Motor Mounts Are Too Often The Forgotten Fix, Gary Goms, Counterman, January 1999. An often overlooked engine component that may need to be replaced while doing engine work are the motor mounts. Any DIYer who's pulling an engine may well find he needs motor mounts.

These rubber mounts can deteriorate, collapse and/or separate with age.

Fluid filled "hydraulic" type mounts can often leak, allowing annoying engine vibrations to be transmitted to the chassis.

Most mounts are designed so that separation won't allow the engine to fall out onto the roadway.

But a bad mount may cause a myriad of problems - many easily misdiagnosed.

Often, bad motor mounts allow the engine to rock and move around, causing noise and interference problems with the throttle, transmission and clutch linkages.

A thumping noise when the transmission is put into gear or when the vehicle is accelerating is a classic symptom of a bad mount.

Excessive engine rocking can also create exhaust leaks where the head pipe joins the exhaust manifold as well as exhaust rattles.

The donut that seals the exhaust joint can be crushed or broken by the motions of the engine, or the head pipe or pipe flange may crack.

Cracked or broken motor mounts can be an annoying source of vibration and noise, typically a clunk or shudder when accelerating hard.

A broken or separated mount may even allow an engine-driven fan to scrape the fan shroud or contact the radiator.

Motor mounts also maintain engine and driveline alignment in front-wheel-drive cars and minivans with transverse-mounted engines. So it's important that the mounts be in good condition.

REPLACEMENT MOUNTS. So, you may ask, when do motor mounts need to be replaced?

Well, the answer is rather straightforward! When they're loose, broken or collapsed.

The mounts support the engine and transmission or transaxle, and help dampen noise and vibration to isolate the powertrain from the rest of the vehicle.

The upper mounts on front-wheel-drive applications also help control engine rock as the engine applies torque through the driveshafts.

When a motor mount fails, one of several things can happen.

If the rubber separates or delaminates from the steel, the mount can break.

While the design of the mount may prevent the engine from literally falling out of the car but it won't keep the engine from twisting or hopping on its mounts every time the vehicle accelerates or is under load.

This can produce thumping and rattling noises as well as overstress components such as radiator and heater hoses, wiring connectors and the exhaust system.

Drive belts or pulleys may also be forced to rub against other components if clearances are tight.

A broken or loose motor mount in a front-wheel-drive application can be even more serious because it may allow engine movements that interfere with the throttle or shift linkage.

Excessive fore and aft rocking of a transverse-mounted engine can also lead to exhaust leaks where the head pipe joins the manifold or cause the head pipe itself to fail.

If the bad mount is an end mount, it may also contribute to a torque steer condition and cause accelerated wear or separation of the inner CV joints on one or both driveshafts.

THE ART OF LISTENING. The noise produced by a separated or broken motor mount often sounds like a bad U-joint or inner CV joint (a clunk when accelerating or placing the transmission or transaxle in gear). So before either of these other components is replaced, the mounts should be checked.

Some mounts are "hydroelastic" and have hollow chambers filled with hydraulic fluid to dampen vibrations that would otherwise be transmitted across the mount to the chassis.

Replacement mounts should be the same (fluid-filled hydroelastic or solid rubber) as the original.

One bit of critical advice: substituting a less expensive solid mount for a fluid-filled mount can increase the transmission of engine noise and vibration to the rest of the chassis.

These mounts may save your customer a few bucks, but won't do the same job as the original.

They feel harsher and transmit more noise and vibration to the rest of the vehicle, and may cause a customer to return with complaints of a harsh rides or vibration.