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 a new mount in. Sometimes, it’s a simple operation, but fairly often, there is some complicated disassembly to gain access and allow the engine to be raised sufficiently.
Costs of Engine Mount Replacement
Engine mounts are usually replaced in pairs, though, it depends on the problem exactly. 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.
Using $100 an hour as a labor rate, below are some estimated motor mount replacement cost on common vehicles, assuming they will be replaced as pairs:
- For a 2007 Jeep Wrangler with a longitudinal 3.8-liter engine, the labor time is estimated at around 3.2 hours. A pair of factory engine mounts is about $268, and Anchor mounts cost about $102. The total cost to complete the job would be about $588 using OE parts, or about $422 using aftermarket parts.
- For a 2009 BMW 328i with a 3-liter engine (also longitudinal), the labor time is estimated at around 3.9 hours. A pair of factory engine mounts costs about $260, and a pair of Rein engine mounts costs about $105. The total cost to complete the job would be about $650 using factory parts, or about $495 using aftermarket parts.
- For a 2009 Nissan Altima with a 2.5-liter engine, the labor time to replace the two primary engine mounts is estimated at 1.4 hours. On this design, the transmission-side mount is typically called a transmission mount. A pair of factory mounts costs about $402, and Westar mounts cost about $79. The total cost to complete the job would be about $542 using OE parts, and about $219 using aftermarket parts. On this Altima, there are also front and rear lower mounts that resist engine torque. The labor time to replace these is estimated at 1 hour. A pair of factory lower mounts costs about $209, and Beck/Arnley replacement parts cost about $69. The total cost to complete the job would be about $309 using OE parts, and about $169 using aftermarket parts.
- For a 2009 Toyota RAV4 with a 3.5-liter engine and front-wheel drive, the labor time to replace the primary engine mounts is 2.3 hours. A pair of factory engine mount costs about $367, and Beck/Arnley parts cost about $134. The total cost to complete the job would be about $597 using OE parts, and about $364 using aftermarket parts. There are also front and rear lower engine mounts for this vehicle, as with the Altima. The labor time to replace those is estimated at 2.5 hours. A pair of factory lower mounts costs about $254, and a pair of Beck/Arnley replacement parts costs about $115. The total cost to complete the job would be about $504 using OE parts, and about $365 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 most cases, the engine will then have two mounts that it hangs on, more or less.
One will be at the front engine cover and attach to one side of the vehicle frame. The other will be at the transmission at the rear of the engine and attach to the other frame rail.
The mount on the transmission end is sometimes called 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 happen 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 solved, 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.