According to United Diesel, causes of a non-starting diesel engine include low compression, insufficient fuel pressure, faulty glow plugs, contaminated fuel and low crank speed. Others include insufficient fuel, clogged fuel filters and internal engine problems. Many of these issues require professional evaluation with sophisticated diagnostic equipment. Others manifest clear symptoms that help vehicle owners identify the problem, even if they lack the equipment to fix it.
United Diesel explains that the color, odor and quantity of diesel engine exhaust offer valuable information about many problems. Engines that are completely non-functional do not produce any exhaust, but problems that develop gradually often affect the exhaust before the engine stops working entirely. Careful exhaust observation often reveals developing problems before they become catastrophic.
Thick, black exhaust indicates a problem in fuel quantity or quality. Common causes include clogged filters and other problems with the engine's oxygen supply. Excessive fuel in the engine also causes black exhaust.
Heavy white or light gray exhaust occurs when water or other contaminants breach the fuel tank. It also results if gasoline enters the fuel lines. Other causes of white exhaust include weak engine compression and pump timing problems caused by a dearth of fuel. According to AutoTap, burned glow plugs also turn exhaust into thick, white smoke that irritates the eyes and mucous membranes.
Diesel engines that belch blue smoke often have faulty valves and gaskets. Overloading the engine's oil reservoir also creates blue exhaust.