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Generator Service and Preventive Maintenance

Any generator set used for emergency or primary source must have periodic service and maintenance performed. Setting up a planned maintenance schedule, and performing all associated testing will insure generator availability upon demand. Possibilities of generator failure increase when service and maintenance checks are not performed.

The templates on this page are for reference only and to establish the basic contents of a planned maintenance schedule. Always create the planned maintenance schedule in accordance with manufacturer’s guidelines.

Concept of Planned Maintenance

Planned maintenance can be defined as performing service, maintenance, inspections and testing on a generator set on a pre-determined schedule. Each maintenance program should include inspections for the status listed below:

  • Calendar Cycle Schedule – Depending on manufacturer recommendations and applications, cycles can be divided into weekly, monthly, quarterly, semi-annual and annual requirements.
  • Operating Inspections – Inspections to be performed on generator when operating. Critical operations can be monitored 100% of operating time. Non-critical operations can have basic checks performed as determined by application.
  • Layup – Generator are placed in layup when no longer in active use. Basic outline of steps for generator layup.

A selected generator style (Portable, Skid and Weathertight Enclosure) will be featured to illustrate the basic creation of the inspection.

The final section introduces Diesel Service and Supply as a provider for Service Contracts for all generator sets sold.


Figure 1, Diesel Service and Supply

Visual Checks

Do not remove the pressure cap from a hot engine. Wait until the coolant temperature is below 120°F (50°C) before removing pressure cap. Heated coolant spray or steam can cause injury.

All planned maintenance charts define checks to be completed at a calendar interval. Coolant, lubricating oil and coolant levels can be at normal levels, but can be contaminated (Figure 2). When performing normal maintenance inspections look for the following:

  • Air Restriction Indicator – Indicates when air restriction to intake is greater than manufacturer specifications. Red in color means change air filter (scheduled or not). Generally indictor located on air filter housing. Can be reset after filter change.
  • Fuel Water Separator – This filter separates water from fuel contaminated with water. Water is routed to bottom bowl and can drain via valve. This can indicate main fuel source supply is contaminated.
  • Water Indicating Paste – Used to test main fuel supply. Spread on tank level stick. Pink in color with no water. Turns red when fuel is contaminated with water. Generally water at the lower section of tank.
  • Oil in Coolant – Oil floating on the coolant when cooling system is at ambient temperature. Can appear milky after engine operation. Engine lubricating oil leak into cooling system. Can be cylinder head gasket, defective engine block or cylinder head. Defect is where oil pressure is higher than coolant pressure.
  • Coolant in Oil – Oil has milky color on dipstick. Coolant leak into engine lubricating oil. Can be cylinder head gasket, defective engine block or cylinder head. Defect is where coolant pressure is higher than oil pressure.

Figure 2, Visual Inspections

Calendar Cycle Schedule

All generator manufacturers publish maintenance schedules broken down by a calendar schedule. Standard Maintenance Schedule is illustrated in (Table 1):


Emergency standby generator systems should have at least two maintenance events per year performed. Examples listed below:

  • Load Bank Testing – Generator is placed under load for a period of time using an external load bank tester.
  • Confidence Test – Generator is placed under load for a period of time using facility as a load.
  • Fluid Analysis – Lubricating oil, coolant and fuel analysis performed by laboratory.

Always follow manufacturer’s guidelines when performing maintenance, inspections and testing.

Operating Inspections

The application the generator is used in defines the inspections that need to be performed while in operation. Each application requires development of a different inspection. Basic inspections are provided in (Table 2):

Always consult manufacturer’s guidelines when designing inspections to be performed when the generator is operating. Consider recent repairs and add into inspection criteria.


When an emergency generator is removed from service for a permeate period of time it is placed in the layup status. Some basic steps to place a generator in layup can include:

  • Disconnect generator batteries.
  • Drain fuel system and change fuel filters.
  • Drain coolant and change coolant filters.
  • Replace air filters.
  • Insure all intake and exhaust ports are covered.
  • Disconnect all generator supply connections.

If shipping the generator all DOT regulations must be followed. Industrial shrink wrapping is offered by many companies and offers long term storage options (Figure 3).

Figure 3, Industrial Shrink Wrapping

Diesel Service and Supply & Planned Maintenance & Service Contracts:

Diesel Service & Supply has expanded our service options to provide On-Site Service Contracts for most of the larger generators that we sell. We also provide a variety of on-site services for customer owned generators within our immediate multi-state region. Contact our friendly staff today at 800-853-2703 for more details.


Figure 4, Remote Service Vehicles

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