850 Turbo Transmisson Noise
 

I just had my transmission flushed out at the local dealer and they also put in a quart of a Castrol additive . It was a Volvo rebuilt trans that was working fine and not making any noise. Since the dealer flushed the trans and put in new fluid the transmission is makes a wining noise when in gear. It shifts fine, but has developed this wining sound.

I'm trying to find out if there is more than one transmission fluid that could of been put in the transmission. What would be the correct transmission fluid for an 850 Volvo automatic?

Number one, check the fluid level just in case they didn't get it full or overfilled it. It needs to be warmed up and idling in park. They also want you to shift thorough each gear for a couple seconds before returning it to park and checking the stick.

There are a number of different transmission fluids. Wrong fluid can cause it to slip badly or grab roughly.

The correct fluid would be Dexron II or III depending on where you pull the specification. Problem is Dex II was superseded by Dex III and in reality Dex III isn't made any more. Dex III was consolidated in with Mercon so you can find "Dexron/Mercon" quite easily at any auto parts store, convenience store or Walmart. On the back it will say what it's approved for and Mercon III is listed.

Where it gets a little complicated is if you want to go synthetic. Some Volvo drivers and Volvo technicians say that the transmissions aren't made to use it and that you shouldn't. Other people say it's fine and they run it without problem.
My 2 cents, it's just a better grade of lubricant and should work better (lower operating temp and better lubrication) since it's still made to a particular specification and again as long as it lists Mercon III or Dex/Mercon on the back it should be the same. I'm running Type F fluid as it's a trick we used to do to GM turbo hydro transmissions to get firmer shifts. Kind of like using B&M's "Trick Shift" but way less expensive.

The additive shouldn't cause any problem. Personally I use the Lucas additive because I've had good luck with their products. It's a transmission fluid "conditioner" I add when I flush, they do make a stop leak but that is a different product.