the pipe looked like new.

Boston,

I did my old SDL a couple of years ago. I found - I believe - a Gunk or STP brand spray can marked "intake manifold cleaner". My intake wasn't bad, 1/8" or less all around. This stuff cleaned that out very well. I used 2 cans for the cross-over and intake.

In general, I would think there is much excess air available coming from the turbo and intake in this diesel. This is different than a gas engine that is usually air limited. It doesn't hurt to clean it but I wouldn't expect a difference unless you have a very large build up.

Chuck

I just found a bottle of Castrol purple cleaner that comes in a spray bottle. That stuff is amazing. I sprayed it on directly to the oil/gunk and it melted the grime away. No scrubbing needed, only wiped it with a paper towel. That stuff's amazing. I think it said on the bottle that it "creates an environment too slippery for oil or grease to cling to". Damn.

you can get the same stuff with a different name for half the price at Wal-Mart
it’s called Purple Power

You'd also be surprised to see what has formed around the intake valve stems after you remove the intake manifold and have a look-see. This is an area that will restrict air-flow and performance.

You can only clean in and around each valve while it is closed, don't want chunks of debris falling into the chamber.

One of the theories behind 603.97 rod bending.

Sixto
95 S420
87 300SDL