Engine mounts perform the key functions of holding the engine in place and isolating vibration – so they need to be robust and high performance.
There are several different types of engine mounts available. Here’s a quick guide to hydraulic engine mounts, and how they differ from other types of mounts.
How hydraulic engine mounts work
Hydraulic engine mounts are made of rubber, and they feature a hollow centre filled with hydraulic fluid, usually a glycol/water mixture. As well as supporting the engine, the mounts must absorb two main types of vibration:
- Low frequency vibration that comes from shock excitation – accelerating or braking hard and driving on rough surfaces for example.
- High frequency vibration that comes from unbalanced engine forces, such as from firing pulses or any mass imbalance in the rotating or reciprocal engine parts.
To be most effective, a mount must be frequency dependent. This means stiff and highly damped in the low frequency range and the opposite in the high range – soft and light – to prevent the engine from moving due to shock excitation.
This is where hydraulic engine mounts come into their own – they can be highly tuned for optimum dampening of vibration, without allowing engine movement.
So what’s the downside? It comes down to a matter of preference – and budget. While hydraulic engine mounts are very effective, they are more expensive and not as durable as solid rubber mounts, for example.
How they differ to other types of mounts
Other types of engine mounts include metal mounts (metal on metal), rubber mounts (generally solid rubber with metal backing plates) and active mounts, which you usually see on top-range, new-model vehicles.
Rubber mounts are robust enough to hold the engine in place, and they do a great job of absorbing vibration, so they tend to be the standard choice for cars, trucks and utes.
Active mounts are generally vacuum-controlled and respond to changes in RPM.
Signs your engine mounts might need replacing
No matter the type, engine mounts can wear out. While they might last the lifetime of your vehicle, it’s important to be aware of signs they need replacing. Signs of wear include cracks, corrosion or warping. It’s also a good idea to check your mounts if you notice a lurching motion when you accelerate or jolting as you drive along.