Quick answer
Obtain the exact model, serial number, rating plate, manuals, ownership record, hours, service and repair history, fuel and duty history, storage history, controller and firmware information, emissions label where applicable, and transfer or distribution documentation. Inspect cold, witness a cold start, and arrange a qualified load and electrical test appropriate to the intended use. Price every missing record as risk and walk away from unsafe modifications, unclear ownership, damaged conductors, serious leaks, unstable output, or an unsupported model.
Verify identity, rating and lawful ownership
Photograph the complete rating plate and record model, serial number, manufacturing information, voltage, phase, frequency, power rating and duty, power factor where shown, fuel, current, outlets or terminals, and emissions labels. Match these to manufacturer records and current manuals.
Confirm the seller owns the equipment and can provide a bill of sale with the serial number. Investigate removed plates, altered hour meters, mismatched enclosure parts, unexplained repainting, and conflicting records before money changes hands.
Reconstruct use and maintenance history
Request hour-meter photos over time, maintenance invoices, oil and filter records, battery dates, coolant service for liquid-cooled units, valve service where applicable, fuel-system work, alternator or controller repairs, load tests, alarm logs, outage hours, rental history, storage conditions, and reason for sale.
Hours alone do not establish condition. Long low-load operation, missed calendar service, stale gasoline, water intrusion, overheating, overloads, repeated fault resets, and years without testing can matter more than a modest hour number. Treat missing records as an inspection cost and uncertainty allowance.
Inspect the machine cold before it can hide symptoms
Look for oil, fuel, coolant, exhaust, and battery leakage; corrosion; rodent or insect damage; blocked cooling paths; cracked insulation; overheated terminals; damaged receptacles; improvised bonds; missing guards; loose mounts; worn hoses and belts; contaminated fluids; and evidence of flood or fire exposure.
Check that the engine is genuinely cold before the first start. Observe cranking speed, smoke, noise, vibration, warmup, charging, leaks, controls, voltage and frequency indications, and shutdown. Never run a combustion generator indoors for inspection.
Test output under a controlled load that answers the intended question
A receptacle voltage reading at no load is not a capacity test. For portable equipment, test protected outlets and generator behavior with a controlled permitted load. For larger or commercial equipment, arrange qualified load-bank and insulation or electrical testing appropriate to the machine and purchase value.
Record voltage, current, frequency, load, phase balance where applicable, recovery, temperature, alarms, leakage, and shutdown. If the seller refuses a reasonable independent inspection or load test, price the unit as unverified or decline it.
Confirm system fit and calculate the catch-up budget
Verify voltage, phase, outlets or terminals, neutral configuration, GFCI behavior, transfer compatibility, controller, fuel pressure, placement, clearances, emissions eligibility, sound, parts availability, service access, and manuals. A bargain 120-volt unit does not fit a 240-volt load, and a three-phase set does not become a household source through an adapter.
Add immediate fluids, filters, battery, tires, hoses, belts, plugs or ignition parts, coolant work, carburetor or injector service, controller replacement, cable and transfer equipment, transport, rigging, permits, testing, and professional installation. Compare the verified total with a supported new or rental alternative.
Frequently asked questions
Common questions
How many hours is too many on a used generator?
There is no universal cutoff. Duty, loading, fuel, maintenance, age, environment, repairs, rating class, and test results determine condition. Compare hours with the exact manufacturer service and life information.
Is a no-load start enough to buy a used generator?
No. It does not prove regulated output, load acceptance, cooling, fuel delivery, alternator condition, outlet protection, or compatibility with the intended system.
Should I buy a used generator with no maintenance records?
Treat it as higher risk. Budget a qualified inspection, testing, overdue service, and possible hidden repairs, or decline the purchase when the value does not justify that uncertainty.
Can an electrician inspect the engine too?
Electrical and engine expertise may come from different qualified providers. Larger purchases can justify both generator-service and electrical-system review.
Primary references
CordFind summarizes connector specifications and public safety guidance. Always follow the instructions supplied with your equipment.