is the paccar MX13 that bad?

How often was the oil changed? 20K interval?
Was the overhead ran yearly?
Any of these new engines will last longer if you do not fallow the manufacturer guidelines.
If you go 50K on oil they will loose rod bearings, or spin main bearings.

 

Details are sparse, but one thing to consider is the way the trucks are driven, or programmed.
If you're pulling heavy loads and running the engines at 1100 or 1200 rpm and it's working fairly hard, the cylinder pressures are a lot higher than at a higher rpm and create more heat and put heavy strain on the components causing premature wear and/or damage to the engine. (head, rods, crank, etc)
Running at 1200 rpm is okay for half a load, but you put some weight on or buck a nasty wind, you're better off to drop a gear and run at 1500 or 1600.
If you read the literature for the engine there's likely a reference to increasing engine speed when pulling loads over 80,000 lbs.
I know I've read that in Cat literature, but the physics in every brand of engine are the same and should apply universally.
(suck, squeeze, bang, blow)

 

But lugging my engine gives me very good fuel mileage.
Aren't new engine literature telling owners to run on torque when loaded??

 

Yes they are, but they're talking about the 70% of the trucks that run half loaded all the time, or under 80,000 lbs.
Torque has nothing to do with getting you down the road, it's the horsepower that's measured.
It takes X amount of horsepower to maintain a given speed, so if you're engine is capable of making 500 hp at 1200 rpm and it only takes 200 hp to keep you rolling at desired speed, torque doesn't really matter, only that you're operating in the engines power band, which hp and torque curves will show you.
Just because the engine is spinning faster doesn't mean it's using more fuel, because if you drop a gear to maintain a given speed. it's not working as hard and your gauges should show it.

I looked but couldn't find anything for Paccar, but I found the Cat literature, should say nearly the same thing.

http://www.performancediesels.co.nz/vdb/document/6

80,000 lb GCW or less

Less than 1750 lb-ft: 1400 rpm @ 65 mph (105 km/h)

1750 lb-ft and above: 1325 rpm @ 65 mph (105 km/h)

90,000 lb GCW or more

1500-1650 rpm @ cruise speed

Multi-torque: 80,000 lb GCW or less

435-hp, 1550/1750 lb-ft: 1325 rpm @ 65 mph (105 km/h)

475-hp, 1650/1850 lb-ft: 1325 rpm @ 65 mph (105 km/h)

 

Here's a video that explains rpm and torque pretty well.

 

I do not see a truck engine lasting long if landed near 80k bucking wind, and going uphill if your keeping rpm under 1400 rpm.
But that's just me.

I sure do respect Rawze, but I can not respect that Cummins ISX.

 

Yup the MX sucks...

@Caesar @daf105paccar

 

I'm biast.
I've earned a lot off money with my MX.

@Cat sdp
Allready read this thread.

Ps caesar cannot see you mentioned him.
Should have put a space between the . and the @