My son added some when he changed to Lucas 5W-20 synthetic (group lll?) oil in his 2002 Ford Focus 2.0L Dohc Zetec. Lucas Synthetic Oil Stabilizer is crystal clear, and is much thicker than oil. Lucas says to use 20% mix, but he only added 1 oz per quart of oil. Car runs fine (replaced Torco 5w-20)might be a tad quieter?
My son like to try different oils, but is not interested in doing any lab testing of what he uses.
He did receive a gallon of Lucas Synthetic Oil Stabilizer, as well as a couple of cases of Lucas 5W-20 synthetic oil. If anyone is interested in testing the stuff, I can mail you some.