How to Diagnose a Bad Motor Mount

Written by jay motes
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How to Diagnose a Bad Motor Mount
Motor mounts support engines and protect them from damage. (New car petrol engines image by Christopher Dodge from

Motor mounts support an automobile's engine and transmission. A bad motor mount will not properly restrict and cushion the engine or transmission, which can result in damage. An engine or transmission that is moving too far or too quickly due to a bad motor mount may strike objects inside the engine compartment or the side of the engine compartment itself. A thumping sound from the engine compartment during rapid acceleration or deceleration is the usual indication of a bad motor mount. If you hear this sound, you should inspect and repair the motor mounts before serious damage occurs.

Skill level:

Things you need

  • Flashlight or work light
  • Pry bar
  • Wheel chocks

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  1. 1

    Park the vehicle on a flat surface. Place the wheel chocks in front of and behind the rear wheels of the vehicle to restrict movement forward and backward. Raise the hood.

  2. 2

    Use the flashlight or work light to locate the motor mounts. Mounts may be located on the top and bottom of the engine and transmission. The exact number and location of mounts will vary depending on the model of the vehicle.

  3. 3

    Visually inspect each mount for problems. Mounts that are cracked, show areas of wear or have corrosion require replacement.

  4. 4

    Stand off to the side of the vehicle while observing the engine and any visible upper motor mounts. Have a helper start the engine. Instruct the helper to depress and firmly hold the brake pedal while placing the vehicle into drive. Observe the engine and upper mounts. The engine should move smoothly, without a sudden jolt. Movements that are rapid or in excess of one-half an inch indicate a motor mount problem.

  5. 5

    Have the helper shift the vehicle into reverse and again observe for movements. Have the helper slowly shift between drive and reverse a few times. Note if the engine moves more on one side, the front or the back. The engine will move more on the side attached to the bad mount because the bad mount allows freer movement. Have the helper put the vehicle in park and turn off the engine.

  6. 6

    Use the pry bar to apply force to each motor mount. Flex the mount both toward and away from the engine. Mounts should give slightly, but should not move rapidly or freely.

  7. 7

    Use the pry bar to apply force between the motor mount's mounting plate and the mounting surface of the vehicle. Movement will indicate loose or damaged mounting bolts.

Tips and warnings

  • Keep hands, tools and other objects away from the engine while it is running.
  • Stay to the side of the running vehicle in case it moves forward or backward.
  • Carefully flex the motor mounts with the pry bar to avoid damaging other engine components.

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