Okay, Let help you out here.

Oil additives are a bunch of hype and are expressly not recommended by the vehicle manufacturers. They are a secondary market for which people get played on thinking they are a necessary need and a fix, but they are neither.

Get yourself the best quality synthetics in the market and you will have none of these issues. Amsoil is the Market Leader in this technology and can outfit your vehicle from top to bottom with the best stuff. Period!

refer to my site: www.weareoil.com
Should you requre additional information let me know and I will be glad to assist in any way that I can.

http://www.weareoil.com/questions_and_answers.htm

Take a look at the above link. This should help you out. I can also give you a complete printout on your vehicle as well. Should you require further assistance email me at rpiescik@comcast.net

I own a 95 volvo 850 with 283K miles on it and still going strong.

Like KlausC says, it's a treatment.

I have used AutoRx on a 740 Turbo, an 850 Turbo, and an 850 20V. It's been nothing but good. It cleaned up all these cars' engines tremendously. The 740 and NA 850 engines benefitted especially well. The cars feel a lot more powerful and engines smoother after the cleaning cycle.

I have also used AutoRx to clean the auto gearboxes and powersteering on all these cars to good effect as well. The sticky/late shift problem on the 740 Turbo was heaps better after two treatment cycles and flushes.

Apart from using AutoRx, I have also cleaned these engines via the Seafoam process (not using it in the engine oil but through the vacuum intake). The 740 had 190K and the NA 850 had 200K kms on them respectively.

Using a good semi-syn or full syn oil in these engines after the cleaning process helps the engines remain clean for a lot longer, and they run a lot smoother and have better fuel economy with non-dino oils in my experience.

The other oil thing you'd want to do with 850s is an annual transmission drain/flush. Too many people don't flush the auto trans until its too late.

AutoRx is a treatment, not an additive. The directions on the bottle says to add and run the engine for a 100 miles or so and then flush the oil and replace the filter. AutoRx is used to remove sludge build up. Not as something you would want to keep adding to the oil at every oil change.
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My name is Klaus and I am a Volvoholic.

Have you been running synthetic? It does a remarkable amount of cleaning on its own. The mechanic might not recommend it because he might see you a little less often.
Volvo consistently recommends not using any additives at all, that said, folks do do flushes.
I'd vote for the Seafoam quick change then synthetic.
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'97 855na, Mobil 1, K&N, various IPD's and eBay's

Here is my 3 cents on additives.... If you have sluge in the engine then an additive might be called for. but an additive in itself is not recomended by Volvo. So there you go.

Not claiming anything beyond my personal experience..

AutoRx did wonders in my engine.

My 850 T5 would start to smoke slightly out the tailpipe if it sat idle for about 5-10 min's..to the point that it failed one emissions test because of visible smoke.
One AutoRx treatment..and NOTHING else..it stopped..
That was 40k miles ago it now has 243k miles..and no more smoke