It Ran in October and Won't Start in April
The mower, generator or snow blower was stored running and will not start in spring, and the fuel that sat in it all winter is the first suspect
The short answer
This page sells prevention, and it says so in the box because the order matters. Fuel stabilizer keeps fresh fuel fresh. It does not restore fuel that has already gone stale, and tipping it into a tank of dead fuel in April does nothing but season the problem. So the spring half of this page is a triage: a machine that will not start after storage gets its fuel drained, its plug and filter checked, and its carburettor suspected in that order, and no bottle is the fix for it. The autumn half is the product: fresh fuel, treated at the maker dose and run through the machine for a few minutes before storage, keeps for up to 12 months. STA-BIL 360 Protection holds 4.9 stars from 96 reviews at Harbor Freight (November 2026), with every reviewer recommending it. That count is modest and it is printed as modest wherever the score appears on this page. The habit is the verdict: treat the fuel in October and April stops being a diagnosis.
Why does this happen?
Gasoline is a blend that ages. Its lightest parts evaporate first, and what is left oxidises and thickens into gum and varnish. In a tank that means fuel an engine cannot burn well. In a carburettor, where fuel sits in small passages and a shallow bowl, it means varnish across jets a hair wide, and an engine that turns over, coughs, and will not catch, or catches and hunts. Three to six months of storage is enough. The machine was stored running, and time in the tank is what changed.
Ethanol blend fuel makes the clock faster. The ethanol in ordinary pump fuel draws water out of the air in the tank, and past a point the water and ethanol drop out of the fuel as a separate layer that sits at the bottom, where the fuel pickup drinks from. That layer does not burn, and it corrodes the metal it rests against. A stabilizer's job is to slow the oxidation, take up the water before it separates, and leave protection on the fuel system surfaces, which is work it can only do in fuel that is still fresh.
That timing is the page's whole shape. The autumn search, how to store a mower for winter, is the product door, because autumn is when fresh fuel, a dose, and five minutes of running can still change April. The spring search lands on the same page and gets the honest triage first. A seller who put the bottle at the top of the spring answer would be selling you a treatment for a tank that needs draining, and the drained tank would still need its carburettor cleaned if the varnish has set.
The fix, in order
Work down the list: free and cheap steps first. Stop when the plant turns the corner; the product is only for what the free steps cannot do.
Free step
Spring triage: drain, refill, then plug and filter
Drain the stored fuel, refill with fresh fuel from a clean can, and try the start. If it catches, run it ten minutes and you are done. If not, pull the spark plug: a plug wet with fuel points at flooding or a fouled plug, a dry plug points at fuel not arriving. Check the air filter for a clogged, oil-soaked element. A machine still dead after fuel, plug and filter is a carburettor job, at a bench or a shop, and it is better to know that in an hour than after a shelf of additives.
The product step
Autumn: treat fresh fuel and run it through
At the season's last use, dose fresh fuel in the can at the maker's measure, fill the machine, and run it for five minutes so treated fuel reaches the carburettor bowl, which is where stale fuel does its damage. Top the tank up to limit the air in it, or drain the machine fully if its maker directs that instead for long storage. The bottle is STA-BIL 360 Protection, 4 ounces treating up to 16 gallons, so one bottle covers the mower, the generator and the snow blower with room to spare.
The product for this step
STA-BIL 360 Protection Ethanol Fuel Treatment & Stabilizer, 4 fl. oz.
Habit step
Date the bottle and the can
Write the month on the fuel can and on the stabilizer bottle with a marker. Treated fuel keeps up to 12 months and an opened bottle keeps its strength about 2 years by the maker's own guidance, and both clocks are invisible without a date on the container. Next autumn's decision gets easy: fresh can, in-date bottle, dose, run, store.
The evidence, in tiers
Tier 1 · The method
The method follows the maker's storage directions and the fuel ageing mechanism: stabilizer dosed into fresh fuel only, treated fuel run into the carburettor before storage, tank topped to cut the air volume, and the 12 month treated life and 2 year opened bottle life stated as the maker states them. The spring triage follows the failure order the mechanism produces: fuel first, then spark, then air, then the carburettor.
Tier 2 · This product
STA-BIL 360 Protection holds 4.9 stars from 96 reviews at Harbor Freight (November 2026), with 100 percent of reviewers recommending it. The star spread on the same page runs 90 five-star reviews against a single two-star, so the average is broad agreement on a small base. That count is modest next to the records on this site's other shelves, and it is printed as modest: the score is strong, the base is 96 owners, and the class's far larger record sits on a storefront this page does not use as proof. That record is the retailer's own, read for this guide. No fuel was treated for this guide.
The modest count is handled the way this site handles thin records: printed wherever the score appears, never rounded up into a reputation the number cannot carry. The mechanism evidence does the heavy lifting on this page: fuel ageing and ethanol water uptake are the maker's own account of what the product prevents, and the prevention claim is the narrow one the record supports.
