Help! I Poured Oil into the Gas Tank of a Lawnmower

July 3, 2008 | by Fred (email) |

Actually, I didn’t 🙂 But this did just happened to someone close to us who poured used oil (from automobile oil changes) into the gas tank of a Craftsman Push Lawnmower. I guess there should have been labels on the containers…

I thought this might happen to someone else out on the web, so I give some tips below for how to fix it.

Before I start, note the following disclaimer: Accidentally mismatching fluids in an engine could lead to overheating, fire, engine destruction, serious injury, or even death (in rare, worst case situations). These instructions will require you to empty gas out of your lawnmower which, if not done properly, is an environmental hazard and adds to the danger of fire/explosion in this type of fix. If you’ve made the mistake of pouring oil into a gas tank and you choose to try to fix it yourself using our method below, you do so at your own risk. We recommend taking it to a service center 🙂

Steps for Fixing A Lawnmower With Oil in the Gas Tank

Pouring oil into the gas tank of a lawnmower engine isn’t the end of the world. You’ll probably be able to get the lawnmower working just fine by following these steps:

  1. Make sure you’re working in an open, well-ventilated area. This should be done outside.
  2. Disconnect the spark plug wire from the spark plug.
  3. Empty out the regular oil from the lawnmower following the lawnmower’s regular oil change instructions.
  4. Empty out all the oil and gas mixture from the lawnmower’s gas tank into an approved gasoline container. If you have a push mower, this can be complicated because you’ll need to turn the mower over in most cases. For riding lawnmowers, there’s likely a fuel hose you can disconnect.
  5. Refill the engine’s oil resevoir to the appropriate level according to the manufacturers’ instructions.
  6. Refill the engine’s gas tank with new gas.
  7. If applicable, prime the engine using the push button primer.
  8. Start the lawnmower.

You’ll likely end up with white smoke billowing out of the exhaust for the first few second as the engine burns off the oil. In the end, the engine will likely start up find and you’ll be good to go.

If the engine still won’t start, you may need to replace the spark plug, which could be covered in oil [thanks Jennifer], or repeat steps 5-6 one more time. If the engine won’t start after all that, you should take the lawnmower into an approved service center. You may have gummed up the carburetor and it will need to be cleaned in order to start the engine.

What do you think? Did this help you? Do you know anyone who’s done this before?

Image Courtesy of Ansik.

16 Responses
  1. Jennifer says:

    I’ve heard of this… I’d also add to your instructions that if you still can’t get it started after changing the oil, you should change the spark plugs, as they are likely coated in oil.

    We have a push power.. no gas here!

  2. modernemama says:

    No but I did put gas in my diesel tank once. Just once.

  3. Fred says:

    Jennifer-Excellent point. I’ve ammended the post.

  4. robert says:

    my kid put diesel in his gocart gas engine. i drained the tank and replaced the spark plug but it won’t start.

  5. B Naste says:

    Happened to me today… Like an idiot I put the gas in the wrong tank on my push mower. Followed these steps and after a smokey engine for a few minutes it worked. Thanks

  6. Aaron says:

    can anyone help me? i have accidentally left gas and oil in my mower over the winter, and flipped it upside down. it worked the first time i used it, but now it wont again. it seems the entire engine is coated in oil from muffler to spark plug, and i need advise. someone suggested squirting a little bit of ether into the spark plug chamber and pulling the cord, creating a small controlled explosion, but i don’t know if this is a good idea. any tips?

  7. tamara says:

    thank you i sure did not want to buy a new one,and yes i did it and if some one would have put a lable or wrote on the can we would have been just fine. thx agian

  8. Mike Parkhurst says:

    Mark O’Brien on used your article on how to rid oil from a mower’s gas tank. In one of his steps, he says to just unscrew a bolt from the base of the carburator with pliers. It says to pull off the fuel bowl from under the carburetor; spray carb cleaner into the bowl and onto the area above the bowel. Then screw the fuel bowl back on.

