I bought this for firearms but after a recent oil change added a cup (8 fl oz) to my car's engine oil like a lot of us older guys did with top of the line oil in the 70's. I would be wary if you have an old car, drive in a hot climate, or have an oil burner as you dilute the oil a bit. However, it will probably make winter starting easier and I would be optimistic that fuel economy would improve by around 5% (mainly in city driving). If you're doing cheap oil changes, a cup of this stuff will double your cost, so you might be encouraged to do the same for fuel economy. In fact I don't think it will extend the life of the car as well maintained engines are extremely rare these days. I also doubt it will solve a real mechanical problem, despite claims to the contrary by other reviewers.
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