Maintenance
Generator Maintenance Checklist: Oil, Filters, Fuel and Storage
A generator is the one tool that is expected to work perfectly after sitting idle for weeks. That is precisely why so many fail at the moment they are needed. Stale fuel, a flat battery, a clogged air filter and black oil are behind most of the generators that will not start during an outage. None of these need a mechanic. This checklist sets out what to do after every use, every month and every year, for the small petrol sets used in homes and shops and for the diesel sets used in workshops, so that your generator starts first pull or first turn of the key.
In this guide
Engine oil: the single most important job
Small generators carry very little oil, often well under a litre, and the engine runs hot and hard. That small quantity breaks down quickly. Dirty oil is the leading cause of early engine wear on generators, and a low level is the leading cause of sudden engine death, because a set run dry seizes in minutes.
Check the level before every run with the generator on level ground and the engine cold. Top up to the mark on the dipstick, never above it. Change the oil after the first few hours of a new generator's life, because the running in period leaves fine metal in the oil, and then at the interval the manual gives, which for most small petrol sets is roughly every 50 to 100 hours of running. If you cannot remember the last change, change it.
Use the grade the manual specifies, which for most small air cooled engines in Kenya's climate is a 10W-30 or 15W-40 four stroke engine oil. Do not use two stroke mix in a four stroke engine. Drain the old oil warm so it flows out fully, and dispose of it responsibly rather than pouring it on the ground.
- Check the level before every start, on level ground
- First change after the running in period, then every 50 to 100 hours
- Use the grade in the manual, never overfill
- Many sets have a low oil shutdown: if it will not start, check oil first
Air filter: cleaning and replacement
Generators live in dusty places, on verandas, in sheds and on building sites. The air filter stops that dust reaching the engine, and as it fills up the engine gets less air, runs rich, loses power and uses more fuel. Black smoke and difficulty starting are the usual signs.
Foam filters can be washed in warm soapy water, squeezed dry, lightly oiled with clean engine oil and squeezed again to remove the excess. Paper filters are tapped clean or replaced, never washed. Check the filter monthly if the set runs regularly, and every time after a dusty job. Never run the engine without the filter fitted, even for a minute, because an unfiltered engine wears out fast.
Fuel: the cause of most no start problems
Petrol goes stale. After a month or two in the tank it starts to form gum that blocks the carburettor jets, and a blocked jet means the engine will crank but not fire, or will start and then die. This is the single most common fault on standby generators that only run during outages.
The answer is to run the generator for fifteen to twenty minutes every two to four weeks under some load, which keeps fresh fuel moving through the carburettor and charges the battery on electric start sets. If the set will stand for more than a month, either run the carburettor dry by closing the fuel tap and letting the engine stop, or drain the tank and carburettor bowl. Store fuel in a sealed container in the shade and use it within a few weeks.
Diesel keeps better than petrol but it attracts water and grows bacteria in the tank if left for months, which clogs the fuel filter. Keep diesel tanks full to reduce condensation, drain the water separator if the set has one, and change the fuel filter at the interval in the manual. Buy fuel from a busy station where it turns over quickly.
- Run the set under load for 15 to 20 minutes every 2 to 4 weeks
- For storage over a month, run the carburettor dry or drain it
- Keep diesel tanks full and drain any water separator
- Replace the fuel filter at the manual's interval
Spark plug, valves and the recoil starter
On petrol sets, remove the spark plug once or twice a year. A tan coloured tip is healthy. Black and sooty means the engine is running rich, usually a dirty air filter. White and blistered means it is running hot or lean. Clean the electrode with a wire brush, check the gap against the manual and refit it snugly, not over tight. Replace the plug if the electrode is worn rounded.
If the pull cord is getting harder to pull or does not return, the recoil mechanism needs cleaning and a light oiling, which is a simple job before the cord snaps. On sets that have done hundreds of hours, valve clearance checks are worth having done by a technician, because tight valves cause hard starting and loss of compression.
Electric start sets: battery care
Key start generators depend on a small lead acid battery, and a flat battery is the most common reason a key start set fails to start. The battery charges only while the engine runs, so a set that sits for weeks drains it. Monthly running keeps it topped up. If the set stands longer, charge the battery with a separate charger or disconnect it.
Keep the terminals clean and tight, because corroded terminals stop the starter even on a charged battery. Most key start sets also have a recoil cord as a backup. Try it if the starter only clicks, and then deal with the battery once the lights are back on.
Load, cooling and cables
Running a generator at its full rated load for long periods shortens its life, and running it with almost no load for hours is also bad for diesel engines, which glaze their cylinder bores when under worked. Aim for the middle of the range. If a set is routinely at its limit, the right fix is a larger generator, not a longer run.
Keep the cooling fins and the area around the engine clear of dust and leaves, and give the set space on all sides. Never run it in an enclosed room or a garage with the door shut, because exhaust gas kills quietly. Check the output cable and plugs for cuts and heat damage, and keep connections dry. A generator sitting on a damp floor with a frayed lead is an electrical hazard as well as a fire risk.
A simple schedule to stick to
Before every run: check the oil level, check the fuel, look for leaks, make sure the air filter is in place and the vents are clear. After every run: let it cool, wipe it down, close the fuel tap if it will stand for a while.
Every month: run under load for fifteen to twenty minutes, check the air filter, check the battery terminals on electric start sets. Every three months or 50 hours: change the oil, clean or replace the air filter. Every year or 100 to 200 hours: new spark plug, fuel filter, valve clearance check, inspect the recoil starter and the cables.
Write the hours and the date of each oil change on a strip of masking tape on the generator frame. It takes ten seconds and it ends the guessing. ToolHub Kenya stocks key start and recoil start petrol generators from 1 kVA up to 4 kVA and a 3 kW diesel set. If you are not sure which size suits your home or shop, read our generator sizing guide or ask us on WhatsApp.
- Before every run: oil, fuel, filter, vents
- Monthly: run under load, check filter and battery
- Every 3 months or 50 hours: oil change, filter service
- Yearly: plug, fuel filter, valves, cables, recoil starter
Tools mentioned in this guide
Prices change with stock and supplier costs, so we quote on WhatsApp. Send us the tool and your town for today's price and availability.
Frequently asked questions
My generator cranks but will not start. What should I check first?
Check the oil level first, because many sets have a low oil cut out. Then check for stale fuel, a closed fuel tap, a choke not set, and a dirty spark plug. Stale petrol blocking the carburettor is the most common cause on sets that stand for weeks.
How often should I change the oil in a small petrol generator?
After the first few hours on a new set, then roughly every 50 to 100 hours of running or every three months, whichever comes first. Follow the interval and oil grade in the manual for your model.
How long can petrol stay in the tank?
Petrol starts to deteriorate after a month or two. If the set will stand longer than that, run the carburettor dry or drain the tank and bowl, and refill with fresh fuel before the next use.
Is it bad to run a generator with very little load?
For diesel sets, long periods at very low load cause bore glazing and wet stacking. Petrol sets tolerate it better but still waste fuel. Try to run any generator in the middle of its rated range.
Why does my key start generator only click?
The battery is flat or the terminals are corroded. Charge or replace the battery and clean the terminals. Most key start sets also have a recoil cord as a backup for the moment you need power.
Can I run the generator inside the shop if the window is open?
No. Exhaust gas contains carbon monoxide, which builds up indoors even with a window open. Run the set outside, away from doors and windows, with the exhaust pointing away from the building.
