Pullin with the dreaded PACCAR Mx13

The manual says you can use 1000ish to get to temp, and that you should NOT run the engine at low idle 600ish rpm for any sustained period of time. Like, three minutes. Personally I only run it at that for long enough for the oil pressure to go down a reasonable amount (from the 80s to the 30s PSI, happens at about 80 degrees) and then I pump it to 850-1050. It was near 0 at Iowa 80 this morning and I had to do 1050 to get to 150 deg coolant. Took like 40 minutes. Anyhow since low oil pressure at low idle is one of the two reasons (the other being emissions health) that low idling an MX13 is bad, I think letting it low idle while the oil pressure drops just a tad is fine. It is L U B R I C A T E D I suspect, though it's possible the high pressure is not inherently an indicator of that.

I'm probably going to keep this truck until the engine is at 650k miles minimum (about 240k right now/5700 hours) so mine will reach territory yours didn't have low idling.

I can tell a HUGE difference from the company 10 Roads Express T680s I drove. Mine shifts in like 3% the time the company trucks did, we thought that the 12 speeds were just sucktacular. The Volvos drove like cars by comparison.
So I'm pretty sure mine is set to "fast". My T680 feels more like an I-shift or whatever the Volvo transmission is called, it's night and day.
It also has urge to move, which I LOVE. I haven't hit a dock hard with this truck yet. If the Eaton and the PACCAR are both 12 speeds, I'm honestly not 100% sure which I have. I would hazard a guess that it's a PACCAR endurant.

The muffled jakes on this truck are the most capable I have ever used. I've never driven an old long hood, though.

I don't know what the 10 Roads trucks are/were (RIP so sad, saved me from Sysco. Never been actually SAD that a company failed before)

I suspect they were either 405MTs or 455MTs, because they were TORQUEY AS HELL but also shockingly weak in power. With like a 9,000lb postal load in a 53' van with a lift axle on the tandem (fancy schmancy for fuel economy) they'd lose speed from 67 down to the 50s on a ton of hills I pull at 70-72 with 40,000lbs in the box with this truck.

 

I read this before I headed home and did some math and did some experimentation. Everything you say makes sense, but a couple things might be wrong in non obvious ways. Well, basically just "the cruise control can do it better"
This is true, compared to a steering wheel holder givin her all she's got all the time. However, you can manually do what it does, better, because you can see the terrain. I had a somewhat heavy, in the wind, bad road quality load that took me across Iowa SR20 west and it absolutely slaughtered my fuel mileage. Cruise control at 64 was doing like 6.5! 45,000lbs in the dry van, scaled just fine, 75,000ish gross. I'm noticing a few specific things about fuel mileage particularly with this truck:

Oh, the other weird thing. These engines sorta seem to lug in the low HP, but apparently peak torque already lower RPMs. And it has simply never given me better fuel mileage than higher speeds at higher RPMs, which is crazy. Unless I go all the way down to like 60 or the 50s, it prefers 67-68 to 62-66. I think this is an RPM range thing because obviously faster requires more energy, but mine at least doesn't actually like the factory-alleged best-fuel-economy RPM range. Every MX13 powered truck I've ever driven has had a ton of vibration at lower RPMs when any torque is being used, which goes away above 1370rpm and the engine seems to quiet down and get happier. MX13s might actually like 1370-1650 most.

Every 10,000lbs removed from 45k inside the dry van is like a mile a gallon improvement, until we hit our apex of like 10.5 at 68 with an empty dry van. But 45,000 can really get you to like 6.5! I hate. Gimme them light loads pls

The wind can take you from 10 to 6mpg empty! And not just headwinds, stuff from your left or right, too.

Road quality, bumps, segmented sections, etc has a shocking effect on fuel economy if you pay attention. I'll be running nice and consistent in the countryside on a slightly goofy road, and then get to the higher quality city ring-loop-highway and fuel economy will improve at the same speed despite increased accelerations and decelerations from traffic. Additionally, these areas typically have the wind blocked off.

