Blue smoke, black smoke, misfiring—don’t let these common woes get you down. Learn to diagnose your diesel engine by taking the USPS Engine Maintenance Course.
Blue smoke exhaust
A little blue smoke on start-up is normal. If it persists after the engine has warmed, the engine is burning oil and needs an overhaul.
A puff or two of black smoke on sudden acceleration is normal for an older engine, but in other engines, it indicates improper fuel combustion:
- Check the air filter or inlet for obstructions.
- Break the exhaust hose loose from the water lift muffler and check for carbon fouling in the exhaust. If more than a thin film of carbon is present, the exhaust needs cleaning (and the cylinder head and valves probably need servicing).
- If the black smoke only occurs at high engine speeds, check for overloading (a line around the propeller, a heavily fouled boat bottom, too much auxiliary equipment, etc.). If it’s a new boat, the propeller may be oversized.
A rhythmic misfiring means that one or more cylinders are misfiring. On start-up, misfiring that stops once the engine is warm suggests that one or more cylinders are losing compression, and the engine needs an overhaul.
An irregular misfiring suggests dirty fuel (check for sediment in the base of the fuel filter), water in the fuel (check for water in the filter), or plugged fuel filters—especially if the misfiring only occurs at higher engine speeds and loads. –Nigel Calder
You can learn more about maintaining your diesel or gasoline engine by taking the USPS Engine Maintenance Course at a squadron near you.