Never pay for a generator without watching it work under load. This 2-hour test can save you from a $30,000 mistake.

I have seen too many buyers accept delivery of a generator based on photos, a handshake, and trust. Sometimes it works out fine. Sometimes the unit arrives with incorrect components, wiring faults, or performance that does not match the specification. By the time you discover the problem, the supplier has been paid and resolving the issue becomes a negotiation rather than a right.

The solution is simple: test the generator before you accept delivery and make the final payment. This article gives you a complete testing checklist — the same one Tesla Power uses during our factory acceptance testing process. You can use it whether you are testing at the factory, at a dealer’s yard, or on-site after delivery.

Test Phase 1: Visual and Documentation Inspection

Phase 1: What to Check Before Starting the Engine

• Verify engine serial number — matches documentation, is a genuine Yuchai serial number format, and is properly recorded on the nameplate
• Verify alternator brand and model — should be Stamford, Leroy-Somer, or equivalent as specified in the quotation
• Check controller model — should be Deep Sea Electronics or equivalent as specified
• Inspect canopy condition — no dents, corrosion, or paint damage. Welds should be clean and consistent
• Verify all nameplates — engine nameplate (Yuchai), alternator nameplate, generator set nameplate with rated power, voltage, frequency, and power factor
• Check mounting and vibration isolation — rubber mounts or spring isolators should be in good condition and properly installed
• Inspect fuel system — no visible leaks, fuel lines properly connected, water separator and fuel filters in place
• Check coolant level — visible in expansion tank, correct color (indicating proper coolant mixture, not plain water)
• Check engine oil level — on dipstick, at correct level, clean oil (indicates recent change)
• Verify battery and connections — battery installed, terminals clean and tight, charger connected
• Inspect all documentation — engine certificate, alternator certificate, ISO 8528 test report, warranty certificate, operating manual, wiring diagrams, and spare parts list

Test Phase 2: Start-Up Test

Phase 2: Starting and Basic Operation

• Cold start test — engine should start within 3 attempts (10 seconds each). On a new unit with good battery, first-attempt start is expected.
• Monitor oil pressure — should reach normal operating pressure (typically 3.5-5 bar for Yuchai engines) within 10 seconds of starting
• Monitor coolant temperature — should rise gradually to operating range (80-95 degrees C) and stabilize there
• Check for unusual sounds — no knocking, squealing, metallic grinding, or irregular combustion noise
• Check for leaks — walk around the running unit and inspect for fuel, oil, or coolant leaks. No leaks should be visible
• Verify exhaust smoke — should be light gray or nearly invisible at operating temperature. Black smoke indicates over-fueling. Blue smoke indicates oil burning. White smoke (after warm-up) indicates coolant entering combustion chamber
• Check vibration — should be smooth and consistent. Excessive or irregular vibration indicates a mounting, balance, or mechanical problem
• Verify control panel readings — voltage should be within +/- 5% of nominal (400V or 230V), frequency within +/- 3% of nominal (50Hz or 60Hz)
• Run at no load for 10-15 minutes — verify stability of all parameters before applying load

Test Phase 3: Load Testing

Phase 3: Applying Load and Performance Verification

This is the most important test. The generator must be loaded to at least 75-100% of rated capacity and held at that load for a minimum of 1-2 hours.

Record all readings at each load step:

Load Level
Voltage (V)
Frequency (Hz)
Current (A)
Power (kW)
Oil Press (bar)
Coolant (C)
Fuel (L/h)

25% (skip if time limited)
Record
Record
Record
Record
Record
Record
Record

50%
Record
Record
Record
Record
Record
Record
Record

75%
Record
Record
Record
Record
Record
Record
Record

100%
Record
Record
Record
Record
Record
Record
Record

• Voltage stability — should remain within +/- 5% of nominal at all load levels. Maximum transient deviation during load step should not exceed 15%
• Frequency stability — should remain within +/- 3% of nominal. Recovery time after a load step should be under 3 seconds
• Oil pressure — should remain within specified range (typically 3.5-5 bar) at all loads
• Coolant temperature — should stabilize within normal range and not exceed 100 degrees C under any load
• No overheating — radiator should not be steaming or overflowing. All hoses should be firm but not bursting
• Exhaust smoke at full load — should remain light. Persistent black smoke at 100% load may indicate underfueling or injector issues
• Measure actual fuel consumption — if a flow meter is available, compare to specification. Should be within +/- 5% of stated figures
• Hold at 75-100% load for 1-2 hours — this is the endurance test that reveals thermal problems, leaks, and stability issues that a short test will miss

