Asked by: Toby Graham, Shrewsbury
Things tend to get dirty and worn over time. Air filters and exhausts can clog up, blocking airflow to and from the engine; fuel injectors and spark plugs can get mucky, causing less efficient firing; and fuel pumps can wear out and no longer pump fuel so well. Meanwhile, combustion byproducts can form deposits, stopping engine valves closing, reducing pressure generated by the burning fuel and causing backfires.
More seriously, inside the engine the piston rings can wear down, reducing the pressure in the cylinders and lowering the power output. Keep your car serviced regularly, though, and a modern engine should only lose a few per cent of horsepower over hundreds of thousands of miles.
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