# Ten Walk-Away Signs at a Truck Inspection

> Signals that tell you the truck you're looking at is about to cost you more than you can afford. When the evidence says no, even if you want to say yes.

Updated: 2026-08-22. Source: Big Rig Risk — https://bigrigrisk.com/guides/when-to-walk-away/ (claims cited to primary sources; see /methodology/).

An owner-operator walks into a used-truck inspection hoping to walk out with a deal. That hope is the enemy. Trucks that look fine and drive fine can carry repair bills that end a business. The walk-away signals exist to protect you from the ones that should never have been for sale in the first place.

## Signal one: no maintenance records, and the seller does not care

A truck with silence where the records should be and a seller who says "it runs fine" is a truck saying its next owner will finance its deferred maintenance. Walk. The odds of finding an engine inside that truck that has been properly serviced and undocumented are too low to bet your livelihood on.

## Signal two: no fuel pump record on a ceramic-plunger year

Ceramic fuel-pump plungers starting in 2010 are the headline defect on the ISX15, and Cummins moved to steel plungers around 2017 to fix it. If the truck falls in that 2010 to 2016 window and the seller cannot produce a pump service or replacement record, the truck is telling you the event is still ahead of you.

Do not treat 2017 as an all-clear either. Our own record flags that fix as partial at best, because a mechanic on camera says the pump kept causing trouble from 2017 all the way through 2021. The tells he lists are rough idling, excessive smoke from the stacks, and extended cranking. If you see any of those on a truck with no pump paperwork, regardless of year, you are looking at the failure in progress.

We are not going to quote you a pump replacement price, because we could not source one we would stand behind. Get a written quote from a shop before you make an offer, and price it in. Walking is the right answer when you cannot get that number and the seller cannot produce the record.

## Signal three: the engine computer shows derate faults, and they got cleared

Pull the fault-code history yourself, or have a diesel tech pull it at a shop you choose rather than one the seller recommends. It runs about $150, which makes it the cheapest evidence in this entire process.

If the history shows derate codes that then disappear, that is not a repair. That is somebody hitting clear before the listing went up. A derate code is the engine reporting a fault. Clearing it changes the report, not the fault. Ask what the codes were covering. If the seller will not say, walk.

## Signal four: top-end ticking that does not go away

A cold-engine tick that quiets down after the oil circulates is normal. A tick that stays while the engine is warm and gets worse on acceleration is not. That is broken valve train. On an ISX15, that can be a valve spring, a rocker arm, or a more expensive problem hiding underneath. Have a shop do a borescope if you hear it and you like the truck. If it is broken valve train, walk.

## Signal five: rough idle or stalling when you rev and let off

That is fuel system or EGR. On these engines it is usually carbon in the EGR valve or the fuel pump starting to die. A rough idle at operating temperature is not going to get better. Walk or price a fuel-system job into the offer and know what you are buying.

## Signal six: blue or white smoke from the exhaust, especially cold start

Blue smoke means oil is burning. On a high-mileage engine, that is a sign the piston rings are worn. White smoke can be water in the combustion chamber, which usually means a head gasket or cracked head. Neither one is a quick repair. If you see it and the seller dismisses it, the repair is going to be your problem. Walk.

## Signal seven: blown-by so heavy you can see it

Pull the dipstick while the engine idles and look for a strong breeze coming out of the tube, or check the breather. Heavy blow-by means combustion pressure is getting past the rings, and on an engine with real mileage on it that means a rebuild rather than a repair.

Our Detroit DD16 record has this exact case documented: active blow-by from the breather led directly to a full in-frame rebuild, and the invoice for that job was $36,000. Different engine family from the Cummins engines most of this list is about, so do not read it as an ISX15 price. Read it as what the symptom is worth taking seriously.

## Signal eight: a head bolt that is broken or was ever broken

A mechanic in our record reports broken cylinder head bolts recurring across multiple ISX15 engines he has serviced, and he traces the chain: bearing replacement that got deferred, then spun main bearings, then broken crankshaft and cylinder head bolts. His words are that if you do not replace it on time, you are going to get this issue.

So a broken or replaced head bolt is not the problem. It is the receipt for a problem that happened earlier and further down in the engine. A head bolt kit itself lists at $395, which tells you the bolts were never the expensive part. Walk, or commission a full engine inspection and expect to pay for what it finds.

## Signal nine: a spun main bearing in the history, or evidence of one

Same chain, caught one stage earlier. If any mechanic has found and documented a spun bearing on this engine, walk.

The reason is not the bearing. It is that the bearing spun because the service that would have prevented it did not happen, and whatever else that neglect touched is still in the engine. Buying it means buying the parts of the chain nobody has found yet.

For scale on what a full teardown costs once it reaches a dealer, our Volvo VNL 860 record captures an invoice read on camera at $34,090.58. That was a D13, not a Cummins, and the cause was coolant leaking internally from number six cylinder rather than a bearing. We name the engine and the cause because a number like that gets quoted loose, and a loose number is worth nothing to you. What it establishes is the ceiling: a full dealer overhaul on a Class 8 diesel is a five-figure event in the thirties.

## Signal ten: EGR cooler that is leaking or was welded back together

The EGR cooler leaks coolant into the combustion chamber on ISX15 engines. If it is leaking now, you are buying the repair. If it was welded, the weld is a patch, not a fix. Both are walk-aways.

## The honest counterweight: not every repair is a catastrophe

A list like this can talk you out of every truck on the lot, so here is the other side of it, with sourced numbers.

One in-frame job documented in our record covered intake valve reseat, valve springs, and new cam bearings for $4,600 in parts and labor. The mechanic published it specifically because, in his words, a lot of the in-frame cost claims online are exaggerated and he wanted real numbers out there. On the parts side, priced from a live retail catalog on 2026-08-19, a complete Cummins ISX15 overhaul rebuild kit lists at $3,295 and the X15 kit at $3,995. An upper gasket set is $795.

That is the distinction worth holding. Known work with a scope and a quote is a purchase decision. The ten signals above are different, because in each case the visible symptom is downstream of something nobody has priced yet.

## What all ten have in common

None of these get cheaper by waiting, and none of them are things the next owner can afford to discover twice. They separate the trucks for sale because somebody is upgrading from the trucks for sale because somebody knows what is coming.

If you hear yourself thinking "well, maybe I can fix that myself" or "I will get it serviced right after I buy it," you have already failed the walk-away test. The truck is going to cost you exactly what it should have cost its previous owner, and he is about to transfer that problem to you. Do not carry his debt into your next venture.

See the full inspection framework: [the used ISX15 and X15 buying guide](/guides/used-isx15-x15-truck-buying-math/). The step-by-step walkaround: [pre-purchase inspection for a Class 8 truck](/guides/pre-purchase-inspection-truck/). The pump years in detail: [ISX15 years to avoid](/guides/isx15-years-to-avoid/).