Can someone tell me where it is located on 4.2 a6 c5 engine and what would be the easyest way to get to it. Help me out Please

The whole front clip of your car has to come off, then the timing belt must be removed...Prepare yourself for a BIG repair bill. Mine cost $1,600 mostly labor. While you're in there, might as well change the TB, tensioner, water pump and anything else you can think of.

<center><img src="http://pictureposter.audiworld.com/97126/110_1001.jpg"></center><p>I replaced timing belt myself @ 105k with thermostat, tensioner, tensioner rollers, ribbed belt and rear camseals at the same time. All about 12 hours, a lot of work. Much easier to do with the front removed (see pics of my A8). Spent about $400 on parts and fluids.
Pros - you dont have to do it again

The accomplished foreground blow of your car has to appear off, again the timing belt have to be removed...Prepare yourself for a BIG adjustment bill. Mine amount $1,600 mostly labor. While you're in there, ability as able-bodied change the TB, tensioner, baptize pump and annihilation abroad you can anticipate of.

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Thermostat (http://www.prothermostats.com/)

The accomplished foreground blow of your car has to appear off, again the timing belt have to be removed...Prepare yourself for a BIG adjustment bill. Mine amount $1,600 mostly labor. While you're in there, ability as able-bodied change the TB, tensioner, baptize pump and annihilation abroad you can anticipate of.

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Thermostat (http://www.prothermostats.com/)

Agreed. I took one look at the Bentley manual for doing the thermostat on our 4.2 and made an appointment at my local shop.