Test Phase 4: Protection System Verification

Phase 4: Verifying Safety Systems Work

• Emergency stop test — press the E-stop button. The engine should shut down immediately. Reset and restart to verify it was a normal shutdown
• High temperature shutdown — if practical, verify the over-temperature protection activates (do not force the engine to overheat — verify the sensor and controller function through the controller’s test menu)
• Low oil pressure shutdown — verify through controller test menu or by briefly triggering the low pressure alarm
• Overcurrent protection — verify the circuit breaker trips at the rated current
• Over/under voltage protection — verify the controller displays an alarm for out-of-range voltage
• Over/under frequency protection — verify the controller displays an alarm for out-of-range frequency

Red Flags: When to Walk Away or Demand Resolution

Do not accept delivery if you observe:

• Engine serial number cannot be verified or does not match documentation
• Alternator is a different brand or lower specification than quoted
• Engine will not start within 3 attempts on a fresh battery
• Oil pressure does not reach normal range within 10 seconds
• Coolant temperature exceeds 100 degrees C at any load level
• Visible fuel, oil, or coolant leaks
• Excessive black, blue, or white smoke that does not resolve
• Voltage or frequency outside acceptable range under load
• Emergency stop does not function
• Safety protection systems do not respond during testing

Green Flags: Signs of a Quality Unit

You are likely looking at a well-built generator if:

• Engine starts on first attempt and settles to smooth idle within 10 seconds
• Oil pressure and coolant temperature stabilize quickly in normal ranges
• Voltage and frequency are rock-stable under load changes
• No visible leaks at any load level, even after 2 hours at full load
• Exhaust smoke is minimal or invisible at all load levels
• Vibration is smooth and low — you can place a coin on the canopy without it falling off
• All safety systems respond correctly to test inputs
• Complete documentation package is provided with matching serial numbers

Tesla Power: Every Unit Is Pre-Tested

Every Yuchai diesel generator from Tesla Power undergoes a comprehensive factory acceptance test (FAT) before shipping:

• Minimum 2-hour full-load test with all parameters recorded
• Performance data sheet provided with voltage, frequency, current, power, oil pressure, coolant temperature, and fuel consumption at multiple load levels
• Protection system verification — all safety functions tested and confirmed operational
• Complete documentation package — engine certificate, alternator certificate, test report, warranty certificate, manuals, and wiring diagrams
• Photo documentation — photos of the unit before packing and loading
• Client welcome to witness the test at our facility or via video call

Product range: 16 kW to 1,000 kW. All Yuchai engine series. Canopy, containerized, and trailer-mounted configurations.

Frequently Asked Questions

Can I test the generator before making the final payment?

Absolutely. In fact, Tesla Power recommends structuring your payment terms so that the final payment (typically 30-40%) is released only after successful load testing. A common payment structure is: 30% deposit with order, 30% upon completion of manufacturing (before test), and 40% after successful load test and documentation verification. This protects you and ensures the supplier has incentive to deliver a unit that meets specification.

How long does a full generator load test take?

A comprehensive diesel generator pre-purchase test takes approximately 3-4 hours including: visual inspection (30 minutes), start-up and warm-up (15 minutes), progressive load testing at 25/50/75/100% with parameter recording at each step (30 minutes), sustained full-load endurance test (1-2 hours), and protection system verification (15 minutes). If time is limited, you can skip the 25% load step and reduce the endurance test to 1 hour, but I would not recommend skipping the sustained load portion — that is where most problems reveal themselves.

What equipment do I need to load test a generator?

You need a load bank — a device that provides a controllable electrical load for the generator. Resistive load banks (the most common type for testing) use heating elements to create load. They are available in various capacities (50 kW to 1,000+ kW) and can be rented from equipment rental companies. If the generator is being installed at a facility with existing electrical loads, you may be able to use the actual facility loads for testing — but this is less controllable and harder to quantify. Tesla Power facilities are equipped with permanent load banks for testing.

Should I hire an independent inspector?

For large orders (multi-unit installations, or units above 500 kVA), hiring an independent third-party inspector is a worthwhile investment. An experienced inspector knows what to look for, has the test equipment, and can provide an unbiased assessment. For smaller orders (single units below 200 kVA), if you or a qualified electrician can follow the checklist in this guide, an independent inspector is less critical — but still valuable if the budget allows. Tesla Power welcomes independent inspection of any unit.

What if the generator fails the load test?

Do not accept delivery or make the final payment. Document the specific failure (photos, video, controller readings, inspector report) and communicate the issues to the supplier in writing. A reputable supplier like Tesla Power will either repair and re-test the unit, or provide a replacement unit. The pre-delivery test exists specifically to catch problems before they become your problems. If a supplier resists load testing, that is a significant red flag about their confidence in their product.

About the Author: This testing checklist is based on the factory acceptance testing procedures used by Tesla Power for all generator set shipments. The criteria represent industry best practice and are consistent with ISO 8528 testing requirements. For test witnessing or independent inspection referrals, contact Tesla Power.