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After figuring out it was the Mobil causing the head gasket leaks I stopped for years then the 0W-40. No Mobil for MoVolvo ever again.
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I'm not understanding how an oil would cause a blown headgasket.
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Dunno, but according to the owners manual 5w40 covers the widest range of temperature, so that's what I'm going with. I'm confused by their thoughts on 5w30 and 10w30. Apparently in Europe they run heavier oils than we do in North America. I would not consider 30 a light oil, but very normal, and currently on the heavier side compared to what many manufacturers are now specifying.
I like 5w-40. I have a bunch of that (Rotella) in the garage still. Using it in all the Volvos.