Buying a higher mileage emission motor?

Neither. If they said the emissions system has been done, unless it has a warranty. They lied. They likely did a regen and called it good. Also whats your budget, we may be able to point you to a better unit.

As for a used rig. If you buy a used emissions rig. Your just add the cost of dropping the entire emissions system, having it cleaned, new doser, having the egr pulled and cleaned, the high pressure line pulled and cleaned a def flush and new filter, new lines and all new clamps and gaskets to the price (about 10k) or dont even bother. With an ISX, get a warranty or dont do it. Injectors like to go pop around 500k and they are around 7K EACH to do individually and around 12-15K to do all at once with cups.

They are good motors from my sofar limited experince but they do have a list of known issues.

 

Definitely the Peterbilt, if I had to pick between the two. Anyone will work on a Paccar product, Mack, if it’s anything electrical, it’s going to the dealer. Peterbilt will ride, and handle better as well. Build quality is superior to Mack. And yes, I’ve run both. My ‘93 Pete was better than that brand new Mack was. As far as emissions, if it’s a day cab, it likely stays reasonably local, I’d run it until the emissions cause a problem, then fix them permanently. How many hours on the engine? I just bought a truck with an ISX several weeks ago, it’s my first Cummins, so I don’t profess to be an authority on them, talked to my local mechanic, and he said they are as good as anything else produced in the last 15 years. He said in his opinion, 35-40k hours is where they like to grenade.

 

Since neither is a charm, I'd go with the Pete strictly for resale. 389s are awesome trucks. You are gravitating towards trucks that don't really classify as "old", its just, 400K is normally when the bottom falls out, and a complete major is usually next. Remember, day cabs are usually a lot more worn than OTR trucks. While they may have lower overall mileage, they endure the rigors of daily P&D, and I'd almost rather find a decent OTR truck and use it. Then, if the local goes bust, or mom gets upset, you have a sleeper already. I've taken sleeper trucks just about every place I took a day cab. Low mileage trucks don't exist, and if you are buying something used, get used to the fact, it's going to be USED! Sadly, if "budget" is an issue, you are setting yourself up for failure.

 

I have one truck with 2 million miles on it, been overhauled 3 times. Twice was me. The biggest thing is, don’t go cheap when you do need to overhaul it. I did the first time, was a dumb mistake. Keep up on your maintenance, oil changes etc, and I think that truck will serve you well for many years

 

Just remember, there's a reason they're selling it.