is the paccar MX13 that bad?

In the Kenworth, the MX simply was the better choice between two less than optimal choices. The ISX has bankrupted more O/O's than any other engine, between cams flat spotting, fuel pumps ruining blocks, liner issues and the early Holset after treatment systems. Yes, they can be addressed by a very savvy owner, but that's 2% of the buyers.

The MX at the time had some crank issues, the same Holset after treatment issues, and it has some other idiosyncrasies. Biggest problem is that it's proprietary, so you're pretty much tied to the dealership for service. My local dealer is excellent and reasonable, so that's not much of a negative.

My mechanic's father in law runs a fleet with several hundred trucks, and he flat out told me to absolutely NEVER buy an ISX. The failure rate in that fleet is much, much higher than with the MX.

Now, with the X15, the balance changed. Fuel pump issue appears to have been addressed, and new Holset after treatment system seems to be working just about as it's supposed to (both on the X15 and the MX). So maybe it's a horse race again.

 

I'm retired and likely won't get a chance to drive a Paccar engine, which I'm okay with.
I don't care much for electronic engines and never did, although you can't knock their efficiency over a mechanical engine.
Tasked with making a choice of buying a truck with an MX13 or X15, I would most likely choose the MX.
As for Cummins........, I was bankrupted by one of their engines in 1978 and swore I would never drive one again, but I broke that promise to help out a couple friends who I worked part time for in the early to mid 90's.
One had an older T-600 KW with a 444 Cummins and the other was a nearly new IH 9400 with an N-14.
They talked pretty sweet to get me to work for them and I accepted on the promise that if I was still working for them when they bought new trucks, that the next trucks they bought wouldn't have Cummins engines in them.
By 1996 they had a T-660 with a 3406E and a W-900L with a Series 60, they made me happy again.

 

How much is your gross weight?

 

I’ve driven one over a million miles. Been in 3 of them.. minimal problems

 

We have some in our mixers. Gross around 90k. They are always wound up past 1800 or so.

They pull fine I guess, I know they go in the shop more than the trucks with c12s.

 

1800rpm???

 

If the truck has an Allison transmission, that's not really outrageous.
Nearly every modern engine probably has a half dozen or more torque curves available for different applications and I suspect there's one or two severe service programs that they might not advertise, fire engines for example.

The severe service or high performance programming is usually a long flat torque curve that doesn't start dropping until 1500 rpm, up to 1700 rpm in some cases, and they make horsepower up to 1700 or 1800 rpm, or higher before the hp curve flattens out.

A lot of the average every day common fleet variety engine usually has a torque curve that starts to drop around 1300 or 1400 rpm and the hp curve goes flat between 1500 and 1550 rpm.

With the severe service curves and some highway scenarios, you wind up with a useable power band from approx 1000 rpm to 1700 rpm.
With the fleet curves, your useable operating range is approx 1000 to 1550 rpm.
When I say useable, I mean the point where the hp curve goes flat, makes no more power, just a flat line or starts dropping off.
They could be two identical engines with the same hp but programmed differently, the power comes on differently.
You don't really have to drive the performance engines any differently until you get into the hills and start pulling hard, and you probably won't see much difference in economy in most OTR scenarios if you drive them the same way.

 

Yes Allison auto. 5.83 gears I think.

This is in my mixer that’s usually between 80-90k gross.

It shifts at 2200 rpm or so and will hold there on hills loaded.