What is pre-mix oil?

If you’re like me, the extent of your exposure to engine maintenance has basically revolved around the family car. The gas goes in the tank, the oil goes in the oil fill, air in the tires, blue window stuff goes in the window stuff thing… and anything else involves a mechanic…or my brother in law (who’s cheaper, provided he’s sober.)

But when we start to look at two and four cycle engines, things are a little different. Because, now we’re dealing with mixing fuel with oil in a certain percentage. Now, all of the sudden you have to pay attention to what you’re putting in the machine and that’s a pain.

And since we are genetically preconditioned to dislike change of any kind (I’m pretty sure it’s a scientificky fact!), some folks just refuse to deal with it. They’re leery of adding anything to their gasoline because of the possibility of screwing something up.

In fact, lots of folks avoid the whole mess by just going electric. Which is fine until a wire frays, or you drop the thing, or it gets wet and stops working. Suddenly you’re forced to face the harsh reality that no one ever intended for that thing to be repaired. So it’s off to the dumpster with ye! Awaaay with you beggar!

If you’re in that boat, then you’re going to kick yourself when you read this, because the whole pre-mix phenomenon is a lot simpler than you ever thought.

So let’s rob those two cycle engines of their power over you and learn a little about Gas / Oil mixture.

Here’s what we already know
Your engine needs oil for those rapidly moving internal parts. Oil reduces friction, regulates temperature and helps to prevent the engine from seizing up. No surprise there.

We be strokin’

In a four-stroke engine (like your lawn mower engine, for example), you pour the oil directly into the oil fill, where it pools at the bottom of the engine. As the engine runs, the parts inside simply splash the oil all over the place or your engine may have an oil pump, which picks up the oil and distributes it to the appropriate places.

In a two stoke engine (chainsaws, mini-tillers, and/or many trimmers respectively), there is no oil reservoir, but the engine still needs lubricant.

Two-stroke engines employ what’s called a “total-loss lubrication system”, meaning that the oil (which is mixed with the gasoline) is depleted as the gasoline is depleted. When the gas is gone, the oil is gone and must be replenished with each re-fueling.

I know what you’re wondering.

“So what would happen if I ran it without the oil?”

Disaster. Quick, expensive, disastrous disaster. Running straight gasoline in a two cycle engine is the quickest route to a destroyed two cycle engine.

It will start. I will run (boy, will it run), then it will seize and die and then it’s time to go buy a new saw, or trimmer, or whatever. We’ll leave the light on for you.

How much is too much?

Mixture ratios vary by manufacturer.

Many newer 2-cycle engines use a 50:1 ratio, while some older engines call for 40:1 or 32:1. When in doubt, refer to your owners manual or the manufacturer.

If you have trouble calculating your ratio, here is a handy 2-Cycle Oil Mix Chart.

If you still aren’t sure of your mixture ratio, or you just don’t want to mess with it, consider using OPTI-2 TWO CYCLE OIL MIX. Opti comes in pre-measured pouches and mixes with either 1 or 2 1/2 gallons of fuel. Ask your local dealer about Opti-2.

Let’s recap.

Pre-Mix oil mixes with the gasoline in your two cycle engine. Know your mixture ratio and check your oil level on a regular basis and you should be OK.

There you go…a little about mixing oil with gasoline for your two cycle engine.

Pretty slick, huh? HA!


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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.