Yep... I've used it.
I had an older Jeep Cherokee with the 4.0L straight six that blew a head gasket (I think). It had lost compression in one cylinder, and the oil would get milky over 1500 miles.
When I was trading it off, the dealerships wouldn't ever give me anything for it, because it ran rough (compression) and even with fresh oil, it didn't look good. So, I used three cans of 8-cyl (16 oz. size) cans of Restore, along with 4 1/2 qts. of Valvoline's SAE 50 weight VR-Racing oil. PRESTO! No more milky oil!
After about two times of changing the oil at 500 miles, I traded it in, and no problems. The compression was better, good enough that it ran smooth(er), and the oil never got milky. Now, for what happened to it, in the end... Who knows??? That Jeep had become such a money pit, I was willing to do anything to get rid of it, but I'm sure I didn't do it any favors.
From what I understand, oil additives bump the viscosity of the oil up so high, that the valve-train suffers. But, I'm no mechanical engineer, so...
Best of luck!
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Nic
1987 GT 5-spd
Just got back from Sluppy123's. New engine/clutch work fantastically!!!