How to Start a Car with a Flooded Engine
FixMyCar explains what it means when an engine is flooded and how to get it started again.
Book a car repair nowEllie Dyer-Brown
Monday April 29 2024
4 min read
If you can’t get your car to start and you notice that it’s cranking very quickly when you turn the key, a flooded engine could be to blame. This is particularly likely on a cold day when the engine requires more fuel to run smoothly while it warms up.
Find out what it means when your engine floods, what causes it to happen and how you can fix it in this guide.
In a nutshell: You can sometimes fix a petrol car with a flooded engine by opening the bonnet and waiting twenty minutes for the excess fuel to evaporate. Failing that, try starting the engine with the accelerator pressed to the floor. Read on for more detailed instructions.
What is a flooded engine?
When someone says an engine is flooded, it means that the combustion chamber has been flooded with too much fuel, stopping it from igniting.
Check out this guide to learn more about how car engines work.
Starting a car with a flooded engine
First, open the bonnet and wait for the excess fuel to evaporate (probably about twenty minutes). After you’ve done that, follow these steps to get your car started:
Crank the engine, keeping the accelerator pedal pushed to the floor.
Continue cranking for up to ten seconds until you hear the engine try to start.
Once it has started, allow it to rev for a second or two, then hold it at a high idle speed for a few seconds.
After ten seconds or so, if the engine still hasn’t started, there’s likely a more serious issue at play. Take your car to a local mechanic who can tell you what’s going wrong and how to fix it.
What causes a car engine to flood?
Petrol engines often flood when switched off too soon after starting during cold weather. When the car is switched off, the unburnt fuel remains in the engine, wetting the spark plugs and making it difficult to start again. This can also result in 'bore wash' when the fuel removes the oil around the cylinder's piston rings.
Vehicles with small, four-cylinder engines are most susceptible to engine flooding, but it can happen to any petrol car.
What are the signs of a flooded engine?
It's relatively easy to tell if your engine has been flooded. Here's what to look out for:
A strong smell of petrol, usually near the exhaust
Black smoke coming from the exhaust
Your engine won't start or starts and quickly dies
Fast cranking or a whirring sound when you turn the key in the ignition
However, if you notice these symptoms and are unable to start your car despite following the advice in this guide, it's important to take the next step. Contacting a mechanic is the best course of action to diagnose and resolve the issue.
Frequently asked questions
Unfortunately, a flooded engine won’t fix itself, but the process of getting it working again is usually simple.
Providing there isn’t a fault causing the engine to flood, you should be able to get it working again in a few simple steps. To do so, you need to balance the air-to-fuel ratio.
The best way to prevent your engine from flooding is to allow your car to warm up properly when starting in the cold before you switch it off again. It should take a few minutes at most; wait until the idle speed drops and the sound of the engine changes.
No, diesel engines can’t be flooded because they are built differently. Learn more in this guide.
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Ellie is FixMyCar's Content Manager. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.