The engine motor mounts on most vehicles are designed to isolate the engine's normal movements and vibrations from the vehicle frame and body so the operator of the vehicle will not feel them. In some vehicles the motor mounts are made from solid rubber and others may be hollow rubber with a liquid filling. The solid rubber ones are used in most vehicle engines, while the liquid filled ones are used in vehicles that need additional isolation between the engine and body.
The motor mounts are subject to wear and tear depending on age and how the vehicle is driven. A vehicle with a manual transmission may break motor mounts more often depending on the abuse from the shifting of the transmission. The age of the mounts will vary depending on location. Just like old tires start to dry rot and crack, so do the motor mounts' rubber. A solid motor mount may tear partly and still work fine, but a liquid filled motor mount will leak out the liquid and the motor mount will no longer dampen vibrations from the motor.
In general, motor mounts do not have a scheduled replacement but should last between 5 to 10 years before dry rot or breaking from age-related failure. Motor mounts can get broken from slamming the vehicle, gears over-revving, and letting out clutch or power braking the engine before takeoff. Motor mounts can break in vehicle accidents too. If the motor mounts break due to harsh transmission shifting, the transmission mounts may also get damaged. I have seen mounts break in a year or less due to outside failures. Engine oil or other fluid leaks may get on the mounts, deteriorate the rubber, and cause it premature failure.
If you start your engine and notice that it is making more of a noise than usual, and can feel more vibrations than usual, this is a key sign of a worn engine mount and it may need replacing. If an engine mount is damaged, its anti-vibration properties weaken. An increase in vibrations leads to the engine making more of a sound than usual – something that can be extremely damaging to an engine if it continues for a long time.
Upon starting a machine, you may notice an excessive lurch that doesn't feel or sound healthy. This is a common indicator of a worn or damaged engine mount. This lurch then often steadies into a constant vibration, but you may then also experience a lurch when turning the ignition off.
Often, an engine mount that needs replacing can cause a jolt when changing gears on an attached transmission. This jolt or thump can also be noticeable when travelling at faster speeds due to the engine working harder. If your machine doesn't feel as smooth as usual, this can often be down to a damaged engine mount.
A worn engine mount can often lead to ‘clunks' and ‘bangs' within its surroundings/engine bay. This is as a result of the engine moving around more than normal and making contact with other components, which in turn can cause impact sounds that become quite noticeable.
With use, the metal part of an engine mount does change in appearance. However, if you can see any significant corrosion, cracks or warps to the part, it is likely that excessive wear will be occurring to the rest of the mount. If you notice any cracks or flaking to the rubber aspect of an engine mount, this can potentially limit its performance depending on the severity of the cracks and the route cause. The efficiency and effectiveness of engine mounts relies on their form and shape, and so any changes to this can be damaging to the engine. If you do notice any of these signals, you should look into replacing engine mounts as quickly as possible.