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Gaz Robinson
Gaz Robinson, Auto mechanic and MOT Tester
Category: Car
Satisfied Customers: 735
Experience:  18 years knowledge of the MOT test and general automotive skills.
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Daihatsu sirion: There is an overdrive switch in my car. I

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There is an overdrive switch in my car. I am using it when driving downhill because it helps me to let my car move slower. Can i use it for such purpose?

Good morning and thank you very much for your question.

Turning off the overdrive on your automatic transmission car has the same effect as changing up a gear with a manual transmission car when coasting down hill. The lower the gear, the greater the engine braking. This is called engine braking.

With automatic gearboxes, the gears will not always change down by themselves, so you need to either use the gear lever to change down, or turn off the overdrive.

The main reason you'd want to employ engine braking is to descend a steep hill. In such a situation, riding the brakes might overheat them and cause them to fade. It is absolutely fine to turn off the overdrive when coasting down hill, and will not cause any damage to your transmission.

I hope this answers your question, but if you need any further help, please reply to this answer.

Best regards, Gary.

Customer: replied 4 years ago.
If the symbol of overdrive lights in front of me. Does this mean it is off or on ?

Thank you for your reply.

The overdrive in on when the light is illuminated.

Regards, Gary.

Customer: replied 4 years ago.
i got confused. I turn overdrive on during driving downhill to decrease the usage of breaks. Right?

Sorry, you need to turn the overdrive off which will increase the engine speed and increase engine breaking. This will have the same effect as changing from fifth to fourth in a manual car.

I hope this helps.

Regards, Gary.

Customer: replied 4 years ago.
let me explain to you what is my case. When i press on overdrive switch the light turns on and my car starts moving slower as if it moved to a lower gear. Isn't this opposite to what you told me.?

Yes this is the opposite to what I would expect in the UK. Perhaps things are different in your part of the world. Turning the overdrive on when cruising will lower the engine speed.

An increase in engine speed will increase the engine breaking effect. So to slow your car down when driving down hill, you need the engine speed at it's higher speed setting.

Best regards, Gary.

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