Very occasionally on a cold start the whole car will seemingly "rock" ... however the starter cranks strong usually on the first "turn over." It feels as if the engine turning is moving the body. In other words the car can mildly rock as of someone shook it. No ugly sounds accompany this shake fortunately. However no matter when I hit the throttle there is no movement of the engine bay for a classical bad motor mount symptom. The starter is a Bosch 100% new which seems be a very stout unit.

Is this rocking caused by a bad motor mount? The only automotive historical experience I have with this were bad motor mounts on my parents car. However the symptom was you could here the engine "clicking" during braking movement.

You don't mention which car ..folks need to make sure you give specifics about their car when asking questions .

I think it could be a fluid mount failing or something similar..you may not be able to see the results of a failing mount until it completely fails... just small hints like you are noticing now .

I take it that this is a manual trans? You should still be able to use the parking brake and let the clutch out to the point where you can see if the engine rocks excessively under load.

Put the car in forward and reverse with the parking brake on hard.
With the hood open, either let out the clutch or give it the gas with an auto tranny.
You'll see a lot of movement with broken mounts.
But you have to test both ways.

I agree- I had a cheap-o fluid mount start to fail, and while it was leaking, the engine ran smooth as glass. And was probably rocking around a lot too. When it finally failed, the engine started making contact with things it normally didn't, and made a lot of noise and vibration.

A buddy of mine had a huge old Chrysler many years ago where the engine would lift up and whack the air cleaner against underside of the hood due to a bad motor mount.

Joel

Some cars have a lot more engine slop than others. If you were just going by visual indications, then you would have to compare yours to an identical model that you knew had good mounts.

Or, if you were familiar with how much your engine moved around normally, and it is now moving around a lot more, and its obvious to you, then that does sound like a bad mount.

Otherwise you may have to have someone look at it (either dealer or ind. mechanic) that has experience with your car.

Is it a new development? What car? My mother's Sunfire with the 2.4L Quad4 has always done that. All the mounts seem to be in good condition.

I seem to remember that our "family truckster" Pontiac 6000 Wagon with the 2.5l 4-tech engine jumped around a lot too.

I believe that the "slop" in a mount (as designed) depends on the inherent vibration of the engine and the desired "smoothness" the engineer wants in the car. Lots of slop means that the car feels smoother- vibrations are absorbed by allowing the engine to rotate, rather than by transmitting them to the body. Even things like gear shifts- if the "jerk" of a gear shift is absorbed by the engine, it will feel smoother to the driver.

When you put an automatic in gear, there is a twisting force. Either then engine will "leap" or the body of the car will leap.