Accidentally put Gas in the Oil Tank of your Lawn Mower?


If you’ve accidentally added gas to your lawn mower’s oil tank, don’t panic, as it has happened to me and other gardeners in the past. I’ve been there too, and I can offer a simple solution to safely remove the gas from the oil tank.

Quick Answer

Quick Steps For Draining The Oil Tank:

  1. Disconnect Spark Plug
  2. Don’t try to start the mower 
  3. Drain oil tank
  4. Change Oil Filter
  5. Refill the oil tank with fresh oil and drain again (to flush excess). Possibly 3 times (It depends on how much gas you put in the tank)
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How to Drain Gas from Lawn Mower?

How to get gas out of the oil tank of your lawn mower

How To Get Gas Out of the Oil Tank in a Lawn Mower

Drain oil tank 30 minutes

Disconnect The Spark Plug

remove lawn mower spark plug

Locate the cover for the spark plug and pull it off, exposing the spark plug. Use a spark plug wrench to loosen and remove. Here’s how to locate the spark plugs on mowers with Briggs & Stratton engines.

Draining the Gas From The Oil Tank

drain gas from lawn mower

The first thing you’ll need to do after the engine has been shut off is to remove the entire contents of the oil tank. This should be as simple as locating the oil drain plug that you would use to drain old oil during an oil change. 

Make sure you drain every single drop of gasoline from the oil tank of the mower.
Even if it appears that any liquid remaining in the oil tank could be oil and not gasoline, you still want to drain all the liquid as has mixed with gasoline anyways, and is not good to to make the mower engine run regardless.

After you’ve completely drained the contents of the oil tank, leave the oil tank lid of the mower open overnight to let any gas remaining in the oil tank dry out before putting new oil into it.

Be sure to do this outside in an open area where dangerous fumes can escape and the interior of the oil tank can dry completely. Follow these steps to drain the oil from your mower.

Change The Oil Filter

Depending on the type of mower you have, the type of oil it takes, and the type of oil filter that your mower uses, you may or may not have to change the oil filter after this happens.

That being said, you can obviously treat this as an opportunity to change your oil since you’ll need to put new oil in the oil tank anyway, so you may as well change the oil filter at the same time and provide the new oil with a new oil filter that has not been contaminated with gasoline.

Filling Oil Tank With Fresh Oil

fill gas lawn mower

Your lawn mower will require new oil, after which you do not want to put any gasoline or mixture of gasoline and oil into the oil tank, even if there is only a small amount of gasoline. This can seriously damage the mower engine and turn out to be quite expensive in the long term.

If leaving the oil tank open and out to dry overnight did not dry up the oil tank well enough, you will need to pour new oil in and drain that also before again adding new oil.

If the oil tank is already sufficiently dry and empty, you will only need to add new oil once. If you still smell gas after adding the oil, you may need to repeat the steps of draining again, letting it dry out, and filling again. Here’s a short guide on the types of oil available for your mower.

See also my guides on:
Using Car Oil in a Lawn Mower
SAE 30 vs 5w 30: Lawnmower Motor Engine Oil Performance Comparison

Start The Engine

start the lawn mower

After getting all of the gasoline out of your oil tank, changing your oil filter, and adding new oil to the oil tank, you can now safely try to start your lawn mower’s engine again. 

As long as you have not been constantly trying to run your mower with gasoline in the oil tank, your mower should be totally fine.

If your mower will not start, you need to speak to a professional mechanic. 

At this point, your problems extend beyond just simply performing an oil change, and trying to fix the inner workings of your mower engine can cause more damage and prove more costly than necessary.

Estimated Cost: 20 USD

Supply:

  • Oil Rags
  • Drain Pans
  • Fresh 2-Cycle Oil

Tools:

  • Screwdriver or Wrench

Materials: Cardboard/Ground Cover

Here is a good walkthrough video showing how to get gas out of the oil tank:

Changing & Draining Your Walk Behind Lawn Mower's Oil

What Not To Do

As soon as you realize that there is gas in the oil tank instead of oil:

  • Immediately shut off the engine.
  • Do not attempt to start the engine until you have completed all the necessary steps to make sure that the lawnmower is safe to be used again.

What Happens if You Put Oil in a Gas Tank?

By continuing to run the engine, you could risk serious damage to your mower, as well as a danger to yourself and others.

Oil serves as a lubricant in most machinery, so by running your lawn mower with gasoline (which is much thinner and a solvent) instead of oil, it is possible that the gasoline won’t allow the engine to be properly lubricated, which could lead to extensive damage to engine parts like the crank bearings, pistons and piston rings, cam bearings, motor, and other parts. 

Any serious damage to the engine of your mower will likely require the aid of a professional to fix, as the extent of the damage might not be evident just by looking at specific parts of the engine. 

Don’t try and mess with your engine if it won’t start and if you aren’t sure you know what you’re doing.

Here is an example what happens when you put oil in a gas tank:

My lawnmower after my boy put gas in the oil tank

In Summary

Handled properly, this can be a minor accident that can be fixed relatively easily.

  • Be sure to shut off the engine if there is any amount of gasoline inside the oil tank.
  • Completely drain the oil tank using the drain plug and allow the oil tank to air out and dry overnight. Do this outdoors.
  • Fill the oil tank with new oil. If needed, drain the oil tank again to ensure all of the gas is out before adding new oil again.
  • Try starting the engine.

If it works your mower is good to go. If not, seek the help of a professional who can take a look at your lawn mower’s engine and properly assess any damage that has been done to avoid making matters any worse.


You may also like…

My Lawn Mower Starts Then Dies: What’s Wrong?

My Lawn Mower is Not Getting Gas to Spark Plug [5 Fixes that Work]

How To Stop A Lawn Mower From Smoking – Easy Fix

How To Fix A Lawnmower That Will Not Start

2 thoughts on “Accidentally put Gas in the Oil Tank of your Lawn Mower?”

  1. Hi Alex, my name is Lily I live in Harvest, Alabama and I made this mistake. I poured gasoline into the oil tank. Of course not having realized what I had done I keep trying to turn the mower on. Eventually a neighbour came over and tried to help me also, then he asked me if it had gas and he pointed to the gas cap. That’s when I realized what I had done.
    I later carefully tilted my mower and poured out the gas and whatever oil was in there. Afterwards, I put the oil cap back on and stored my mower back in the garage because I knew it wasn’t going to work right away. I figured maybe it just needed to dry out and it would be OK. It’s been almost 3 weeks, I poured some new oil in there and I tried running it and white smoke came out everywhere. My neighbours told me that it was just burning oil. So I pushed it along a little bit mowed half of my front yard and it turned off on its own. I am just curious, is there a chance that I could still salvage my mower? As I think that I did not properly drain it or let it sit outside to dry out without the caps … I am just curious what are your thoughts.

    Reply
    • Hi Lily, Thanks for writing in. I apologize for not getting back sooner. I’m actually over in Huntsville so HI! 🙂 As for the oil issue, you would want to fill it and drain the oil a good 3-4 times to make sure you are getting all of the gas out. It is blowing through good oil but that is really the best thing you can do to get all the gas out.

      Reply

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