Driver Knowledge Tests

How to deal with a flooded engine

Why won’t your car start? It turns over, so there’s no problem with the battery, but it won’t fire. Chances are, if you’ve just started it, moved it a few metres and shut it off again, you’ve flooded the engine – this is really common as we sometimes want to move a car under the car port, into some shade or into a better parking spot, but without driving it any more than a few metres.

Flooding the engine has nothing to do with water, but the amount of fuel that’s been introduced into the engine. It rarely happens with modern, fuel-injected cars if the temperatures are normal. If it’s cold or very hot it can happen, too.

Don’t keep letting it turn over because you’ll wear out the battery and you’re making the flooding worse (so much so, that you might have so much petrol in the cylinders that it seeps into the oil). Also, don’t pump the accelerator as this can make the flooding worse.

A flooded engine has too much petrol and not enough oxygen. This wets the ends of the spark plugs and they won’t ignite the fuel.

Preventing flooding from happening

If you have to move your car just a few metres, let it idle for a couple of minutes before you shut it off. This will give the engine enough time to restore the air/fuel balance.

Getting your car started after you’ve flooded it

If you don’t know what these are, you should call a mechanic

There are three options:

  1. Leave it sitting a while for the fuel to evaporate. If the spark plugs aren’t too badly fouled, this can work.
  2. Try starting the engine with your foot flat to the floor. Most car computer systems interpret this as meaning that the engine is flooded. It could take 10 seconds to fire and then it will splutter for a while until the air and fuel are in balance. This is why you don’t want to run your battery down. This sometimes doesn’t work in modern cars. The reason it does work is that it lets extra air into the cylinders
  3. If those options don’t work, you’ll need to either take the spark plugs out and replace or clean them, or get a mechanic to do it for you. Mobile mechanics can help, otherwise you’ll need to tow your car. To get the spark plugs out you’ll need a socket set. To clean them you’ll need some spark plug cleaner from an automotive store.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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