I & my friends use to use BP Coarse + in the 1970s, 20w/50. We all noticed over a few months that our engines lost idle pressure. We knew our engines were not going bad all at the same time.....something has happened to the oil. Mate even scuffed a piston in his 454 Chev, which he claimed was the oil.
So I rang the BP hot line & told them the story....
Aaaah, yes they said, we friction modified the oil. You what? Never heard of FM. Because of reqd fuel economy laws in the USA, they were putting FM in the oil to make it thinner at operating temp...to get better mileage.
I now use a performance Aussie oil which is non-FM, 10w/60. There are a couple of brands here that are non-FM & it is stated on the container.
Maybe Lucas has added FM....