Generator Oil and Fuel Filters: How Often to Change

Generator oil and fuel filters are the least glamorous parts we sell and the ones that prevent the most expensive failures. A filter costs a fraction of what a set of bearings costs, and skipping one is how you end up needing the other.

The complication with a standby set is that the usual advice — change every X hours — does not fit, because a standby generator might run twenty hours in a year. Time matters as much as hours.

A realistic interval for generator oil and fuel filters

For a standby set that runs on test and during outages, plan on annually or at the engine maker’s hour figure, whichever comes first. For a prime-power set that works for a living, follow the hours and do not stretch them.

The reason time matters is condensation and fuel degradation. Diesel sitting in a tank for a year picks up water and grows organisms; the filter catches the result, and a filter that has been catching it for two years is not catching much any more.

Do not skip the water separator

South African diesel varies, and bulk tanks that are topped up irregularly collect water. A fuel system component like a water separator is doing a different job from the main filter, and draining it is a five-minute check that belongs on every service sheet.

If you have seen the set stumble under load, or the fuel filter bowl looks cloudy, that is water rather than dirt and no amount of filter changes alone will fix the tank.

While you have the covers off

A service is the cheapest time to deal with anything else that is marginal, because the labour is already being spent. Worth a look:

The cooling system components and hoses — see generator water pump and cooling care for what to check. The belt tensioners, which are cheap and quietly destroy belts when they are tired. And the sensors, which nobody thinks about until one shuts the set down.

Finding the right filter

Filters are one of the areas where part numbers matter most, because physically similar filters have very different micron ratings and bypass valves. Read the number off the old one and put it into the part finder rather than matching by eye.

With 8,449 parts in the finder we carry a great deal more than the oil filter and fuel filter category pages show, so search before you conclude we do not have it. Stuck? Send us the number.

The economics

A full filter service is a small fraction of the cost of a big end bearing set and the labour to fit it. Oil and fuel filters are not where to save money on a generator — they are what stops you spending it somewhere far worse. If you want the wider maintenance picture, start with our guide to a healthy generator.