Today’s catalytic converters burn away most gases entering them, leaving no tell-tale oil smoke at the exhaust pipe.
Direct injection engines burn leaner than port fuel injection engines, up to 60-to-1 versus 14.7-to-1 air-to-fuel ratio.
A leaner mixture results in more conservative fuel usage but contributes to much hotter engine operating temperatures.
Higher cylinder temperatures and pressures released into the crankcase accelerate oil vaporisation, resulting in oil droplets coating intake valves.
The cylinder injector spray position means fresh fuel is not sprayed onto intake valves to flush away vapour build-up.
This build-up can accumulate and bake onto intake valves in as little as 10,000 miles.
Rings can become stuck into their lands by carbonised oil sludge, preventing the low-tension rings from properly sealing the piston.
This also causes sludge, oil and fuel deposits to bake onto piston tops.
Direct injection engines are renowned for coking – a build-up of cooked fuel deposits that foul injectors.
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