Hybrid vehicles only occasionally use their petrol-powered engines. Without crankcase heating up, more fuel and water dilute the oil. In addition, prolonged drain intervals contribute to oil thickening and deposit formation. These heavy deposits can impede normal piston ring function; thus reducing fuel economy, lowering power output, and increasing harmful exhaust emissions and oil consumption.

Additionally, fuel dilution and acid formation can migrate from the top side of the combustion chamber and cause the engine oil to oxidize and thicken. This leads to piston ring sticking and unstable oil viscosity. Even high-quality synthetic oils will degrade eventually. Unless the oil is fortified with enhanced protection, deposits will form on many engine components.

Hybrid vehicles are typically equipped with Stop-Start technology. This means petrol is stored in a hybrid fuel system for long periods of time before it is used. When petrol sits in a fuel system for too long, it starts to oxidize.

To make matters worse, small, high output engines are extremely sensitive to deposits that build up on fuel injectors, intake ports, on intake valves and in combustion chambers. Even small amounts of deposits cause increased exhaust emissions, reduced fuel economy and drivability problems.