    One of our questions is that your instructions are for a push mower but you did mention riding mowers. We have a zero turn radius Kubota and somebody sabotaged our gas tank and poured a gallon of oil into a 6-gallon tank. Our calculation is that there’ s about a gallon of oil in it. The Kubota dealer in our area became angry when we called him about it saying that we were accusing them of being saboteurs since we hadn’t touched the mower since they brought it back from a 50-hour maintenance, even though it’s got only 29 hours on it and said we could not come there ever, ever again.

    So now we’re stuck with no Kubota dealer within hundreds of miles.

    How do we get the gas out of the tank? They (Russell McEwen at Central Kubota in Waxahachie, TX) said that it was impossible to drain a tank on a Kubota; they said the gas tank had to be removed. We complained to the office in Fort Worth, TX, and they agreed with him and said too bad.

    We are following your steps and need to know how to remove the carburetor. And how do we clean the fuel filter, which is filled with amber oil? The technician came out to our house and siphoned off a sample and said, Oh you have bad gas.” And the fuel gauge won’t move at all; the gas tank is full and the meter says it is empty. When the technician was asked about that, he just smiled and would not speak. He just kept smiling and smiling.

    He took a sample back with him and now we are left with an expensive 23-hp Kubota with 29 hours on it and no one will do anything except scream at us.

    Dave Murray in the Service Dept in the regional Kubota office in Ft. Worth, TX, said there is nothing he can do about it. Russell McEwen stated that in January of this year, he decided the customers don’t matter at all. He said he doesn’t care about them. And he got angry because I said that the customer service is the Holy Grail of a business. Is there anything you can do for us with this problem of getting the oil out ourselves, the company and with what these two men have said?

    Kind regards,
    Mike Parkhurst

  9. Lisa says:

    My teen son put oil in the gas tank of the push mower because “he didn’t know the difference”. **shaking my head** I see others have done the same thing. Thanks for the advice. I’ll pass it down to him so he can fix it.

  10. Susan says:

    I just did this – to a brand new mower, yet….My only excuses are my glasses were slipping down my nose, the sun was bright making it hard to see, and – wait for it – the gas and oil are on the opposite sides of my old lawn mower. Thanks so much for this tip. I did not want to have to take everything apart on a brand new lawn mower. I’ll try this. There was no gas in it yet since I was just putting it together. I did dump the oil out by turning the mower upside down. Hope I got enough out.
    Thanks again….

  11. Leigh says:

    I just mistakenly put oil in the gas tank of my mower. I wondered why the hole was so much bigger than I remembered and why the oil was so low after just one mow. I have tipped it and drained the contaminated gas out. Then put a little more gas and swished it around and drained that, but the mower won’t start. It tries but is sluggish. I guess I will have to have my son remove and replace the spark plug. I feel silly but see that the mistake has been made by others. I am new to mowing. Ugh.

  12. alex says:

    Many thanks. This worked for my lawnmower perfectly!
    I followed instructions and exactly the same – after changing gas and after 4-5 changes of spark plugs, and about 10 retries i finally managed to start engine.
    It’s an old German “Takumseh” four-stroke engine. I accidentally poured engine oil into a gas tank. There was a little oil so i taught it wan’t matter, but it did. It didn’t want to start.
    Then I emptied the gas tank (I did not empty oil tank, though), poured new gasoline. I noticed the engine starts but shuts down quickly. So I change the spark plug which was greasy from oil. I changed i think 4-5 spark plugs and finally it started working.
    I think main thing is to empty gas reservoir and change few spark plugs. (you can later clean spark plugs, and they will be good as new…there are few videos about that on YT).

  13. Mary Hill says:

    My son accidentally mowed the lawn last week with the oil mixture inside the gas tank , now today the lawn mower won’t start , he also poured that same oil mixture into the gas tank again omg! definitely a blond moment i’m wondering if we can fix the lawn mower by draining the oil mixture out and removing the spark plug just like you guys are suggestion or is the lawn mower damaged because he did in fact mow the lawn last week with the oil mixture in the gas tank, he is 15 and my husband has given him the job i’m mowing the lawn 🤦🏽‍♀️

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