ENGINE AR-COMPLETE 2869798 - Caterpillar

engine operation at no load or lightly loaded conditions (less than 15% load) may result in exhaust manifold slobber. Exhaust manifold slobber is the black oily fluid that can leak from exhaust manifold joints. The presence of exhaust manifold slobber does not necessarily indicate an engine problem. Engines are designed to operate at loaded conditions. At no load or lightly loaded conditions, the sealing capability or function of some internal engine components may be adversely affected. Exhaust manifold slobber is not usually harmful to the engine, but the results can be unsightly and objectionable in some cases.
Exhaust manifold slobber consists of fuel and/or oil mixed with soot from the inside of the exhaust manifold. Common sources of oil slobber are valve guides, piston rings and turbocharger seals. Fuel slobber usually occurs with a lack of, or incomplete, or inconsistent combustion.
A normally operating engine should be expected to run for at least one hour at light loads without significant slobber. Some engines may run for as long as three, four, or more hours before slobbering, however, all engines will eventually slobber if run at light loads. External signs of slobber will be evident unless the exhaust system is completely sealed.
If extended idle or slightly loaded periods of engine operation are mandatory, the objectionable effects of the engine slobber can be avoided by loading the engine to at least 30% load for approximately ten minutes every four hours. This will remove any fluids that have accumulated in the exhaust manifold. To minimize exhaust manifold slobber, it is important that the engine is correctly sized for each application.