What Are Engine Mounts For?

It's something that exists in every single vehicle you can buy - but what is an engine mount?

What do a Toyota Corolla from the 1970s, a Ford Ranger from 2015, a Tesla Model S, and a Porsche 991 GT3 RS have in common? They all have engine mounts - or motor mounts more specifically if you're being pedantic - and they all serve the same purpose even if they come in different shapes, sizes, and complexity.

The engine mount sits between your powertrain and the chassis - that's when an engine mount is in its simplest form. They're what hold your engines, motors, and gearboxes in place within the car that you drive, but on top of that they are also designed and engineered to help isolate vibrations and harshness from the passenger cell.

That's right - you don't solid mount a powertrain to a chassis unless it's pretty specifically designed to be a racecar. A solid mount is incredibly uncomfortable, just as how you feel bone-rattling vibrations when you accelerate a go-kart to its top speed. In its simpler form, an engine mount will usually contain rubber bushings that take up the vibrations before they reach the rest of the shell.

On the more complex end of things, soft engine mounts can also protect the engine and other components from unnecessary stresses and harmonics. The little vibrations that can be transmitted from the chassis back to the powertrain can cause small stress fractures and rattle sockets loose.

Very well engineered engine mounts can make engines such as the three-cylinder in the Proton X50 feel completely smooth to the occupants, despite obviously vibrating and rattling when you take a look in the engine bay. This is pretty normal for three-cylinder engines; the Ford Fiesta Ecoboost also goes to similar lengths to improve refinement. 

Higher-end European performance cars even have something known as magnetorheological engine mounts, which simply means that they can change how stiff or soft they are with some clever computer control. It's the same base technology that's found in adaptive dampers, and there are a couple of reasons for this.

The first is that soft engine mounts are needed to help isolate those vibrations and provide a comfortable driving experience, but they aren't great when you're really driving hard and the engine starts to move under load. If you've ever watched an engine on a rolling road or dyno, you will notice that the engine tilts one way as the driver accelerates and springs backwards when they lift off the gas.

Not only does this mean that the weight balance of the car starts to shift as you get on and off the gas, you may also find that the shift lever (for manual cars) starts to move around in peculiar ways. Allowing the engine mounts to stiffen up when necessary adds a layer of precision and control without compromising that comfort when you need it.

But ultimately, engine mounts are engine mounts. They do wear out over time like many consumable items on your car, and if you find that a car is particularly rough when you're driving it - whether it just seems to vibrate a lot or it rocks when you accelerate and deccelerate - it may be worth checking your mounts to make sure they're in good condition.