1999 BMW 740iL Engine Mount Replacement Cost

There are typically two or more engine mounts in a vehicle. Depending on the vehicle configuration, the engine will either rest on mounts bolted to the vehicle subframe, or will be suspended by mounts bolted to the vehicle's actual frame. In the case of front wheel drive vehicles, these mounts may also support the transmission from the side, and with stabilizers from above. There are several styles of mounts, ranging from solid rubber, to liquid filled. Most modern motor mounts use a liquid filled core, which is contained inside of a composite rubber insert. This allows the mount to flex as needed while still preventing the vehicle from absorbing the vibrations and noise from the engine. This composite rubber insert, also called the insulator, is encased in a metallic housing to provide a firm, stable mounting surface for the engine and transmission, and the portion that connects to the engine is inserted into the insulator and secured via bolts. This design suspends the engine by composite rubber instead of metal.

Vibration in the cabin while the engine is running can be an indication of several component failures, but when the engine is otherwise healthy, the engine mounts are suspected of failure. Not only will they create annoying vibrations and rattles, they can also create a clunk that can be felt and heard whenever the vehicle is put into drive or reverse. If not repaired, the clunking noise will begin to happen at bumps, acceleration, and deceleration, until the mount finally fails, and the engine is able to move freely of that mount. Lastly, when many modern motor mounts fail, there is normally a liquid dripping from the motor mount.

It is normally ok to gently drive a vehicle with bad motor mounts to a repair facility. In situations where very harsh clunks are occurring when the vehicle accelerates, slows, or is put into gear, the vehicle should not be driven, and the motor mount requires immediate replacement.

Engine mounts typically last 60,000-100,000 miles, but can fail prematurely with aggressive driving, outside storage, dry climates, and traffic collisions. Some manufacturers specify an interval to inspect the motor mounts. When the mounts look cracked, are beginning to separate, are leaking fluid, or allow excess movement, they should be changed.

Diagnosing engine mounts is not necessary in all cases, as some vehicles are scheduled for motor mount replacement as part of the factory scheduled maintenance. For most other vehicles, the motor mounts will be evaluated for the amount of travel they allow the engine, if the engine is listing in one direction, whether they have physical damage or leaks, and if they produce vibration or noises in the cabin. If any obvious symptoms are present, the engine mounts will be identified if they are causing the symptoms. Some manufacturers publish specifications for positioning engine and transmission mounts, and failure to adhere to these specifications, or the engine mount gradually shifting out of position, will lead to engine vibrations felt in the cabin, and possible premature engine mount failure. If the technician notices the engine mount appears to be failing, but is installed incorrectly, they may recommend correcting the installation, and testing the existing mount.

Replacing engine mounts requires proper engine supporting equipment. The technician will place the engine support tool across the top of the engine bay, and secure the engine in place. Then, any obstructing components are removed, and the motor mount is removed, given one more final inspection, and replaced if needed. Once the motor mount is replaced, it is checked to confirm proper alignment specifications have been met, and the fasteners will be tightened to specification. All removed components will be reattached, and the vehicle will be tested to ensure the customer complaint has been corrected.

When changing an engine mount at home, never support the engine with a jack or jack stand. The weight of the engine sitting on the pinpoint head of a jack or jack stand can puncture the oil pan, or crack other components. The engine should be supported by an engine brace from the top.

OEM engine mounts are generally more expensive, but aftermarket engine mounts may not meet the specifications of the OEM mounts, and vibration can result. When it comes to engine mounts, you get what you pay for. The original equipment manufacturer mounts are usually the best option, though there are some excellent choices in the aftermarket.

Replacing engine mounts is dangerous, and engines are extremely heavy. There is a risk of being crushed by a falling engine, and crushing a hand between the engine and engine mount pedestal. If safe engine supporting methods are not clearly known, or proper engine bracing tools are not on hand, this repair should not be attempted, and a professional technician with appropriate equipment should complete the job.