Engine mount failure: how to tell, and what to replace with it

An engine mount is a rubber block bonded to a metal bracket, and on many modern cars it is fluid-filled to damp idle vibration. It is a wear item with a finite life, and it is one of the most frequently misdiagnosed parts on a German saloon — because the symptoms it produces look like a dozen other faults.

Symptoms that genuinely point at a mount

• Vibration through the steering wheel or seat at idle, particularly in gear with the brake held, that smooths out above about 1,200 rpm.
• A single thud or clunk when you engage drive or reverse. The engine rotates on its axis and hits the end of its travel.
• A knock over sharp bumps or on full lock — the same movement, triggered by the road instead of the gearbox.
• Visible engine movement. With the bonnet open, have someone brake-torque the car in gear briefly and watch: excessive lift or rock means the mount is no longer holding.
• A collapsed or cracked rubber block. Look for separation between rubber and metal, and for a mount that is sitting visibly lower than its neighbour.

Symptoms that are usually something else

• Vibration that rises with road speed but not engine speed — look at wheels, tyres and drive shafts first.
• Vibration only under acceleration — check the inner drive shaft joints before the mounts.
• A misfire at idle feels remarkably like a failed mount. Read the fault codes and check smooth-running values before ordering anything.

Which mount, and how many

Left and right engine mounts carry the weight and are the ones that wear. The transmission mount takes the reaction torque and usually lasts longer, but it is worth checking while you are underneath, because a failed engine mount transfers load into it and shortens its life.

Replace the two engine mounts together. The reasoning is mechanical rather than commercial: fresh rubber sits higher and is stiffer, so if you fit one, the engine rests at an angle — the new mount carries most of the load, wears quickly, and the exhaust and intake ducting end up under tension they were not designed for.

The step people skip

Rubber bushes must be tightened with the vehicle at ride height, not hanging on a two-post lift and not with the engine unsupported. If you torque a mount while the suspension is at full droop, the bush is permanently preloaded in one direction and will transmit vibration from the moment it is fitted — and it will fail early.

1. 01Support the engine from below with a jack and a load-spreading block. Never work under an engine held only by a jack.
2. 02Bring the suspension to ride height — load the hub with a second jack, or use ramps.
3. 03Fit the mount hand-tight, settle the engine, then torque to the specification in the workshop manual.
4. 04Re-check exhaust alignment and the clearance around the intake ducting before you close the job.

We stock engine mounts for the W205 C-Class and for the W246 / W176 platform. Send us your VIN and we will confirm which side you need before it ships.