Engine flooded with fuel

What's a flooded engine and how do you fix it?

The car engine flooding is a common cause of breakdowns, especially on cool or colder days when the engine needs more fuel to run smoothly until it's warmed up.

If you can't start your car, this could be the problem. Read on to find out what causes a flooded engine and how to fix it.

Woman looking at overheated engine with steam coming out

What does flooding the engine mean?

A petrol engine floods with fuel when it’s switched off too soon after being started from cold. After switching off, the unburned fuel remains in the engine. That wets the spark plugs, which prevents ignition and makes the car difficult to re-start.

The petrol can also cause ‘bore wash’ when it removes the oil around the cylinder’s piston rings. It lowers the compression, which is why the engine sounds different and turns over more quickly.

What causes a flooded car engine?

A flooded engine often happens when a car’s moved out of a garage onto the drive or moved a short distance to let someone else out. It’s most common in the spring and autumn.

Some engines are more susceptible than others. It’s most likely with small, four-cylinder engines but can happen to any petrol engine in the right conditions.

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How can I tell if my engine's flooded?

You can tell if your engine's flooded when you spot these signs:

  • Very fast cranking (the engine sounds different when you turn the key – usually a 'whirring' sound)
  • A strong smell of petrol, especially around the exhaust
  • The car doesn’t start, or starts briefly and cuts out again

How can I fix a flooded engine?

Before you start trying to clear a flooded engine, it's a good idea to close any doors and windows to your house. That's because the exhaust is likely to be very smokey for a few seconds when the engine starts. If the car's in a garage, make sure the garage door's open and there's plenty of ventilation.

To clear the excess fuel:

  1. Crank the engine with the accelerator pedal pushed to the floor
  2. Continue cranking the engine (for up to 10 seconds) until you hear the engine trying to start
  3. Once the engine’s started, allow it to rev up for a second or two, then hold it at a higher than normal idle speed for a few more seconds
  4. If the engine doesn’t start within 10 seconds there may be other issues and you should switch off and call us for assistance. If you're already a member, you can call us out for breakdown cover
  5. Once the engine’s warmed up, you can switch off safely or use the car normally

How can I avoid flooding the engine?

It’s best to always allow your petrol engine to warm up once it’s been started from cold. This only takes a few minutes – it’s warm enough once the engine note changes and the idle speed drops slightly. You’ll also see the temperature gauge move off the minimum.

Can you flood a diesel engine?

In short, no. Diesel engines work differently to petrol engines. They're not usually at risk of being flooded with fuel.

What if the engine is flooded with water?

If your engine is flooded with water rather than fuel, that’s a different problem. It could cause a lot of damage depending on how much water got in. To avoid flooding your engine with water, it’s best to drive carefully through fords and floods.

Published: 9 May 2019 | Updated: 22 July 2020 | Author: The AA

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