The best product is auto-rx available from auto-rx.com . It is a lenghty but effective process. There is plenty of discussion of it in bobisthioilguy.com where people are crazy and incredible knowledgable about oil.

By the way 5W-30 is not too thin for your brick. THe weight of the oil is 30 at opeating temperature. 5W is the cold temperature of the oil (winter). It will flow much better at startup protecting the engine better (startup is when most wear occurs).

The original volvo manual recommends 5W-30 in the winter. There used to be a trade off. Better cold temp starting but the additives used to increase the viscosity spread would cause it to burn off sooner (something like that). That was back in the 1980s when the american petroleum institute oil standard was SF. Today oils are much better made. They have the SM standard (last letter increments as the stasndard improves).

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Paul NW Indiana '89 744 Turbo 145K/ '90 745 turbo 127K