What is the carbon burn rule for light loading engines?

• A. 1 hour for every 4 hours of light loading; engines must remain at 80% load
• B. 2 hours for every 4 hours of light loading; engines must remain at 60% load
• C. 1 hour for every 2 hours of light loading; engines must remain at 90% load
• D. 0.5 hours per hour; engines must remain at 70% load

Answer: (A)

When engines run at light loading for extended periods, carbon deposits can build up in the cylinders and on combustion-related surfaces. The carbon burn rule gives a practical way to clean those deposits by cycling into a higher-load condition so temperatures rise enough to burn off the buildup.

The best approach is to run the engine at about 80% load for one hour after every four hours of light loading. This balance provides sufficient exhaust and cylinder temperatures to burn off carbon without pushing the engine into high-stress operation for longer than necessary.

Other options either call for the wrong amount of high-load time or the wrong load level, which would be less effective at removing carbon or could increase wear or heat stress.