Leaving a petrol generator to sit for six months or more is where most owners quietly ruin theirs. The damage rarely happens while it runs. It happens in the shed, when fuel turns to sticky varnish, and the rubber seals inside the carburettor shrink, harden, and crack. The twist is that draining the tank bone dry, the advice on half the forums, can do as much harm as leaving stale petrol in it.
The smarter approach to petrol generator storage is to keep the fuel system lubricated, not empty. At Outbax, we handle generators every day, and we see the same two failures again and again: a gummed carburettor from evaporated fuel, and perished seals from air drying. Here is how to store a petrol generator long term so it starts on the first pull next season, seals intact.
The Short Version
Here is what you need to know before storing your generator.
- Fill the tank and add a stabiliser for storage up to 12 months, rather than draining it dry.
- For storage beyond 12 months, drain the fuel and coat the internal seals with an oil that does not evaporate.
- Change the engine oil while warm, fog the cylinder, and set the valves closed before it sits.
- Protect the fuel cap gasket with a silicone protectant and cover the unit with breathable fabric, never plastic.
- Run the generator for about 15 minutes every three months to keep everything moving.
Why Generator Seals Dry Out, and Why Draining the Tank Is Not Enough
A petrol generator, such as the Gentrax GT800 Inverter Generator, carries two groups of vulnerable rubber: the seals that touch fuel, and the seals that touch air. Each fails for a different reason, so each needs a different fix.
When ordinary pump petrol sits still, its light fractions evaporate and leave a sticky varnish that clogs the tiny jets and passages inside the carburettor. Fuel blended with ethanol is worse again, because ethanol draws in moisture and separates over time.
Drain everything to dodge that, though, and you trade one problem for another. The float bowl gasket, the fuel lines, and the rubber-tipped needle valve are built to stay wet. Leave them in dry air for six to twelve months, and they shrink, go brittle and crack. That needle valve is usually a Viton elastomer, and elastomeric degradation is a common reason a stored unit floods or will not hold fuel. Add condensation in the fuel tank, and you have rust as well. So the goal is not dry or wet, but the right protection for how long the machine will sit.
Here’s what one of our customers said about the Gentrax GT800 Inverter Generator:
“Amazing product for my off grid property! It runs for over 8hrs and so quiet I can use it to watch tv late at night, charge laptops and batteries to run pumps and 12v lights. Really a gem!”
Carburettor and Fuel Line Seals: Should You Drain the Fuel or Leave the Tank Full?
The honest answer is that it depends on how long you are storing it.
The Wet Method (Best for Up to 12 Months)
For seasonal storage, keep it simple and keep it wet.
- Fill the fuel tank to the top so there is no air gap for condensation to form.
- Add a storage-grade fuel stabiliser such as Penrite Ultimate Fuel Stabiliser, dosed at the ratio on the bottle.
- Run the generator for 10 to 15 minutes so the treated fuel coats every jet, passage, and rubber part rather than raw pump fuel.
That is fuel stabiliser-treated wet storage, and for most owners packing a unit away over summer or winter, it is all you need.
The Drain and Lubricate Method (Best for 12 Months or More)
If the machine will sit for more than a year, or you would rather not leave petrol in it, drain it, but do not leave the internals bare.
- Empty the fuel tank into a clean container.
- Drain the carburettor using the float bowl drain screw on the underside of the bowl.
- Detach the fuel line at the carburettor and drop a few millilitres of pure silicone oil or automatic transmission fluid into the intake port.
- Pull the starter cord slowly a few times to spread the oil across the internal seals.
Silicone oil and ATF don’t evaporate or form varnish, so the float bowl gasket and needle valve stay supple for years.
Choosing a Stabiliser
A storage-grade stabiliser holds fuel stable for 12 to 24 months and guards against ethanol-related corrosion, which a cheap octane booster will not. If you buy one product for petrol generator storage, make it a quality stabiliser.
Protecting the Engine and Crankcase Seals
The fuel system gets most of the attention, but the engine has its own vulnerable rubber components, including the crankshaft oil seals, which acid can also damage.
Change the Oil While It Is Warm
Used engine oil contains corrosive combustion byproducts. Left in the sump for months, those acids attack the crankshaft oil seals from the inside, which is how crankshaft oil seal corrosion sets in. Run the engine to warm the oil, drain it, then refill to the base of the filler threads. Warm oil carries the contaminants out with it.
