Coolant flush has almost nothing to do with your engine shaking. Look at the color of your coolant. If it is orange-ish, you are good for up to 100K miles, if it green-ish, then you should flush.
In a nut shell, coolant flush is basically removing MOST of your coolant/antifreeze from the radiator, the engine block, the heater core and the lines, and replacing it with new fluid.
I am more concern with your shaking problem. Can you give a little more descriptive explanation to the problem. Include time of day, idle or driving, intermittent or all the time, etc. The more description you provide, the easier the diagnosis will be.
Tuesday, December 9th, 2008 AT 11:11 PM