If you are bleeding the brakes, you do not need to start the engine. In fact, it is probably preferable not to put it into action at this time. Depending on the weather, you may either do it inside or outside of the house. However, you may do it indoors, rain or shine.
It is necessary for the engine to be running in order for you to push the brake fluid from the vehicle. In any event, you will not need to start the engine in order to complete the task.
Do You Bleed brakes with the engine on or off?
I work as a mechanic, and starting automobiles to bleed brakes is an uncommon occurrence. The lack of vacuum assist makes it a little simpler to push the air out when the engine is turned off, or at the very least makes it easier to feel in the pedal when it is turned off.
Do you have to run the brake fluid pump when bleeding?
While the pump would be required to run if you were attempting to bleed that system (ABS), if you were only attempting to bleed the base brakes, the pump would not be required to operate. When you depress the brake pedal on your car, brake fluid is responsible for the braking action.
Do you have to have the engine running when bleeding calipers?
No. When bleeding the brake calipers, it is not necessary to have the engine running at the time. If the wheels are not stopped and the shifter is slid into gear with the bleeder open, this might result in a perilous situation, which could be fatal.
How do you Bleed brakes with a vacuum boost?
When the engine is operating, it provides a vacuum boost to the braking system. There must be no boost in order for the system to fully drain all of the air out of it. Simply press the brake pedal until a solid pedal is felt, and then bleed each caliper (if fitted) until all air has been expelled from the braking system. With the engine turned off, bleed the brakes (at the calipers).