Can you bump start a diesel?

We’ve all been there – we get into the car, push the clutch in, turn the key in the ignition, and… nothing. Dead battery. So now we have to go through the pain of either calling a breakdown service to get you going, or flagging someone down to try and give you a jump. And that’s if you’ve got any jump leads – if you don’t you might be a bit stuck.

However, there is another way to get your car going if you’re stuck, and that involves either a hill or a group of people willing to push your car, and that’s bump or push starting. Generally it’s accepted that bump starting a petrol is no problem, but there seem to be some reservations and concerns about bump starting a diesel. In this article we’re going to go through whether you can bump start a diesel and how you should do it.

Firstly – what is a bump start?

Bump starting is also called “push starting” and is sometimes called “clutch popping”. Bump starting a car basically means putting the car into gear and either rolling down a hill or having some willing volunteers push your car. 

When you start your car normally, the starter motor engages and turns the engine over. However if your battery is dead, your starter won’t work, as the energy required to run the starter motor comes from the battery. Rolling the car means that instead of the starter motor turning the engine over, the rotation from the wheels actually turns the engine over. Putting the car into gear connects the engine and gearbox, and while you are rolling, slipping the clutch allows the wheels to turn (they’ll be locked if the clutch is up, and you’ll just coast if the clutch is in.)

It goes without saying that you can only do this in a manual car. Don’t try to do this in an automatic – you need a clutch pedal in order to bump start a car.

How to bump start a diesel car

1. If you’re on a hill, make sure you can roll the car without hitting anything. If you need some helpers to push you along, make sure they put you in a position where if you start rolling, you won’t crash into any other vehicles or pedestrians.
2. Switch off any ancillaries or anything else that might put a load on the battery – this includes radio, air conditioning, fans, heater, lights, etc.
3. Put the car into second gear. You do this because second gear will engage at a low enough speed, but also you won’t need as much torque to get the engine going in second as you would in first. If second doesn’t work you can also try third gear.
4. Take the handbrake off and pull the clutch up to the biting point.
5. Have your volunteers push the car. With any luck, once you reach 10-15mph your engine should start.

Why is bump starting a diesel different?

Well, to be honest, it isn’t. A diesel manual will react in the same way as a petrol manual if you try to bump start it. I drive a diesel – and I’ve had to bump start it once or twice without issue. 

However – there are some things you need to consider. 

A diesel engine uses heat and high compression to ignite the fuel. Diesel is a lot less flammable than petrol, and in petrol engines, spark is used to ignite the fuel. Modern diesel engines use glowplugs to preheat the cylinders to ensure they are hot enough to ignite when the key is turned in the ignition.

What you may find is that if your battery is completely discharged, it may not provide enough power to heat the glowplugs. If this is the case, and it’s a cold day outside, you may find bump starting a diesel is almost impossible. In this case you’ll need to charge the battery somehow. If after charging the battery there isn’t enough power to engage the starter motor but you can operate internal functions such as the heaters or the radio, you may have enough juice that the glowplugs can heat the cylinders and you can try again.

Additionally, most modern diesel engines use direct fuel injection. Opening and closing the fuel injectors requires electrical power, and if the battery is completely dead, it won’t have the power to open and close the injectors. If this is the case you may find your attempt at bump starting fails. 

Finally, your car will also have a fuel pump which provides fuel to the injectors. The fuel pump is usually electrically powered, and again if your battery is so flat that it can’t provide power to the fuel pump, bump starting is pointless and won’t work, as the engine won’t be getting any fuel. Usually you can hear the fuel pump priming when you turn the key in the ignition – if you can’t, you may want to jump start instead.

Are there any safety concerns with bump starting a diesel car?

Generally no more so than if you bump started a petrol. One thing you MUST be aware of is that with the engine not running, the vacuum system used for braking will not work. You may be able to push the brakes once or twice, but after this your pedal will likely go rock hard and require immense pressure to push it down. 

Obviously this is a safety concern if you’re bump starting on a hill, as you may not be able to stop the car if you can’t get the engine going. My advice here would be to allow the car to get up to maximum 20mph and if it doesn’t look like you’re getting the engine running, stop the car and try again. Don’t allow the car to freewheel down a hill – this is extremely dangerous.

Can you bump start a diesel van?

Of course you can – there’s nothing different between diesel engines in a van and in a car. However, if you’ve got something large like a Mercedes Sprinter or VW Crafter, these are very heavy vehicles and won’t be easily pushed by a group of volunteers unless you have a lot of them. A hill will still work fine. Just ensure you consider the above point regarding safety, as a van is bigger and heavier and will pick up speed down a hill quicker.

Can you bump start a diesel automatic?

You cannot bump start any automatic vehicle – whether it’s a diesel, petrol, LPG or anything else. If it’s an auto, bump starting is not possible. You will need to either get someone to give you a jump, or you’ll need to charge up your battery and try and start the engine that way.

Can you bump start a diesel in reverse?

I wouldn’t. The reason for this is two-fold – obviously if you’re in reverse you have less visibility and control over where the car is going. Not only that but reversing down a hill trying to start your engine just seems like a needlessly dangerous thing to do. Additionally, the point we made earlier regarding torque at the wheels – reverse and first require the highest amount of rotational force, so it will be significantly more difficult to try and bump start in reverse anyway. 

Of course, you may find a situation where you need to bump start in reverse unavoidable, such as if you’ve parked in a bay and you need to reverse out or something – in this case, get someone to push your car so that you can bump start going forward, or jump your car. Reverse bump starting is not a good idea.

Can I push my own car and then get in?

You can, but this again just seems needlessly dangerous. I wouldn’t do this, and I wouldn’t recommend you do either.

Can you bump start a diesel with a dead battery?

Based on what we spoke about before, if the battery is completely dead you have issues with no power going to the glowplugs, fuel injectors and fuel pump. If this is the case, you won’t be able to bump start your diesel. However if there’s only a little bit of charge in the battery you should be fine.

Conclusion

Hopefully this helps you out next time you’re stuck and you can’t get your car going. For more automotive advice, stay tuned for our next article!

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