Tier 3 · What owners report
Owners describe machines stored on treated fuel starting in spring without the drain and clean ritual, generators kept ready across seasons, and older machines running better on treated fuel. Reports are strong and short on complaints; the single low score in the spread is the record's only real dissent. Nothing in the owner record claims the product revived fuel that had already gone stale, which matches the limit this page prints in its verdict.
The alternatives, conceded where they win
| Option | What it is | The honest verdict |
|---|---|---|
| STA-BIL 360 Protection, 4 fl. oz. | A measured dose for fresh fuel at storage time: stabilises, takes up water, protects against ethanol damage, up to 12 months | The pick: the honest prevention claim, a strong score on a disclosed modest count, and a bottle sized to treat a whole shed's fuel at a small price. |
| STA-BIL Storage | The same maker's long-storage form, rated by its maker for up to 24 months in storage | The long-storage row, for machines that sit a year or more between uses. Named here with no score: its large owner record sits on a storefront this page does not use as proof, and no first-party record for it was settled for this guide. Buy it on the maker's 24 month claim if your storage runs that long, knowing the claim is the maker's. |
| Drain the tank and run the carburettor dry | The free method: empty the tank, run the engine until it stops, store it dry | The free row, and a sound one for the longest storage, with its caveat printed: a dry carburettor's seals and gaskets can dry and crack over a long sit, and a machine run dry still holds a spoonful of fuel in its bowl unless the bowl is drained too. Owners who store for six months or less usually find treated fuel the easier habit to keep. |
| Fuel additives poured into stale fuel in spring | Treatment bottles sold as restoring old fuel and fixing a no-start | Named not an option. Stale fuel is a chemical change already finished; an additive cannot un-oxidise it. The spring fix is the triage in this page's ladder: drain, fresh fuel, plug, filter, carburettor. Money spent here is the drain and refill you still have to do, plus the bottle. |
The honest price comparison
The bottle costs less than a single small-engine shop visit's first half hour, treats up to 16 gallons, and one bottle covers a shed of machines for a season or two. The comparison is against the spring alternative: a drained tank at best, a carburettor clean at worst, and a machine out of action on the first weekend it is needed. Prevention at this price is not a close call. What the money cannot buy is last autumn back, which is why the spring half of this page is a triage and not a sales pitch.
Where it falls short
These weaknesses come from the product's own reviews, not from a rival's marketing. Read them before you buy.
- It cannot help fuel that has already gone stale. That is the product's limit and this page's first rule. Spring no-starts get the triage, not the bottle.
- The count behind the score is modest. 96 reviews is a small base, printed wherever the 4.9 appears on this page. Owners agree strongly; there are not many of them on this record.
- Treated fuel still has a life. The maker rates treated fuel at up to 12 months. A machine stored two years on treated fuel can still meet you with a dead tank, and the can and bottle dates in the ladder are what keep that surprise away.
- An opened bottle ages too. The maker's guidance gives an opened bottle about 2 years of strength. Last decade's half bottle on the shelf is not this product any more, whatever the label says.
The product, in short
STA-BIL 360 Protection Ethanol Fuel Treatment & Stabilizer, 4 fl. oz.
Questions people ask next
My mower will not start right now. Will this fix it?
No, and any page that tells you otherwise is selling you a bottle for a draining job. Work the triage: drain the stale fuel, refill fresh, then plug and filter, then the carburettor. Buy the stabilizer with the fresh fuel, for the storage that starts this autumn.
How much do I use?
At the maker's measure on the bottle: the 4 ounce bottle treats up to 16 gallons, which works out to a small dose per gallon. Dose the can, not the machine's tank, so every fill from that can is treated, and run the machine a few minutes after filling so treated fuel reaches the carburettor.
Is treated fuel or a drained tank better for storage?
For a season, treated fuel is the easier habit and protects the carburettor's insides while it sits. For storage past a year, draining fully, bowl included, is the surer route, accepting that seals can dry over long dry storage. The honest answer depends on the length of the sit, which is why both rows are in the comparison.
Does it work in two-stroke fuel?
The mechanism is the same and the need is sharper, because two-stroke fuel sits in small cans for trimmers and saws and ages between uses. Dose the two-stroke can when you mix it, date the can, and the trimmer's spring start gets the same help as the mower's.
Harbor Freight listing record for STA-BIL 360 Protection Ethanol Fuel Treatment & Stabilizer, 4 fl. oz., SKU 62602 (November 2026) · Maker directions and guidance for STA-BIL 360: dose rate, 12 month treated fuel life, 2 year opened bottle life · Small engine storage practice: drain and refill triage for stale fuel no-starts
The Fix JournalCase 39Plants & Garden