As an engine runs and transfers power to the wheels, it vibrates and twists forcefully. Every engine has an arrangement of strong mounts to hold it in place in the frame and to absorb vibration.
Most of the time, the mounts are made of rubber held in a steel cage. Some use oil-filled or hydraulic mounts for better vibration dampening.
Replacing an engine mount is usually a matter of unbolting the mount, then raising the engine off the frame enough to slide the old mount out and the new mount in. Sometimes it’s a simple operation, but fairly often it requires some complicated disassembly to gain access and allow the engine to be raised sufficiently.
The Cost of Engine Mount Replacement
Engine mounts are usually replaced in pairs, though it depends on the exact problem. If an engine mount is replaced because it has hardened up with age, the other mounts are probably in the same condition. If an engine mount is replaced because it has failed mechanically, that in itself can cause more stress on the other mounts.
Assuming £70/hour for workshops and £100/hour for factory dealerships as a labour rate, below are some estimated motor mount replacement costs for common vehicles, assuming they will be replaced as pairs:
- For a 2007 Jeep Wrangler with a longitudinal 3.8-liter engine, the labour time is estimated at around 3.2 hours. A pair of factory engine mounts is about £235, and non-OE mounts cost about £88. The total cost to complete the job would be about £460 using OE parts or about £310 using aftermarket parts.
- For a 2009 BMW 328i with a 3-liter engine (also longitudinal), the labour time is estimated at around 3.9 hours. A pair of factory engine mounts costs about £225, and a pair of aftermarket engine mounts costs about £90. The total cost to complete the job would be about £500 using factory parts or about £365 using aftermarket parts.
- For a 2009 Nissan Altima with a 2.5-liter engine, the labour time to replace the two primary engine mounts is estimated at 1.4 hours. In this design, the transmission-side mount is typically called a transmission mount. A pair of factory mounts costs about £350, and non-factory mounts cost about £70. The total cost to complete the job would be about £450 using OE parts and about £168 using aftermarket parts. On the Altima, there are also front and rear lower mounts that resist engine torque. The labour time to replace these is estimated at 1 hour. A pair of factory lower mounts costs about £180, and non-OE replacement parts cost about £60. The total cost to complete the job would be about £250 using OE parts and about £130 using aftermarket parts.
- For a 2009 Toyota RAV4 with a 3.5-liter engine and front-wheel drive, the labour time to replace the primary engine mounts is 2.3 hours. A pair of factory engine mounts costs about £318, and non-manufacturer parts cost about £115. The total cost to complete the job would be about £480 using OE parts and about £275 using aftermarket parts. There are also front and rear lower engine mounts for this vehicle, as with the Altima. The labour time to replace those is estimated at 2.5 hours. A pair of factory lower mounts cost about £220, and a pair of non-OE replacement parts cost about £100. The total cost to complete the job would be about £395 using OE parts and about £275 using aftermarket parts.
Different Kinds of Engine Mount Arrangements
On an old-style longitudinal engine where the front of the engine faces the front of the vehicle, the engine typically rests in a cradle and has two mounts, one on each side. These both support the weight of the engine and resist the twisting forces as the engine transfers power through the transmission to the wheels. This is most common on rear-wheel or four-wheel-drive vehicles.
Another arrangement is on a front-wheel-drive vehicle where the engine sits transversely, with the front of the engine facing the left or right side of the vehicle. In such cases, the engine will have two mounts that it hangs on to, more or less.
One will be at the front engine cover and attached to one side of the vehicle frame. The other will be at the transmission at the rear of the engine and attached to the other frame rail.
The mount on the transmission end is sometimes called the transmission or rear mount. These mounts do a good job of suspending the engine and absorbing vibration, but do little to resist twisting forces.
A third mount is used for that, which is sometimes called a “dogbone” mount due to its common shape, or a torque strut or something similar. This is usually mounted on the bottom of the engine between the engine block and the frame.
Sometimes there are two lower mounts that resist twisting forces. One at the front and one at the rear.
Symptoms of Failed Engine Mounts
Engine mounts usually use heavy and resilient rubber construction to absorb engine vibrations. One of the things that happens to rubber as it ages is that it hardens up and loses resilience.
Visually and mechanically, an engine mount can still seem fine. However, an old engine mount will often transmit excessive amounts of engine vibration into the chassis.
Sometimes, this can seem like an engine that is running very rough. This is especially noticeable at idle, and it isn’t always easy to diagnose.
One method is to use a small jack to raise the engine and take the weight off the mounts. If it runs smoothly and the vibration is gone, it’s probably bad engine mounts.
A hydraulic engine mount often fails (and causes vibration problems) by leaking out its oil. If a hydraulic engine mount has an apparent leak, it should be replaced.
Engine mounts can fail mechanically as well. The rubber can split and break down, or separate from its bonding material.
On a longitudinally-mounted engine that would allow the engine to rotate too much, it can twist or clunk in its mounts when power is applied. With the hood open, an “engine brake” test checks for this.
Usually, if the rubber has failed, there is still a metal cage that limits motion. However, clunking, vibration, and general harshness are the symptoms.
A dogbone mount on a transverse engine can fail the same way. If the rubber has separated or degraded, there will be too much twisting motion in the engine on acceleration, usually accompanied by a clunk.
One thing that can cause the degradation of engine mounts is oil leaks. Oil can damage the rubber. If there is an oil leak that has saturated a failed engine mount, the oil leak should be repaired along with the mount.