Fog the Cylinder Bore
Remove the spark plug and pour roughly 15 millilitres of clean motor oil, or a purpose-made fogging spray, into the plug hole. Slowly pull the cord two or three times to spread the film across the cylinder wall and piston rings. This layer of cylinder fogging oil gives anti-corrosion protection and keeps moisture off bare metal.
Set the Valves Closed
Pull the recoil handle slowly until you feel firm resistance, then stop and leave it there. That is the compression stroke, with both valves shut. Parking the engine on the compression stroke seals the combustion chamber off from outside air and humidity.
Quick Reference: Seal-by-Seal Storage
Here is the short version, mapped to each seal group and the method that protects it.
| Seal location | Main risk | Recommended method | Product or tool |
|---|---|---|---|
| Carburettor float bowl and jets | Varnish build-up or dry cracking | Stabilised fuel for up to 12 months, or silicone oil injection beyond that | Penrite Ultimate stabiliser; silicone oil or ATF |
| Fuel line and needle valve | Viton degradation, brittle rubber | Keep wet with treated fuel, or coat with oil once drained | Fuel stabiliser; pure silicone oil |
| Crankshaft and sump seals | Acid corrosion from used oil | Fresh oil change while warm, valves set closed | Clean engine oil; fogging oil |
| Cylinder bore and piston rings | Surface rust and moisture | Fog with 15ml oil, park on the compression stroke | Fogging spray or motor oil |
| Fuel cap gasket and outer trim | UV exposure and dry rot | Wipe with silicone protectant, store under a breathable cover | 303 Rubber Seal Protectant; canvas cover |
External Cap and Chassis Seals, and Where You Store It
The seals you can see are the easiest to protect and the easiest to forget.
Protect the Fuel Cap Gasket
Wipe a thin film of a dedicated rubber protectant, such as 303 Rubber Seal Protectant, or a little pure silicone grease, onto the fuel cap rubber ring and any exposed control panel boots. It keeps the fuel tank vapour cap sealing valve flexible so it still seals next season. Avoid petroleum jelly and heavy lithium greases, which can make some rubber swell and warp.
Store It Dry, Ventilated, and Covered Properly
Never wrap a generator in a plastic tarp. Nonporous plastic traps humidity underneath and speeds up rust and dry rot. Use a breathable canvas or fabric cover instead. In coastal parts of Australia, where salt air accelerates corrosion, a dry, ventilated shed matters even more than the cover.
Choosing a Generator That Is Easy to Store and Restart
Storage is far less painful on a machine built for it. Inverter models run cleaner and stay simpler to maintain, and a fuel tap and easy drain screw turn an afternoon job into a ten-minute one.
If you are shopping, Outbax stocks several units for owners who store them between uses. The Gentrax GTX4200 Pro Inverter Generator is a popular camping and caravan choice that spends much of the year in storage, and the Gentrax GT3500 Inverter Generator is a quiet mid-size alternative. For an easy quarterly start without a recoil cord, the Gentrax GTX3500 Inverter Generator makes the maintenance run painless, while the Gentrax GS2-7500IE Inverter Generator is sized to sit ready between outages.
One more option: if storage is the whole headache, a portable power station has no fuel and no seals to dry out, and for lighter needs it sidesteps the problem entirely.
Here’s what one of our customers said about the Gentrax GTX4200 Pro Inverter Generator:
“This is a great generator. I purchased it as a backup generator for my home during blackouts, but to also use if I need power for a caravan down the track. This generator starts easy and isn’t to loud. The delivery was swift, as was the customer service.”
Keep It Exercised
Even a well-prepared generator benefits from movement. A quarterly preventative exercise run, roughly 15 minutes every three months under a light load, keeps the seals coated, the battery charged on electric start models, and the carburettor clear. On units you keep drained between runs, finish with a deliberate dry run to fuel starvation, letting the carburettor run itself empty, so no petrol is left to varnish.
The Bottom Line
Good petrol generator storage comes down to one idea repeated across every seal: protect the rubber; don’t just empty the machine. Treat the fuel or lubricate the carburettor, change the oil warm, fog the cylinder, seal the valves, and shield the outer rubber, and your generator will wait quietly until you need it. When it is time to upgrade to something built for easy storage, browse the inverter and portable generator range at Outbax.
