april2021 - 12
EQUIPMENT
Class 8 engine
rightsizing and the
impact on maintenance
and longevity
How fleets can choose engines
that will provide the best
balance of safety, performance,
efficiency, and durability.
By John Hitch
[ POWERTRAIN ]
T
here is always a certain amount of pressure on fleets and owner-operators
to " get it right " when spec'ing a new truck. In a business with such slim
margins, a slight miscalculation can snowball into a mountain of money
lost over the life of a Class 8 tractor.
Some boxes are fairly easy to tick, like a sleeper versus day cab, based on
application, be it regional, long-haul, or vocational.
But that is not always the case. Choices such as using the most optimal
low rolling resistance tires can save several thousands of dollars or more,
but nothing impacts overall performance of a fleet more than the diesel
engine. This is the general premise of engine rightsizing, which traditionally
can mean dropping down in engine displacement, sometimes even down in
vehicle class, to increase efficiency and not have more power than necessary.
'No replacement for displacement'
In the heavy duty segment, the first question to answer is " how big should
the engine be? " Or rather, " what is the displacement? "
Displacement is measured by the diameter of the pistons or bore. Currently
for Class 8 trucks, at the lower end this is around 10L to 11L, around 12L
to 13L for midrange, and around 15L at the high end. Usually, the number
designation approximates the displacement volume. Paccar's MX-13 is 12.9L
while Detroit Diesel's DD13 is 12.8L. This is not always the case, however,
as the Mack Trucks MP8 is 13L.
Simply put, the higher the displacement, the more power the engine outputs.
Fleets needing more power (construction, off-highway, heavy haul, varied
elevations) have veered toward higher displacement engines, but current
technology has allowed fleets to utilize more options and a more equitable
compromise between performance and fuel and operational efficiencies.
The load requirements for a truck are a jumping-off point.
" If you're going to be doing anything over 80,000 pounds, you're not
going to want to look at a DD13 engine; you're going to want to look at
12 Fleet Maintenance | April 2021
»A Cummins worker at the Jamestown Engine Plant in Jamestown,
New York, assembles an X12 engine, which was launched in 2018 to offer
customers a more modest displacement (11.8L) than the X15 (14.9L).
The X12 is currently available with Freightliner, Western Star, Autocar,
Oshkosh, Terex, and several other specialty truck manufacturers.
Photo courtesy of Cummins
april2021
Table of Contents for the Digital Edition of april2021
Uptime
Editor's Note
Class 8 engine rightsizing and the impact on maintenance & longevity
Gremlins and ghosts
Staying safe in the shop
Avoiding turbocharger trouble
10 steps to assess the parts storeroom
Monitoring economic recovery progress
Fleet Parts & Compenents
Tools & Equipment
Classifieds
Diesel fuel additive considerations
april2021 - 1
april2021 - 2
april2021 - 3
april2021 - 4
april2021 - 5
april2021 - 6
april2021 - 7
april2021 - Uptime
april2021 - 9
april2021 - Editor's Note
april2021 - 11
april2021 - Class 8 engine rightsizing and the impact on maintenance & longevity
april2021 - 13
april2021 - 14
april2021 - 15
april2021 - 16
april2021 - 17
april2021 - Gremlins and ghosts
april2021 - 19
april2021 - 20
april2021 - 21
april2021 - 22
april2021 - 23
april2021 - Staying safe in the shop
april2021 - 25
april2021 - 26
april2021 - 27
april2021 - 28
april2021 - 29
april2021 - Avoiding turbocharger trouble
april2021 - 31
april2021 - 32
april2021 - 33
april2021 - 10 steps to assess the parts storeroom
april2021 - Monitoring economic recovery progress
april2021 - Fleet Parts & Compenents
april2021 - 37
april2021 - Tools & Equipment
april2021 - 39
april2021 - 40
april2021 - Classifieds
april2021 - Diesel fuel additive considerations
april2021 - 43
april2021 - 44
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