CARBON BUILD-UP

Many manufacturers are now employing direct-injection petrol engines. While doing some research on this technology, it appears that, after a few years, owners will encounter some serious issues due to carbon build-up on the inlet valves. This will probably happen as soon as the warranty expires and will not be a cheap repair. What recourse does the owner have, as this is essentially a design flaw? FREDDIE VAN LEEUWEN Via email It’s an interesting question and we’re planning a tech article on the subject for a future issue (also see page 114 for a humorous insight).

With the introduction of direct injection, carmakers and oil companies have been working together to find a solution to the carbon build-up on inlet valves. The fuel in port-injection engines carries the necessary detergent properties to keep the valves clean. The solution was an additive for the oil designed to leak past the valve stem seals (in minute quantities) to keep the intake valves clean.

This has mostly solved the problem but, worryingly, carbon build-up is still present in some engine designs. It may lead to a drop in engine performance and driveability problems but would rarely destroy an engine. We doubt manufacturers would cover damage outside warranty, though.