Used Class 8 sleeper buyers

How Many Miles Is Too Many on a Used Semi Truck?

"How many miles is too many on a used truck?" It's one of the most common questions drivers ask when they start shopping. Is 500,000 a lot? Is a million just asking for trouble?

By Trent Benoit, Owner-Op Truck Advisors

Here's the short answer: there's no magic number. What matters is whether those miles are real miles on that engine, and whether the paperwork shows what's been done to it. Mileage is where your questions start, not where they end.

I'm Trent Benoit. I've spent 20+ years in trucking as a driver and an owner, so I've been the buyer myself, and I run Owner-Op Truck Advisors to help owner-operators make a clearer decision before a truck earns the next dollar. I take no dealer commissions. Here's how I think about miles on a used truck.

The short answer: there's no magic number

When somebody asks me how many miles is too many, my answer is that it depends on what's actually on the engine. A truck with a million miles and a complete rebuild can have fewer meaningful miles on the engine than a truck with 700,000 and no rebuild at all.

I don't have a mileage where I suddenly start asking harder questions. I ask hard questions at every mileage. A 100,000-mile truck can look better on paper than a 400,000-mile truck, but if nobody can show you a maintenance record, that low-mile truck is an unknown. A well-maintained, well-documented 400,000-mile truck worries me a lot less than an unmaintained 100,000-mile one.

Even zero miles doesn't guarantee anything. The worst truck I ever owned, I bought brand new. It had electrical problems from day one until the day I got rid of it. That truck taught me that the odometer doesn't tell you whether a truck is good. The history and the records tell you a lot more. If you're still deciding between new and used in the first place, there's a separate guide on new vs. used Class 8 sleepers.

Spend any time on the trucking forums and you'll see buyers there report both extremes: trucks they say were junk at 200,000 and trucks they say kept running well past 800,000, including million-mile trucks with documented rebuilds. Those are their stories, not data, but they make the same point. The number on the listing doesn't settle it either way.

Miles vs. engine hours and idle time

Mileage matters, but it doesn't tell the whole story. Engine hours, idle time and duty cycle help explain what the mileage means, and two trucks with similar miles can have very different histories.

Idle time is a good example. An engine that's idling isn't adding miles to the odometer, but it's still running. In my book, a truck that ran an APU is far better than one that idled.

My own rule of thumb (and it's a rule of thumb, not a measured standard) is that one hour of idle puts about as much wear on an engine as 30 miles of driving. By that math, a typical 10-hour reset is like 300 miles. A truck can rack up around 2,000 idle hours in a year, and by my rule of thumb that's roughly 60,000 miles of engine wear the odometer never shows.

So a "low-mile" truck with a lot of idle hours may not be as low-mile as it looks. The ECM data can show total idle hours along with engine hours, so ask for it.

What's been done matters more than what's on the odometer

The most important question about a high-mile truck is what's been done to the engine, and whether anybody can prove it.

Phrases like "fleet maintained," "one owner," "recent overhaul" or "rebuilt with receipts" may be true. But until there's paperwork behind them, treat them as claims. There's more on that in comparing listings that leave things out.

If the engine has had major work, ask:

• Who did the work
• When it was done
• What parts were replaced
• What the mileage was at the time
• Whether any warranty remains
• What kind of rebuild it was

That last one matters. A short block, a long block and a complete turnkey rebuild aren't the same job, and a remanufactured engine is something else again. If a listing just says "rebuilt," that tells you it isn't a reman, so your next question is what kind of rebuild was actually done. The invoice tells you how much weight to give the claim.

How the truck was used: duty cycle and the first owner

Where and how a truck ran matters as much as how far it ran. "Duty cycle" just means the kind of work the truck did: long highway runs, regional or local work with more stops, or a lot of time parked and idling. Two trucks with close odometer readings can have done very different jobs to get there.

Ask the seller how the truck was used, who ran it before them, and what kind of work it did. If it came out of a fleet, ask whether the fleet's maintenance records came with it. If the answer is vague, that's not automatically a deal-breaker, but it means you know less, and you should be more careful about what you assume.

Emissions-era trucks: ask about aftertreatment history

If the truck has emissions equipment, ask for the aftertreatment history: what's been serviced or replaced on the DPF and the rest of the system, when, and by which shop. Ask whether the fault-code history is available too.

How and when those parts wear out on a given truck is a question for a qualified mechanic, not something a listing can tell you. What you can do is ask to see the service records before you travel.

Make sure the mileage lines up

The mileage on the listing should match everywhere it shows up: the odometer, the ECM data, and any paperwork that records mileage, like work orders, inspection reports, or the title if it shows one. If those numbers don't line up, stop until it's explained. Ask the seller why they're different, and don't spend money on travel until you've got an answer that the paperwork supports.

The same goes for engine work. If there's a rebuild invoice, make sure it's for this truck and this engine.

Questions to ask the seller before you travel

Before you spend money on a bus ticket, fuel or a day off the road, get answers to these. If the truck has high miles, I start with my top three:

1. How many miles are on the rebuild?
2. What kind of rebuild was it, and are the records available?
3. Are the maintenance records available?

Then:

4. How many engine hours and idle hours are on it? Can you send the ECM data?
5. How was the truck used, and by whom?
6. Does it have an APU, or did it idle for climate and rest?
7. What's the aftertreatment history, and is the fault-code history available?
8. Does the mileage on your work orders, inspection reports and title (if it shows mileage) match the odometer?
9. Is any warranty left on the engine or major components?

For a fuller list, see the documents to get before you travel. And whatever the miles say, plan for repairs on any used truck you buy.

Get an independent inspection on the trucks that make the cut

Paperwork narrows the list. It doesn't replace a mechanic. For the trucks you're serious about, arrange an independent inspection by a shop that isn't the seller and isn't working for the seller. Ask about pulling an ECM report and doing a fluid or oil analysis as part of it.

A "DOT ready" sticker or a clean annual doesn't take the place of that, either. Here's why: DOT ready is not a pre-purchase inspection.

None of this guarantees a truck is good. It just means you're making the decision with the facts in front of you instead of a number on a listing. The Used Semi Truck Buying Guide for Owner-Operators walks through the whole process.

To be clear: it's a review of the listing and paperwork. It isn't a mechanical inspection or a recommendation to buy. You still contact the seller, get the records, arrange your own independent inspection and make the call.

More buyer tools are on the resources page.