As most of you already know, a diesel engine operates under high internal pressure, and generates a fair amount of blow-by, which are combustion gases that make it past the piston rings into the crankcase. In a gasoline engine, these gases can simply be routed back into the intake and get burnt away. But because diesel intakes are pressurized instead of vacuums, you can't simply route these gases into the intake, and manufacturers up until now have simply vented them to the environment through a downward-pointing rubber hose. These combustion byproducts are very oily and if allowed to touch anything, can build up quite a thick layer of grime rapidly.
Some diesel engines have radiators on the side of the coach, so blow-by exiting mid-engine simply works toward the back, soiling the chassis and toad but not affecting the radiator much. If your coach has a rear-facing radiator however, these oily fumes can quickly build up in the radiator fins as they're sucked up and pushed through it by the fan, and reduce the radiator's efficiency greatly. Many expensive engine failures have been directly attributable to this effect.
Thus, in this circumstance you MUST route the fumes away from the radiator at least. Neither Caterpillar nor Freightliner nor Fleetwood take responsibility for this situation, so you're on your own to come up with a solution. Here's what a good solution should accomplish as a minimum:
No possibility of restriction of the blow-by airflow.
No gases released upwind of the radiator.
No grime deposited on the motorhome chassis or toad.
Solving the last constraint is trickier than simply extending the tube to the back. What we've come up with is the following:
1. A 1-1/2" I.D. thick-walled reinforced clear PVC hose slips over the end of the existing blow- by down tube (held on by a hose clamp) and gently extends toward the curb side of the open trailer hitch crosspiece. PVC Hose
2. At the lowest point in the hose (approximately midway), a 1/8" hole is drilled to form a funnel-shaped path for liquids to drip out of the tube. A plastic quart container with flat sides was drilled through with a 1-1/2" hole saw (undersized compared to the O.D. of the PVC hose) midway up the sides, and then slid over the PVC hose upside-down to cover the hole, blocking the release of gases but sequestering liquids. Sludge Container
3. A couple of 1-1/2" steel muffler sections take a 90 degree bend into the center of the hitch, continue through the hitch and then bend 45 degrees aft and slightly down, exiting just in front of and below the main exhaust. The pipes are joined with J-B Weld for a leakproof seal. Short pieces of foam pipe insulation around the pipe just inside both ends of the hitch crosspiece stop the pipe from possible rattling. ElbowTailpiece
Thus, the flow is not restricted in diameter and is self-draining. The extension cannot collapse and is protected from the exhaust heat. The gases are deflected down and away from the vehicles by the powerful main engine exhaust, keeping the coach undercarriage and the toad free from grime. Liquids remaining in the extension collect in a separate container, and these liquids can be monitored and drained at your leisure.
You'd be surprised how clean your toad can remain when that thin film of oil is not always being deposited on it, collecting dirt, in addition to not having those black smudges.
