Mercedes-Benz M160 (Smart petrol, 0.6–1.5)

The turbocharged three-cylinder of the first Smart Fortwo and the Roadster — 599 cc, later 698 cc — mounted behind the rear axle, under the boot floor, and tilted almost flat.

That location is most of what makes work on it different. Access is unlike anything else in this catalogue: routine items are reached from underneath or with the rear panel off, and a job that is trivial on a conventional car is not. Read any quoted labour time as being about the installation rather than the engine.

The coolant runs the length of the car — radiator at the front, engine at the back — which makes the system slow to bleed and prone to air locks. A Fortwo that overheats after a coolant change very often just needs bleeding properly, and one that overheats otherwise is usually the pump or the long pipe runs beneath the floor rather than the head.

It is a very small engine working hard, so the turbocharger and its oil feed are the wear items, and the head gasket follows on any car that has been allowed to run hot. Cylinder head cracking is the failure that ends one. Oil condition matters more here than on a larger engine, because there is very little of it.

⚑ This page covers the Smart petrol engines, and they are not one family. The 0.6 and 0.7 are the M160 itself, and everything above is about those. The forfour's 1.1, 1.3 and 1.5 are Mitsubishi designs carrying Mercedes designations — M134, M135 and M122 — from the years Smart shared the Colt platform. They sit conventionally at the front, so none of the rear-engine access, the car-length coolant run or the small-sump reasoning above applies to them.