How Do Motor Mounts Break?

Motor mounts keep the engine in the engine bay of a vehicle. All vehicles use motor mounts, whether the mounts are made of a soft material (rubber or rubber-filled oil mounts) or a hard material (steel). Motor mounts come in two pieces: one piece attaches to the engine, which fits into the bracket that is bolted to the frame of the vehicle. The metal mounts rarely break, and are usually used for racing, because they contribute to a rough riding vehicle.

The most common reason for a broken motor mount is aging and use. The rubber is susceptible to dry rot from the constant temperature changes in the engine compartment. This process normally takes many years. The combination of temperature changes and the stress put on the motor mounts when the driver puts the vehicle in gear or takes off from a stop wears the rubber out. Oil-filled motor mounts break for the same reasons, but also might eventually leak oil through the dry rot. While the mount might not look broken, it cannot do its job if there is no oil inside the mount.

Motor mounts are stressed by driving aggressively on the street or by racing at the track. Each time the vehicle is put into gear or the driver steps on the gas pedal, the torque in the engine moves the engine, stressing the motor mounts. With aggressive driving, the stress put on the mounts is much harsher than if the driver is driving normally. With abuse, the rubber in the mounts might break apart, even if the mounts are not old or suffering dry rot.

Installing a defective motor mount (rare, but it happens) can cause motor mounts to break. A defective motor mount might break immediately or it might break after a few trips with normal driving.