The Cummins L Series engine is a straight-sixdiesel engine designed and produced by Cummins. It displaces 8.9 litres (543.1 cu in), and began production in 1982 as the L10. The engine was based on its 8.3 litres (506.5 cu in) predecessor, the Cummins C8.3 engine and which like the current ISL, had seen use in the applications listed above. It displaced 10.0 litres (610.2 cu in), and was available in either a vertical form, for upright use in trucks and buses, or horizontal form, for underfloor use in buses and trains. The L10 was Cummins first competitive offering in the British bus market, as their earlier production had been too large and heavy. However, it had a troublesome introduction to the British market, with high oil consumption and sealing problems.
By 1994, it had been developed into the M11, and in 1998, Cummins ceased production of the old L series engine. The L10 became the ISL when the Interact System was added.
The Cummins ISL also has a sister engine which is based on the existing ISL 8.9 litre cylinder block which runs on compressed natural gas (CNG). The engine was introduced in 1992 as the L10G before being replaced by the L Gas Plus in 2001 until it became the ISL G in collaboration with Westport Innovations in 2008.