Pre-Mix Fuel

Pre-mix fuel is an ethanol-free blend of high-octane gasoline and synthetic two-stroke oil, mixed at the factory to a precise ratio so you never have to measure oil into a gas can again. Most people use pump gas in their expensive outdoor power equipment, assuming that if it’s good enough for their car, it’s good enough for their hedge trimmer, string trimmer, or chainsaw — and unfortunately, that’s the worst thing you could do unless you like spending money on repairs. Pre-mix solves that. It’s for anyone running a chainsaw, trimmer, or blower who wants the thing to start on the second pull after sitting in the garage all winter.

Here’s the core problem it fixes. The majority of pump gas contains ethanol, which absorbs water as it sits in the tank. Water promotes corrosion that eats away vital components, ethanol can damage plastic and rubber fuel-system parts, and pump gas degrades fast and forms gums — causing equipment to run less efficiently and, worse, to fail. That matters more in Montana than most places. Seasonal equipment sits idle for months — snow blowers all summer, chainsaws and trimmers all winter — and ethanol gas turns sour during those long stretches. Pre-mix doesn’t.

The stability numbers back it up. Season after season, pre-mix delivers quick, reliable starts and peak performance. Across brands, it lasts roughly two years opened and up to five years unopened — which is exactly what you want for firewood-season chainsaw fuel or a snow blower that won’t see action until December.

Western Building Center carries a 50:1 ethanol-free premix in a one-gallon size.

Matching the Ratio to Your Engine

This is the whole ballgame. Run the wrong ratio and you’ll foul a plug or, worse, cook a piston. The two common ones are 50:1 and 40:1. Consult your owner’s manual to determine the pre-mix ratio needed — that’s not boilerplate, it’s the one step that protects the engine.

The ratio sorts out cleanly by brand. A 50:1 ratio covers Craftsman, Redmax, Echo, Ryobi, Homelite, Shindaiwa, Husqvarna, Stihl, Maruyama, and Toro. A 40:1 ratio covers Bolens, Craftsman, McCulloch, Poulan, Troy-Bilt, Weed Eaters, and Yard Machines. Note Craftsman shows up on both lists — another reason to check the manual rather than guess.

Octane runs high across the board. STP’s pre-mix uses 93-octane ethanol-free fuel. VP’s 50:1 is 94 octane. Husqvarna XP+ runs 95-octane ethanol-free fuel mixed with their synthetic oil blend.

There’s also a four-cycle version for engines that run straight gas. It’s made for small 4-cycle engines that use separate gas and oil — generators, lawnmowers, snow blowers, and power washers. Don’t pour a 2-cycle mix into a 4-cycle engine or vice versa.

Spec	Detail
Common ratios	50:1, 40:1, plus 4-cycle
Octane range	92–95, ethanol-free
Oil certifications	JASO FD, ISO-L-EGD, API TC
Shelf life (sealed)	Up to 5 years
Shelf life (opened/in-tank)	~2 years
Common sizes	1 quart, 1 gallon, 2.5-gal pail, 5-gal pail

Those oil certifications tell you the lubricant package is legitimate. STP is formulated to meet or exceed OEM standards with JASO FD and ISO-L-EGD certified oil. VP meets or exceeds JASO FD, ISO-L-EGD, and API TC.

How to Use It and Store It

Dead simple. It’s ready to use — consult the owner’s manual, and do not overfill. No measuring, no mixing bottle, no doing math on the side of a can.

Storage is where Montana gear lives or dies. Keep cans in a cool, dry spot out of direct sunlight, and before pouring fuel that’s been sitting, give it a look and a sniff — separation or a sour smell means it’s done. The ethanol-free formulation is what makes the long sit possible. Unlike pump gas, this fuel prevents gum-like buildup and fuel-line degradation, and it’s designed to maximize freshness and won’t lose stability like fuel straight from the pump.

One bonus worth knowing for warranty-conscious buyers. Some brands stand behind their formulation by doubling the limited warranty when you include their premix with a power tool purchase, and the no-ethanol blend maintains stability for up to two years after the seal is broken. Read the fine print — that kind of double-warranty protection typically applies to products purchased for personal, non-income-producing household use.

Frequently Asked Questions

Why not just run pump gas? Pump gas usually contains ethanol, which absorbs water as it sits in the tank. That water promotes corrosion that eats vital components, ethanol damages plastic and rubber fuel-system parts, and pump gas degrades fast and forms gums — making equipment run poorly or fail outright.

How long does pre-mix last in storage? It lasts about two years opened and up to five years unopened. For seasonal equipment that sits idle for months, that stability is the main reason to use it.

What’s the difference between 50:1 and 40:1? It’s the fuel-to-oil ratio your engine was built for. 50:1 fits brands like Echo, Husqvarna, Stihl, Ryobi, and Toro, while 40:1 fits Bolens, Poulan, Troy-Bilt, and McCulloch, among others. Always consult the owner’s manual to determine the ratio.

Can I use pre-mix in a four-cycle engine? There’s a dedicated four-cycle product for that. The pre-mix line is recommended for high-revving 2- and 4-cycle engines, with 4-cycle formulas compatible with all 4-cycle equipment. Match the product to the engine type — don’t substitute.

What equipment takes pre-mix? It’s engineered for outdoor power equipment including pressure washers, generators, leaf blowers, chainsaws, string trimmers, mowers, edgers, pole saws, snow blowers, and hedge trimmers — covering the 2-cycle tools that need a gas/oil mix and the 4-cycle ones that run separate.

Does the oil quality actually matter? Yes. Look for the certifications. Pre-mix is precision-engineered with synthetic lubricants and advanced stabilizers, and labels marked JASO FD, ISO-L-EGD, or API TC tell you the oil package meets recognized performance standards.