2006 Harley-Davidson Street Bob (EFI) — Owner's Manual
In colder climates, the engine oil change interval should be shorter than normal. Motorcycles used only for short runs must have the engine oil changed more frequently and have a thorough tank flushout before new oil is put in. See an authorized dealer. NOTE: The further below freezing the temperature drops, the shorter the oil change interval should be.
Water vapor is a normal byproduct of combustion in any engine. During cold weather operation, some of the water vapor condenses to liquid form on the cool metal surfaces inside the engine. In freezing weather this water will become slush or ice and, if allowed to accumulate too long, may block the oil lines and cause damage to the engine. If the engine is run frequently and allowed to thoroughly warm up, most of this water will become vapor again and will be blown out through the crankcase breather.
If the engine is not run frequently and allowed to thoroughly warm up, this water will accumulate, mix with the engine oil and form a sludge that is harmful to the engine.