First, what causes white smoke? White smoke can be unburnt fuel, oil or steam.
To start your diagnoses carefully smell the exhaust. If it smells strongly of Diesel fuel, see part 1 below. If it has a rancid bad smell see part 2. If it smells sweet or spicy it is water/antifreeze mix, see part 3.
Commonality of problem only applies to common fuel tank or filling of each tank from same supply tank.
Part 1.
Unburnt Fuel:
Unburnt fuel is caused by too low a combustion chamber temperature, low cetane rating, wrong fuel air ratio or contaminated fuel that cannot burn completely. Unburnt aerosols will cause respiratory distress and burning eyes.
Both engines affected.
Very low cetane rating of the fuel causing it not to burn completely. Engine will be hard to start.
Heavily contaminated fuel. Not likely but a number of foreign chemicals can cause white smoke. Visible soon after fill up.
Single engine affected.
On cold starts the combustion chamber is not hot enough to allow all the fuel to burn (quenching) and unburnt fuel will issue from the exhaust. Strong smell of diesel. Caused by too slow a crank speed, bad glow plugs (if fitted), fuel starvation caused by clogged filter possibly by fuel gelling at excessively low temperatures. This is almost certainly not what's happening as a running engine will be hot enough to prevent this.
Dirty injectors causing excessively lean mixture that is unable to burn as the fuel/air ratios drops below ignition point. Unburnt fuel issues from exhaust. Engine will idle rough.
Low compression in one or more cylinders.
Badly out of adjustment valves. Timing way retarded.
Bad injector pump.
Bad injector timing.
Air in fuel system.
Part 2
Single engine affected.
Burning oil. Excessive ring wear or broken piston ring(s). Oil is sucked up into cylinder and burns blue if in small quantities or white if in considerable quantity. Unlike gasoline engines Diesels will run on lubricating oil.
Holed piston crown. Oil from crankcase entering combustion chamber.
If there is a direct connection between the oil and combustion chamber the diesel can run away. The engine cannot be stopped by turning off the fuel supply as it's running on the lubricating oil. Either leave the vicinity and allow the engine to self-destruct, run out of oil, or block the air intake with a board to starve it of air. Keep hands away from the intake.
Part 3
Steam:
Both engines affected.
Excessive atmospheric humidity near or below dew point will cause steam to be seen as vapor (white).
Water in fuel. Noticeable in primary filter bowl. Drain some fuel into container and check for water.
Single engine affected.
Antifreeze mix getting into the cylinder from a cracked block, head or bad head gasket. Oil or bubbles may be visible in radiator. Lubrication oil will become whitish and thick. Rocker cover will have condensation present. Do not confuse with excessive low engine temperature operation.
Water entering air intake system. Heavy rain and or road spray can get into system and get through filter into the combustion chambers.
Kieth, your last sentence is why I put air deflectors on the coach's. You can see one in the pics of 240.
Some of the GV's have the side intake and they are ok without it as there is a big gap between vent and actuall piping for air filter container.
JohnH
Keith,
Great explanation. Very well put. I appreciate the input.
David West