Buying a used Class 8 truck or commercial vehicle that you plan to finance? A pre-purchase inspection from a qualified mechanic is the single best protection against expensive surprises. Here is what to check and what to document.
Engine and powertrain
- Engine oil sample analysis (look for metal particles, glycol contamination, fuel dilution)
- Compression test on each cylinder
- Turbo and exhaust manifold inspection (leaks, cracks)
- Cooling system (radiator, hoses, water pump, EGR cooler condition)
- Aftertreatment system: DPF (Diesel Particulate Filter) condition, SCR/DEF system, NOx sensors, regen history
- Transmission: shift quality, fluid condition, prior rebuild history
- Differential: oil sample, gear noise, prior rebuild
- Drive shafts and U-joints
Frame and chassis
- Frame rail inspection for cracks (especially near saddle area, fifth wheel mount, suspension mount)
- Cross-member condition
- Suspension components: airbags, leaf springs, shocks, bushings
- Air system: leaks, dryer condition, governor cut-in pressure
- Steering: gearbox, drag link, tie rod ends, kingpin play
- Fifth wheel: top plate, locking jaw, height, pivot
Brakes
- Foundation brakes: shoe and drum thickness on each wheel position
- Air system: pressure tests, leak-down test, slack adjuster operation
- ABS warning lamp and function
- Brake balance under loaded condition (if test-drivable)
Tires and wheels
- Tire depth on each position (steer minimum 4/32″, drive/trailer minimum 2/32″ DOT)
- Sidewall condition (cracking, bulging)
- DOT date code (avoid tires over 6 years old regardless of tread)
- Wheel and rim condition (cracks, bent flanges)
- Spare and tools
Electrical and HVAC
- Battery condition and charging system test
- Starter draw test
- All lighting (DOT-required + cab interior)
- Heater, AC, defroster operation
- Dashboard gauges and warning indicators
- ECM data: total miles, hours, fault history (request OEM diagnostic pull)
Cab and interior
- Door seals and hinges
- Window operation
- Driver seat condition (airbag suspension on premium trucks)
- Sleeper condition (if applicable): mattress, AC, refrigerator, inverter
- Wiper operation and washer fluid
Documentation to request from seller
- Maintenance records (full service history, ideally from OEM dealer)
- Carfax / VIN history report
- ECM mileage history pull
- Prior DOT inspection records
- Title with clear lien status (no active UCC or DMV liens)
- Any warranty remaining (transferable extended warranty is gold)
What to budget for inspection
Qualified Class 8 truck inspector: $250-500. Mobile inspection (they come to you or the seller): $400-800. Pre-purchase inspection by an OEM dealer (Freightliner, Kenworth, Peterbilt, Mack, Volvo): $300-600.
Red flags that warrant walking away
- Frame cracks anywhere
- DPF aftermarket “delete” (illegal; will fail emissions inspection)
- Coolant in oil or oil in coolant (head gasket or EGR cooler issue)
- Major recent paint work hiding rust or accident damage
- Maintenance records gaps over 6 months
- Title issues (salvage, branded, prior repo on a recent title)
- Excessive ECM fault codes with active warning lights
What lenders require
For used trucks financed over $25,000, most lenders require a third-party inspection report. The lender may have an approved inspector list or you can use any qualified mechanic. The report goes into the underwriting file along with the equipment quote and bank statements.
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