The earliest 300SE/SEL used an oddball M104.990 3.2L LH-injection six, unique to the W140, rated around 228 hp and 229 lb-ft and considered notably torquier than the CIS-E M104s in the W124/W129. The short-wheelbase 300SE/S320 is called out as the sweet spot of the six-cylinder cars, and these engines are cited running to very high mileage (one owner referenced a 630,000-mile 1997 S320).
M104 inline-six (300SE/S320) character and desirability
Mercedes-Benz S-Class (W140) · mechanical