Lawnmower and Oil (Please tell me no math is involved)

May 6, 2014 11:38 AM

I currently have 3 gas cans in my garage that may or may not have been mixed with oil. I know one of them has because I know my leaf blower requires it. I know one doesn't because my lawnmower takes straight gas. My challenge is I don't know which is which. Does anybody have an recommendations for how to solve my problem?

I've considered just mixing them all together and adding more oil and using it in the leaf blower but Im unsure of how exact the proportions need to be. (I've always just eyeballed it. Probably not the best, I know.) I would like to avoid just disposing of them properly but if thats best, I can.

posted by blackjack514 to Home & Garden (11 answers total)

Wouldn't you be able to see the separate layers if you were to pour the contents of each jar into a (separate, disposable) jar of water? We know that oil floats, and gasoline is also lighter than water.
posted by mudpuppie at 11:49 AM on May 6, 2014

Does the gas in the cans look any different? Unmixed gas should look slightly greenish yellow. It's been a while since I've had a two cycle engine, but I imagine that oil would discolor the gas slightly when mixed.

Failing that -- gas cans are cheap enough that I'd just buy two new ones and chalk the loss of the gas to a lesson learned.

What I suggest is either to use a different size for my 2-cycle gas/oil mix, and/or mark that can with a big "2" (or some other obvious indication like "GAS/OIL MIX") in permanent marker.
posted by tckma at 11:50 AM on May 6, 2014

Gasoline density vs motor oil density seems to indicate that gas is not as dense as motor oil. My suggestion would be to pour an equal volume of each can [say, 500mL] into a cup and measure the weight of each one, the one[s] with less weight have more gasoline, the ones with more have more oil. If you weren't particularly frightened by the math, you could calculate the density of each sample and then compare against the densities listed in the links above.
posted by jangie at 11:52 AM on May 6, 2014

Best answer: I was going to suggest weighing and comparing the densities, but it looks like two-stroke oil isn't that much denser than gasoline and if your gas:oil ratio is high you're going to need a fairly accurate scale to see any difference.

Is your oil dyed blue? If so, I think your best bet is going to be a color comparison. Bring your samples into a sunny area (but not direct sunlight) and compare is against a piece of white paper.
posted by backseatpilot at 11:56 AM on May 6, 2014

the gas mixed with two stroke oil should be dark blue-ish in color, vs amber/clear/yellowish/pinkish for straight gas.
posted by k5.user at 11:58 AM on May 6, 2014

Best answer: There's not enough oil to foul a 4-stroke engine, but you definitely don't want to run a 2-stroke without oil. You should be safe by mixing all three together, then setting aside one gallon and labeling it 2-stroke. You will then add a 50:1 shot of oil to that can. That will end up being more than 50:1, but aside from a little extra smoke it will be fine in the leaf blower. The other two can be used in a 4-stroke without harm.
posted by Gungho at 1:01 PM on May 6, 2014 [1 favorite]

Y'all should clarify two-stroke vs four-stroke, specifically which requires oil in the fuel and which is for lawnmower vs leafblower. It's obvious to us gearheads, but ... (sorry, not enough time right now for me to explain it myself)
posted by intermod at 1:31 PM on May 6, 2014

Gasoline is volatile. Oil is not. Pour a little bit out of each can onto a separate saucer and leave them out in the open for a week, and then look to see what kind of residue each one leaves.

Pure gasoline shouldn't leave much if anything. Gas mixed with oil should leave oil behind.

(Use a turkey baster.)
posted by Chocolate Pickle at 2:32 PM on May 6, 2014 [1 favorite]

Just pour it all in your car's tank and then fill the rest of the tank. That little bit of 2-stroke oil won't make a bit of difference. Then start from scratch.
posted by humboldt32 at 4:22 PM on May 6, 2014 [1 favorite]

I wouldn't be using oil-mixed gas in anything with a catalytic converter (such as a car). Probably it's not enough to matter, but catalysts are expensive and I wouldn't take the risk.
posted by How much is that froggie in the window at 11:24 PM on May 6, 2014

Gasoline is volatile. Oil is not. Pour a little bit out of each can onto a separate saucer and leave them out in the open for a week, and then look to see what kind of residue each one leaves.

That's the test I'd use too, but saucers are slow. Dip a rag in each and hang the rags up in the sun and the breeze for ten minutes. The one that still feels greasy is the one that got dipped in the oily fuel.
posted by flabdablet at 12:09 PM on May 7, 2014