How to Store a Generator So It Starts When You Need It
A generator is unlike every other engine you own. A mower gets used weekly through summer. A generator might sit untouched for eighteen months and then be expected to start first pull, in the dark, in bad weather, when the power has just gone out.
That is a demanding requirement, and it is why so many generators fail at exactly the wrong moment. The failure did not happen during the outage. It happened slowly, in a garage, over the preceding year.
Understand What Kills a Stored Generator
An engine generator combines a small petrol engine with an alternator, and the failure modes come almost entirely from the engine side.
Three things account for the overwhelming majority of no start situations after storage. Stale fuel that has gummed the carburettor, a battery that has discharged and sulphated, and surface corrosion inside the cylinder. All three are preventable, and none of the prevention is difficult.
Deal With the Fuel Situation
The mechanism is the same one that affects mowers, which we covered in detail in what ethanol fuel actually does to a small engine. Ethanol pulls water from the air, the mixture separates, and the residue blocks jets narrower than a hair.
The difference is the storage period. A mower sits for six months. A generator often sits for two years, which makes the choice more consequential.
- Preferred, run it completely dry. Close the fuel tap, let the engine run until it stops, then drain the carburettor bowl using the drain screw underneath it. Most generators have one
- Acceptable, treat and fill. Fill with fresh fuel, add stabiliser at the correct dose, then run the engine for ten minutes so treated fuel reaches the carburettor rather than just sitting in the tank
Change the Oil Before It Goes Away
Same principle as any small engine. Used oil is contaminated and mildly acidic, and two years is a long time for that to sit against bearing surfaces.
Generators often use a slightly different grade to mowers, because they are more likely to be started in cold conditions. A multigrade such as 10W30 is usually the better choice for that reason, and the full reasoning is in our guide to choosing the right oil for your small engine.
Protect the Cylinder
Over a long storage period the oil film on the cylinder wall drains away and leaves bare metal exposed to whatever moisture is in the air.
Remove the spark plug, add about a teaspoon of clean engine oil into the cylinder, and pull the recoil slowly several times to distribute it. Then pull slowly until you feel resistance and stop there. That position closes both valves, which seals the combustion chamber against humid air for the whole storage period.
Fit a fresh plug before you put it away rather than after, so that when you need the machine there is one less thing to think about.
Look After the Battery
This is the single most common reason an electric start generator fails during an outage, and it is entirely avoidable.
| Storage approach | What happens |
|---|---|
| Battery left connected, no charger | Discharges over weeks, sulphates, dead within a year |
| Battery disconnected, no charger | Discharges slowly, may survive one season |
| Battery on a maintainer | Stays healthy for years |
| Battery removed and kept frost free on a maintainer | Best case |
A trickle charger costs less than a replacement battery and considerably less than discovering the problem during a storm.
Run It Every Few Months
This is the step that separates generators that work from generators that do not, and it is the one people skip.
Every three months, start the machine and run it for around twenty minutes with a real load connected. Not idling, and not unloaded. A couple of work lights or a heater gives the alternator something to do and brings the whole machine up to temperature.
This circulates oil, drives moisture out of the engine and the windings, keeps the carburettor wet, and most importantly tells you the machine works while you still have mains power to sort out any problem. Put it in your calendar, because the whole point is that nothing else will remind you.
If you have chosen the dry storage route, run this exercise on a small amount of fresh fuel and drain it again afterwards.
Store It Somewhere Sensible
Dry, ventilated, off bare concrete and out of direct sun. Concrete wicks moisture upward, so a pallet or a rubber mat underneath is worth the trouble.
Cover it with something breathable. A sealed plastic sheet traps condensation against the metal and does more harm than leaving it uncovered.
One safety point that is worth stating plainly because people do get this wrong. A generator produces carbon monoxide, which is colourless and odourless. Store it in a garage if you like, but never run it in one, and never in a shed, a porch, a basement or under an open window. Outdoors only, well away from doors and vents, every single time, including during the twenty minute test run.
The Routine on One Page
- Every three months. Run for twenty minutes under load
- Annually. Change the oil, fit a new spark plug, clean or replace the air filter
- Before long storage. Drain fuel including the carburettor bowl, fog the cylinder, remove the battery to a maintainer
- Always. Run outdoors, never inside any enclosed space
None of it takes long, and the payoff is a machine that starts on the night it matters. The same underlying habits apply across every small engine you own, and the seasonal version for garden equipment is in our guide on how to winterize a lawn mower.
Frequently Asked Questions
How often should I start my generator in storage?
Every three months, running it for around twenty minutes with a real load connected rather than idling. This circulates oil, drives moisture out of the windings and confirms the machine works while you still have mains power available to fix anything.
Should I drain the fuel from my generator before storing it?
For storage longer than a few months, yes. Run the engine dry with the fuel tap closed and also drain the carburettor bowl using the screw underneath it, since the bowl is where varnish deposits actually form. For shorter periods, fresh fuel with stabiliser is acceptable.
Can I store a generator in my garage?
Storing one in a garage is fine provided it is dry and ventilated. Running one in a garage is not, under any circumstances. Generators produce carbon monoxide, which is colourless and odourless, so they must only ever be run outdoors well away from doors, windows and vents.