Engine mounts are the rubber-and-metal or hydraulic elements the powertrain hangs from inside the body. Their job is to hold the engine in place and absorb its movements when pulling away, braking and changing gear. When the rubber ages and tears, the engine gains freedom of movement: vibration at idle, a dull thump when starting off, a jolt when shifting. Mounts can be checked without a lift, if the engine is loaded correctly.
The load test, step by step
You need a helper and level ground. The idea is simple: the engine is loaded through the transmission while the car is held on the brakes, and you watch how far it moves.
- Switch off, open the bonnet, apply the handbrake, chock the wheels.
- Start the engine and warm it to operating temperature.
- The helper sits in the driver’s seat, presses the brake fully and holds it.
- On an automatic: select Drive and add a little throttle for 2–3 seconds, then neutral, then Reverse with the same short throttle. On a manual: select first and raise the clutch to the point where the engine starts to pull without stalling; then repeat in reverse.
- You stand to the side by a wing and watch the top of the engine.
What to look for: the amount and character of the movement. Healthy mounts give a smooth tilt of 5–15 mm with a soft return. Worn ones give a sharp jerk with an impact, metal-on-metal knocking and rocking after you lift off. The direction of the movement tells you the side: Drive loads one mount, Reverse the opposite one.
What to look at without load
Half the information comes from an ordinary inspection.
| Sign | What it means |
|---|---|
| Cracks and tears in the mount rubber | Mechanical wear, replacement |
| Oily fluid weeping | A hydraulic mount has failed |
| The engine sitting low, a belt pulled tight | The lower or rear mount has collapsed |
| Traces of metal touching the body | The engine is reaching its travel limit |
| Vibration at idle, smooth on the move | The typical picture of worn mounts |
Hydraulic mounts can look intact from outside and still not work: the fluid has leaked out and an empty rubber pad remains. They are tested under load rather than by inspection.
Not confusing them with other knocks
A thump when pulling away comes from more than a mount. Similar sounds arrive from play in the driveshafts, broken control arm bushes, the gearbox mount, and a propshaft joint on rear-wheel-drive cars.
The regime separates them. Mount knock is tied to load changes: pulling away, shifting, lifting off sharply. Driveshaft knock appears in a corner under power and sounds like rapid crunching. Suspension knock follows the road surface rather than the drive, and the shaking side of the story is on the symptom page vibration at idle.
Another common substitution is a hum the owner attributes to the engine while the source rotates with the wheels. Separating the two is covered in working out where a hum comes from.
How the repair is decided
The labour varies enormously with access: the top right mount on many cars is a half-hour job, while the lower rear one means supporting the powertrain and removing the undertray. That is why an estimate is worth asking for by specific mount rather than “for the mounts” in general.
Two things belong in that conversation. Hydraulic mounts are usually replaced with hydraulic ones rather than cheaper solid rubber: fitting the wrong type brings vibration into the cabin that no adjustment removes. And on cars where the mount is only reachable after removing something else — an undertray, a battery tray — ask what else is coming off, because the answer explains both the price and the time.
A broken mount will not strand you, but it gradually destroys its neighbours: an engine that moves too far loads hoses, wiring and driveshafts. A sensible window is to deal with it within a month or two of the thump appearing.
If you are unsure whether the impact is really metallic or simply a harsh take-off, record the moment of pulling away in the Pro-Stuk app. The app matches the recording with your answers about the regime and shows the likely causes with percentages.