It appears that climbing hills is done most efficiently at peak horsepower of the direct drive gear, so like 57mph in 11th gear for my purposes. This is what the cruise control tries and fails to do when it lets you drop a couple miles an hour before adding throttle when climbing.

Cruise control is right on the money for going into neutral downhill. The rolling resistance of the drivetrain is super noticable.

What does all this mean?

Avoid state highways. Lots of stops and starts like you mention, but also GENERALLY lower road quality that is adverse to fuel mileage. Interstates often best.

Avoid roads that do not have something blocking the wind. Try not to drive across the Dakotas, Western Minnesota, Colorado, etc unless you have a tailwind.

Downhill? we goin from drive to neutral. Manual transmission guys can do this too but I'd imagine it can get annoying to get back into gear. Very easy with an automated manual, the truck knows where it is at all times. It knows this because it knows where it isn't-I mean, it knows the right RPM for any given speed to get back into gear.

Uphill? Power at 58mph in 11th, or perhaps 70mph in 12th (top of top gear's horsepower curve), depending on the load and hill. Why? Direct drive is slightly more efficient or whatever, and you're not giving up near so significant an amount of horsepower to aerodynamic forces which take over as primary problem at like 62mph or whatever. By ducking just under where that gets so bad, we're donating less fuel to god. Sometimes running up the hill at 70+mph works just fine though if it's a short enough hill/you gained enough speed from the last one.

As for the other stuff, that's the first I'm hearing of powerful jakes on a DD13. I've only ever heard the opposite as a major complaint. And yeah I can go to manual mode by pushing a button and then push the stalk shifter forward or backwards to downshift or upshift.

I should do the aero things and stick with duals. If it weren't really not worth it, I'd consider buying a trailer, too, and customizing it in a few ways. Maybe I'll get an old 10 Roads Express dry van if it's the right price, with one of those lift axles. That would probably be real fuel efficient. But if I'm paying for a trailer it should probably be a reefer or something.

I try to stop exactly twice/day. My 30 or 2/3 split, and my 10 or 7/8 split. Crappy truck stops have forced me to do more, though, and scalehouse do too sadly. I've had to leave a truck stop with a perfectly good CAT scale to another one 10 miles up the road because the place is so poorly designed. Cincinnati area truck stops ain't gr8.

 

I'd also need a different transmission, so a fair amount of stuff would have to go wrong. I wonder if I could just replace parts one at a time if they fail and keep it at current rating until I have THE TRIFECTA

 

I know it seems like I don't look at it like that, but that's mainly because I don't have it paid off yet lol. I'm already scheming for a second/backup/more ideal truck I can use for other stuff. Something I can get perfect as a backburner, that is configured ideally for the growth room that exists in trucking by escaping dry van.

Current priority spending list, in order:

Engine air filter

Brake pads service

New quality grippy fuel efficient drive tires

New fuel tank transfer valve/diagnosis of whatever is goin on. Probably the most serious problem I have on this truck is that the primary tank drains WAY faster than secondary. I'll start a day with two full tanks, and end it with primary tank at 25% and secondary tank at 60%. They sorta even out while I take a reset and my APU runs, but nobody seems to have any answers to any questions I have about it. Apparently it's different from last gen T680s (2014-2022 RIP). Regardless it's not a problem I've ever encountered before. If I ran hard for a full day, I'd probably have to take a break and let the fuel tanks even out, or fuel up primary tank. Not. Cool.
I know the engine draws from primary tank but the secondary tank NEEDS to fill the primary at an acceptable rate. Perhaps the return fuel goes to secondary too?

Thermoking APU service (oil change/belt swap/adjustment, just for the first one before I have time to go figure it all out)

Cat eyes/crossfire for drives

Random faults:

Secondary fuel tank bobber/sensor is goin bad. When it gets really cold and below 50%, it'll randomly flash "DATA ERROR" instead of a reading for a quarter of a second and the level will appear to keep going up and down. Doesn't really matter because I know 100% for sure that there's more in it than in the primary lol.
Anyhow, overall truck is low enough miles I wouldn't be surprised if I had it like 8 years or more. 371k now on truck as a whole, but like 238k on engine.

$39,500 to pay it off.