Why Are Motor Mounts So Expensive to Replace?

Key Points

• Most cars have two to four motor mounts.
• A bad motor mount will cause vibration or knocking from the engine.
• You can test for a bad motor mount visually or by rocking it by hand.
• Replacing motor mounts often requires lifting the engine.

While the majority of motor mounts aren’t very expensive in and of themselves, the labor involved in replacing them can be. Most vehicles have two to four motor mounts, which can also be referred to as engine mounts. Their job is to hold the engine in place while absorbing engine vibrations.

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Some motor mounts are a simple combination of steel brackets separated by a rubber block, which is what quells the vibrations. Others are more sophisticated (and thus more expensive) oil-filled hydraulic mounts or even mounts that can vary their damping.

In most cases, replacing at least two of the mounts requires jacking up or dropping the engine, either of which can be a tricky procedure that often requires specialized equipment. That’s a good reason why most folks have it done at a shop. Furthermore, accessing the mounts in crowded modern engine compartments can require removing other parts to get at them, which adds further to the labor cost. In addition, shifting the engine can cause other components to fail that may need to be replaced; examples include stretched radiator hoses and damaged  exhaust systems.

Some modern cars have mounts that hold the weight of the engine while another mount simply keeps the engine from rocking side to side. The latter are sometimes called “dog-bone” mounts for their shape, which also resembles dumbbells. Since these normally don’t hold the weight of the engine and are typically near the top of the engine (though sometimes at the bottom), they’re usually fairly simple to replace for a handy do-it-yourselfer.

What Are the Signs of a Bad Motor Mount?

• Takeaway: A bad motor mount will usually result in vibration and knocking from the engine compartment. 

Since one of the motor mount’s primary jobs is to reduce engine vibrations, a failed mount will allow more vibration to be felt, often accompanied by a knocking noise due to the engine moving far enough to contact other components. This will be most noticeable when stabbing the throttle from idle or when moving the shift lever from Park to Drive or Reverse, as these are instances when the engine moves more than when just cruising down the road.

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How Do You Check for a Bad Motor Mount?

• Takeaway: Motor mounts are likely bad if you can see the engine shift when you press the throttle or if you can move it by hand. 

One way to test for bad motor mounts doesn’t require any tools. While it’s easier to do with a helper, you can do it yourself if you have the proper sightline.

Open the hood, and start the engine. Get in the driver’s seat, and check if you can see the top of the engine through the bottom gap of the hood. If not, you’ll need a helper. (Note: If you use a helper, make sure they’re not standing in front of the car when the following tests are performed, as the car might lurch forward if the brakes aren’t firmly applied.)

If you can see the engine, firmly depress the brake pedal with your left foot, then shift the transmission from Park to either Reverse or Drive. You may notice the engine shift — either fore and aft with a transverse (sideways) engine or right or left with a longitudinal engine. Then, making sure you continue to hold the brake firmly so the car doesn’t move, press down on the throttle with your right foot. This will cause the engine to shift. In either case, if it shifts an inch or more — or if you hear a clunking sound — that indicates one or more motor mounts are defective.

With the engine off, you can also try just rocking it by hand. Also, if you can see any of the mounts, check if the rubber block (if it has one) looks like it’s breaking apart. Hydraulic mounts may leak fluid, while variable-damping mounts may have a loose or deteriorated vacuum hose or a loose electrical wire going to them. 

While you can drive a car with a bad motor mount, it’s not a good idea to do it for long. One bad motor mount can put stress on the other mounts, which will then have to be replaced, as well. A bad mount can also lead to damage caused by the engine shifting.

If you’re tempted to try and replace any of the mounts yourself, an internet search for, “How do you replace the motor mounts on a [year/make/model/engine]?” should give you an idea of what’s involved. It can also reveal how much labor is involved and what equipment is required, both of which are factors in why having a motor mount replaced at a shop can be so expensive. 

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