Best semi moter for fuel mileage?

Answer 1

My biased opinion, Can't go wrong with a Cummins.

And my biased opinion - Detroit. The post ACERT Cummins motors - at least to me - see to be worse for fuel mileage than their pre-ACERT counterparts.

The Mercedes-Benz MBE series (which is a Detroit at its core) and Volvo VED motors are supposed to be notably fuel efficient, but I have little firsthand experience with them (and none to speak of with the Volvo motors).

The older Volvo D12's are in fact a good engine, I have little experience with the newer updated fuel systems but they are probably the same EUI's and still running an exhaust brake vs. a compression brake. Stay away from MBE. Any savings you may have on fuel (if any) will be counter acted by the service cost. The filters alone are bloody expensive and when these engines brake, they usually brake good. Most shops I have worked at with the exception of Freightliner shy away from working on these because the attrition rate is high with these engines. I don't blame shoddy mechanics either for this. Most of the fuel connections are plastic quick fittings that become brittle, most of the fasteners are torx head and like to round out causing them to need to be drilled. This all adds up to more time in the shop and add on that not a lot of mechanics are properly trained on these engines in the USA and it is a recipe for disaster.

Now to the Detroit. I won't argue that a Series 60 DDEC V or VI is a great engine. These engines are some of the easiest to work on and have fewer moving parts than any other large displacement OTR engine. Mile for mile though from my experience the Cummins and the Detroit are both suffering due to EGR. The only difference that I see regularly is that the Cummins in shop rate vs. the Detroit in shop rate is less. I don't claim to be an engineer but I think that the Cummins has a less restrictive intake system on the ISX allowing less carbon build up on the intake ports. The other thing, and some may have noticed, is that Detroit is now buying Cummins turbo chargers to supply their engines. Cummins patented the sliding nozzle ring design on VG turbos and CAT and Detroit were forced to design a system that actually changes the pitch of the turbine vanes. Most of these fail regularly, I have seen one truck 3 times in a 1 year period for a bad VG turbo with a team driver truck at 190K, seems ridiculous. After the warranty was up they sold the truck.

What Cummins will be doing shortly will be using a waste heat recovery system to turn their engines into a partial hybrid. The EGR will have its own cooling system taking the load off the engines cooling system. The supper heated steam created by cooling the EGR gasses will be forced through a turbine to create electricity and fed to a built in motor assembly on the flywheel to assist. The steam will then be condensed and fed back through the system to do it all over. Large power plant generators currently use this technology. This adds a small recirculating pump and a small condenser in front of the radiator, not much power consumption there compared to the potential power added to the system.