narwhal,

I think that stuff is a product of blow-by oil vapors/droplets wetting the inside diameter of the intake manifold, and then having that relatively sticky surface exposed to exhaust particulate and smoke from the exhaust gas recirculation port. Unless you are suggesting biodiesel makes more soot I do not think using biodiesel is the problem. It is the concept of cycling exhaust through the intake, which is apparently something the engine doesn't like any more than your or I would.

Given an experience like the one Lightman has shown in the photo, and that these deposits are actually pretty common from other threads here, why is this practice still used? There must be some other way to control the formation of NOX, or what ever the EGR system controls in the emissions. Maybe if they took it off the downstream side of the catalyst in the later cars it would be hot enough to be effective, but not so full of junk!

It seems to me if the intake can plug up like that in such a short time there is a malfunction or design defect in the emissions equipment, which has a much longer warrantee than the rest of the typical car, like 100,000 miles or some such number. I would think a routine cleaning would be necessary to maintain the emissions equipment and that should be covered. Maybe if it started costing money an engineer would get the assignment to fix the problem and stop sending exhaust into the intake.

Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)