Barry. I have seen the Oil issue go both Ways.

Where I worked We had several CAT Diesel Generators. If you used 30 or 40 wt Oil in the one it would burn more Oil then if you used 15-40 wt.

The other 2 you could use single or multiviscosity Oils and they seemed to use about the same amount of Oil.

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84 300D, 82 Volvo 244Gl Diesel