Reliability of Paccar MX-13 vs cummins X-15, what do you think?

When I have people ask about difference between the engines my first question is......what are you doing with it? Please give details on your typical application and carrying conditions.

Yes the aftertratment systems are idetical and both manufactured by Cummins. There are more MX powered trucks out there in the stock piles than Cummins. Stock levels were depleted and new truck lines were bare due to plant shutdowns from Covid.

 

I have run both and currently own a MX-13 powerd truck, so i can give you MY opinion on it which with a wooden nickle might get you some coffee. That said the X15 has a lot more power and torque. Mileage is simular if speced simular unless you lay into the X15. MX-13 parts are more expensive by a LOT and can only be serviced by a dealer. But the X15 tends to go in a big way when it goes see spalling fuel pump incident for example. Both require regular DEF and EGR system service (i recomend at least once a year) or things go badly for you. The MX struggles hard on hills even when tuned to 510 it just doent have the umph of a X15 but its also quite useable.

Mx13 has a hard time being rebuilt so tends to need to be replaced rather then overhauled but also typically live to 1 million. X15s are easier to rebuild but depending on useage tend to need a rebuild more often. MX13 also has a few flaws in it like the plastic coolant fittings. X15 handles ideling better then the MX13 and wont clog as fast but its still an emissions truck. MX13 requires a fuel filter change every 15k if you even so much as let bio diesel look at it or it will throw a check engine derate at you. X15 is more tolerant of sloppy maintaince. Also the MX13 requires super expensive software (15-20K a year) to do ANYTHING with the computer. X15 is MUCH easier to tinker with if you need to say do an override to limp it the 5 miles to a shop.

Least that is my personal opinion.

 

If you are patient and want to make more money by saving fuel and like a quiet engine, I would go MX. If you want to pull a mountain faster than the other guys and can afford the higher fuel bill then go with the larger displacement Cummins. In the end the Cummins will not come close to the fuel efficiency of the MX under the same foot. MX torque and RPM curve is lower.

I agree Cummins is easier on the DIY guy and offers more service options over the road.

Dont idle either one.....

 

Depends on if you pull 80k+ on a regular basis or not the X15 is about the same fuel consumption wise overall. i have found on average my mx gets around 6mpg hauling 80k daily and the x15 got around 5.7 average so simular mpg or at least close enough to be a wash. Additionally the MX burns a lot of fuel getting back up to speed with a 1650 torque vs a 1850 or 2050 of an isx. Also of note is my mileage falls out the floor in mountains. For example an average of 3.5 to 4 in VA where the X15 got 5 driving exactly the same. Though the MX gets 7 on flat country where the X peaked at 6.3 so again a wash for me.

Back to @c.w though yes the paccar is innemic as hell and takes a long time to get up to speed on even flat ground and is capped at about 20 on 64 in va for example. X15 was doing 45-50 which can cause problems insofar as scheduleing. The MX13 brake is deceptive though, super quiet but i feel its stronger then the X15 but thats my opinion again.

 

We have 579 Epix packages closing in on 10mpg with speed limiter and idle shutdown enabled. No X15 I have seen will even come close to that number in the same chassis/set up.

But again its all in the set up and how you drive and maintain it.

You say they are the same it your experience. I'm sorry I disagree.

MX has the edge on fuel economy, hands down. Thanks for sharing your experiences.

 

Ah there is where the disconnect is. You are using your trucks as standard road trucks. My experince is vocational useage. I use a 579 as well with an MX13 but its tuned for power and pulling with most of the economy features discarded just due to what my useage requires.

Im a rock truck so i have my speed governer shut off entirely as well as most of the idle shutdown and rpm limits turned off paired with a higher gear rateing then you likely use. With my engine set up in this manner its quite simular mpg wise to an X15 in a simular truck (T680 is what i used) and as i am paid by weight none of my loads are under 79k gross....ever. In a van or reffer truck i have no experince to say.

So i will say the same to you that i disagree with your own experinces from my point of view. Then again as i also said the way i use my truck is likely quite a bit diffrent then your own.



Doing this kind of work murders a MX in mpg. Still better then a kitty though and dont say its sloppy maintaince. I have a recipt book 6 inches thick and $40k in one year that disagree with THAT statment

 

Just to note the use doesn't limit the ability to use many of the efficiency features ...it's an operational decision.

Fuel is the #1 easiest and biggest expense that can be controlled.

Idle shut down can be setup where PTO doesn't interfere

Top speed limit - this is a big one that can easily be turned on to limit drivers bad speeding habits and poor speed control habits (pedal jockeys)

High drag applications use significantly more fuel as speeds go up from 60mph.
.by 70 mph it's guzzling fuel badly just to push wind.

Enable a split speed RSL for pedal vs cruise to favor more economic cruise use with 5mph or more of rollout.

Gearing - most mild downspeed gears of 2.64-3.08 can be used in these modern high tq low rpm motors with very little change in pulling power at all but significantly better fuel mileage