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DIY: Replacing Engine Mounts

Does your engine bounce around under in the engine compartment? Do you see the cooling fan cutting a hole into the hood? Was that bump you just went over your engine falling out? Maybe you'd better read this before it does.
» Engine Mounts 101
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» Electronic-Hydraulic Mount

Electronic-Hydraulic Engine Mounts
In the spirit of making a mechanics life more interesting, there are electrically controlled engine mounts. Basically it's a hydraulic mount that has two chambers filled with fluid. A large orifice valve and a small orifice valve connect the chambers. The large orifice is a rotary valve while the small orifice is always open. The small orifice makes the mount work like a stiff shock absorber.

When the engine is idling, a vacuum motor turns the large orifice valve to the open position. This allows more fluid to move between the two chambers. This makes the mount softer and absorbs engine idle shake. The Powertrain Control Module (PCM) controls when vacuum is applied to the large orifice valve through a solenoid valve.

Above idle speed, vacuum to the large orifice valve is vented and closes. It goes back to the small orifice operation and becomes stiffer. To check it, apply vacuum to the engine mount with a hand vacuum pump and note the reading. It should remain steady. If it drops the engine mount is bad and needs replacing

On some Lexus vehicles a diaphragm pulsates between the two chambers of the engine mount. This causes a counter vibration to the engine vibration, canceling it out and allowing the engine to idle smoothly. If you have a problem with this type of mount, you'll need to go through a diagnostic routine to check the engine mount and the wiring.

After reading this I'll bet you wish you became a Doctor like your Mother wanted you to be.

» Part 1       » Part 2       » Part 3
Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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