So I have a big vibration in my engine when the 2nd fan turns on it with vibe for awhile then stop, it also does this when the A/C is on, any ideas what this could be? Thanks

 

When the A/C turns on, the ECU Turns on the 2nd auxiliary cooling fan. (The smaller electric one.) Leave the engine running, put the A/C on, open your hood, and watch it. Could be that smaller E-fan hitting it's own shroud, or contacting something else. Just a quick visual inspection would be my first move.

 

you probably have an unbalanced electric fan, if you go through mud and it doesn't spin the mud off of it right away it will create a severe vibration once the mud is dried on.

also check to make sure it's still complete

 

With the vehicle off, try turning the electric fan. If the fan motor bearings are shot, you should be able to feel it as you turn the fan.

 

Has anybody figured this out? I have the same vibration when:

1. E-fan turns on with temp increase.
2. E-fan turns on when I set heat selector to "defrost"
3. When e-fan turns on when I put on the A/C.

It is connected to the e-fan and coincident with the above conditions.. I unplugged the A/C compressor , but still get the vibration when I turn on the A/C. My stock fan started do this just before it fell apart and ruined my radiator. I installed a new e-fan and I still have the vibration under the above conditions. It's not mud and should not be bearings, unless the bearings in a brand new e-fan are shot. Not likely.