GE steam turbines till late 1980's and then Sulzer diesels.
My last ship was steam turbine.
I ran bunkers on the Great Lakes, mainly Lake Superior, which is a bulk cargo port (stone, ore, coal, grain.) Lots of V-16 Pielsticks on the US side, which were sold and serviced by Colt. The chiefs were very fussy, for the most part, insisting on 11.7 API and 151 visc for a 280 CST. Most of our feed was about 380/400 CST, so this was about a 2-3 percent blend with N2. One boat stipulated 270 centistokes and that's what we made up. We also had Canadian and "salty" vessels via the Seaway. Some Europeans asked for IFO 60 or IFO 100 which we could make via our tanker's inline blending capability. I met a lot of good people from this trade. Always fair and usually got an initation to have dinner if they were in port for a while.