Replacing spark plugs on '93 850

A: How frequently should spark plugs be changed? What would be the best choice? There has been a lot of contradictory info about using Bosch Platinum in 850 so I am thinking I should go with the ones provided by a Volvo dealer or can I use bosch 4+. B: Also, is there a way to properly set the torque without using a torque wrench. I saw some pics on Bosch site but was wandering if there is anything Volvo 850 specific or can I just follow Bosch's spec. Thanks for any recommendations.

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B: Bosch recommends 10mm With Gasket 12mm With Gasket 14mm With Gasket 14mm Tapered Seat 18mm With Gasket 18mm Tapered Seat Torque FT.-LBS. 8-11 12-15 19-22 12-15 20-23 14-17 If a torque wrench is not available, hand tighten the plug until it is seated in the cylinder head. Spark plugs with gaskets should be tightened an additional 90°. Spark plugs with tapered seats should be tightened an additional 15°.

On the 20valvers, especially if you tend to do alot of stop start driving, and regular restarts with a cold or semi warmed up engine, I would recommend the +4's or the 4 prong ones from Volvo.

The 20v's tend to run very rich from cold start and are prone to flooding. The 4 prong ones were specified by Volvo when the problem became apparent for the 20v NA units; originally only the Turbo's used them. They are more tolerant to fuel wetting and you've more of a chance you can get the engine to restart if it does become flooded. (without removing the plugs to dry them)

Volvo's interval for plugs is 40k, but you will notice mpg dropping off after 30k, so I renew mine at that interval.

Don't worry about torqueing them- do them up finger tight til the washer contacts the head, then another 90 degrees. I know this doesnt "feel" very tight, but its fine. On a pre used plug, tighten til contact then 45degrees. Only on a cold engine mind. don't attempt to move them with it hot- you run risk of damaging the alloy head. I put a smear of copperslip on the threads- dont like them dry in an alloy head.

Hope this helps.

Tim..