Can I tell if oil has already been added to gasoline?
May 31, 2010 11:22 AM   Subscribe

Is there a way to tell if I have already added the oil into the gas can for my two-stroke trimmer?

Breaking out my the Stihl trimmer for the season and I found a 2 gallon gas container, full - sweet! But I realize I have no idea if I have already added the oil to the mix. (My gut says probably not, but then I was surprised to find a full gas can in my garage.)

Is there some distinctive odor or appearance that will indicate whether the gas in this container has already had oil added?

My gut instinct is that it's almost certainly better to run it with too much oil than too little. If I add another premeasured container, I potentially make a 50:1 mix into a 25:1 mix, with the caveat that but 25:1 is far better than 0:1. But is too much oil just as disastrous as too little?

In that case, maybe it's best to not assume anything and start from scratch - $300 trimmer vs. $6 worth of gasoline... (Say, did I just answer my own question?)

If that's the case, then my followup question is, how do I dispose of the gasoline currently in the can in order to refill and add new oil?
posted by BleachBypass to Home & Garden (11 answers total)
If you transfer it to a transparent container and let it sit, the oil will form a darker layer on the bottom after a while. This is why you're suppposed to shake it up before putting it in the gas tank of the engine.
posted by werkzeuger at 11:27 AM on May 31, 2010

It will just run with a bit more smoke with too much oil. I have never bothered measuring the oil for the 2 stroke mowers I've had in the past, and the level of smoke was the only gauge as to whether I got it right...

But, also, you can usually see the oiliness of petrol vs mix, but putting some in a glass and letting it sit will (as mentioned) show a layer if there is oil in it after a while.
posted by Brockles at 11:56 AM on May 31, 2010

The two stroke oil I use is colored, usually blue or green and that will tell you if you have mixed it.
posted by TedW at 12:03 PM on May 31, 2010

Dump the old gas in your car. buy new gas/oil for the trimmer.
posted by patnok at 12:05 PM on May 31, 2010

if it is old gas, it might be hard to tell. If it is a small can, just pour it in your car (with a full tank of gas) and redo the trimmer gas.

If it is a five gallon container just re-add the oil, a double helping isn't going to ruin the trimmer, and if it is evident you have too much (excess smoke) eventually just add gas to the mix.
posted by HuronBob at 12:07 PM on May 31, 2010

another thing to consider is once the oil was added to the gas the octane started to go south. after a year you have very little octane left. in other words "bad gas". Now add the issue of ethanol in the gas & you have a recipe for disaster! I don't know about other parts of the country but here in FLA the ethanol is killing us (unless you own a repair shop). Mowers, trimmers. outboard motors, fuel lines all are affected by the ethanol! Not to mention automobile fuel pump failures.
posted by patnok at 12:27 PM on May 31, 2010

Yeah, isn't it usually a color? My two stroke oil is kinda blue-green... and, sure enough, the gas in my two-stroke can has a blue cast to it that the gas in the lawnmower can doesn't.

And @HuronBob: I don't think you want to put even a small amount of two cycle oil in a modern car. That sounds like a good way to mess up some fuel injection. You could probably get away with it if you have an old, carbureted engine.
posted by maniactown at 12:45 PM on May 31, 2010

Yeah, please don't put anything that might have oil in it in your car. No need to turn this from a $300 lesson into a $3,000 lesson.
posted by disillusioned at 12:57 PM on May 31, 2010

don't think you want to put even a small amount of two cycle oil in a modern car.

What do you think petrol is made of? It won't do a damn thing. Cars burn a small amount of their own oil anyway. There is absolutely zero risk in putting a can of two stroke mix into a car.
posted by Brockles at 2:00 PM on May 31, 2010 [1 favorite]

Thanks all.

Confirmed with the Stihl dealer that a double helping of oil wasn't the end of the world, but I'm going to try the glass method to begin with.

If it seems smokey, I'll top the can off with some premium, dude.


posted by BleachBypass at 9:31 AM on June 1, 2010

Glass method seemed to indicate that there was no oil in it already, and since the Stihl guy said even if there was, no biggie....

Threw the oil in and it worked like a champ.


Thanks all.
posted by BleachBypass at 11:12 AM on September 15, 2010

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