Inside your engine and transmission are a lot of things rotating and pounding away; you know stuff like pistons, flywheels, torque convertors, crankshafts, etc. As a result, when running, your engine block, and everything attached to it, has a tendency to vibrate and bounce around a bit. Fortunately, you won’t feel this because all this vibration is absorbed by your engine mounts. The problem is they may not perform their job well forever. After a while (100K-150K miles), the rubber in some motor mounts deteriorates. When this happens, you usually know it because you can start to hear things. For example:
When your car and motor mounts are new, the inside of your passenger cab should be whisper quiet. Acceleration will be smooth and engine noise will be minimal. When your car starts to get up there in years, your previously noiseless interior can start to be infiltrated with buzzing sounds. This sound will be evident whether your car is idling or moving. In most cases, though, it will get louder when the engine RPM increases.
Another symptom of failing motor mounts is a thump or clunk when you hit the gas. This occurs because your engine actually flops around several inches in the engine bay when you accelerate. When you let off the gas, it falls back into place with a thump. This is usually due to motor mounts that are actually broken.
Types of motor mounts
There are all sorts of types of motor mounts today. The original old-style mounts are just a sandwich of two metal mounting plates with a slab of rubber inside. One plate mounts to the engine, one to the body and the rubber in-between dampens the engine vibration. Another type of mount is similar but has a fluid inside which really helps to dampen any vibrations.
Fancy motor mounts
A few automobile manufacturers have gone high-tech with their engine mounts. Audi, for example, has mounts that can change their stiffness based on RPM. The mounts provide a soft cushion at idle, but when you hit the gas, they stiffen. This stiffening allows more feedback and gives the car a tighter feel. Chevrolet has been using Magneto Rheological (MR) shocks for some time and the folks at Bob Fisher Chevrolet of Reading, PA, tell us the MR motor mounts are on the way.
What to do if you suspect your mounts are bad?
If your car has over 100k miles on it, start paying attention to the way the engine feels, especially when you accelerate. Does it vibrate? Do you hear or feel a physical bump or bang when you lift off the throttle? If so, bring it to your local mechanic and have them look at your motormounts. As we mentioned, broken motor mounts can start to damage other engine and drivetrain parts, so don’t delay if you think you have an issue.