Dear malloy1,

Hope you're well. The motor mounts in 900 series cars are not the solid rubber blocks used in the 200 series cars. The 200 series mounts relied on the elasticity of the rubber. Over time, heat and stress cause rubber to lose its elasticity. The 200 series mounts would break: the top and bottom steel mounting plates might separate from the rubber, into which the plates had been embedded.

The 900 series motor mounts have steel mounting plates and a rubber shell, in the center of which is a viscous gel. That gel helps to damp engine vibrations.

The 900 series motor mounts slowly lose elasticity, as the rubber ages. In extreme cases, the mount will rupture, and the gel will leak. You will feel the vibration through the floor pan, because the engine is resting on the steel frame.

You can assess motor mounts' condition by looking at the gap between the oil pan's bottom and the top of the cross-member under the oil pan.

When the motor mounts are fresh, there will be about 1/2" (13mm) of space between the oil pan's bottom and the top of the cross member. You should be able easily to insert your fingers into the gap.

As the mounts age, that gap narrows. By the time the gap is about 3/16" (4 mm), it is time to replace the mounts.

As a result of a road hazard, I had replaced the motor mounts on a '93 940 (September, 2004). Those mounts are still in good order.

Driving on relatively smooth roads prolongs motor mounts' service life. Driving on poorly-maintained roads, or deeply-rutted dirt roads will shorten motor mounts' service life. Turning and braking gently prolongs motor mounts' service life. Abrupt stops and sharp turns - that cause the engine to lurch - put extra strain on motor mounts.

Hope this helps.

Yours faithfully,

Spook