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So apparently at Home Depot in my area, pre-mixed 2 cycle fuel is in a grey bottle and 4 cycle is in a green bottle. And at Lowe's, it's exactly the opposite. The last time I bought fuel, I bought at the other store and picked based solely on color. This means I have now run about 48 ounces of 4 cycle fuel through the engine of my 2 cycle string trimmer. I know, stupid me for not reading the label.

As I was using it today, it would stop running if I let it idle. I thought that was weird but pressed on. Eventually it died while I was using it at full throttle. I have not been able to restart it at any choke position. It's currently cooling down in the garage.

Have I done permanent damage to the engine? What should I do?

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  • Better fit at mechanics.stackexchange.com (we do small engines there as well)? Also, you buy regular fuel at Home Depot? O_o
    – theUg
    Commented Jun 9, 2014 at 2:16
  • @theUg You can buy 40:1, 50:1 and 4 cycle ethanol free fuel in a 32 ounce cans, which lasts longer than regular gas. TruFuel.
    – Tester101
    Commented Jun 9, 2014 at 14:02
  • @longneck just curious, what was the end result? did your 2 cycle engine survive the abuse?
    – n00b
    Commented Apr 21, 2016 at 14:55
  • No, it never started again. Considering how little it cost, it wasn't worth fixing.
    – longneck
    Commented Apr 21, 2016 at 15:01
  • Its been 3 years, what happened?
    – Kris Bird
    Commented Nov 24, 2017 at 22:22

2 Answers 2

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There is quite the extreme possibility there has been permanent damage done. 4 cycle engines do not need oil mixed with the gas to provide lubrication, since it has oil in the crankcase. Two cycle engines have to have oil mixed in the gas to provide the lubrication needed, since there is no oil in the sump. When you used the 4 cycle gas, there was no much needed oil mixed with the gas. There may be a small chance the engine has not seized, it may start again, but the life of the engine has been greatly reduced.

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As Jack said, you almost certainly did permanent damage to the motor. The piston ran without oil for a very long time and running it at full throttle was just about the worst thing you could have done. Even running the motor lean on oil or fuel mix can and will damage a piston/cylinder. Believe me, I have done it with 2-stroke dirt bikes.

When you pull the starting cord do you feel much less resistance than you did before? I'll bet yes, and this is proof of the damage.

You may get lucky and can find a replacement cylinder and piston and repair it without too much cost. Even a catastrophic failure like this usually only affects the cylinder and piston. Although the complete lack of oil may very well have hurt the crank bearing as well.

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  • Fortunately, I didn't run it for very long, and I didn't try too hard to start it after it quit. And it does feel like normal when trying to pull the start cord. Hopefully if I run some 2-cycle fuel through it then it won't be completely dead. I'm not liking my chances, though.
    – longneck
    Commented Jun 10, 2014 at 1:03
  • No, this last comment is pretty hopeful. It's not what I was expecting to hear. Keep us posted.
    – Speedy Petey
    Commented Jun 10, 2014 at 1:47

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