For years ive added STP to my gassers and theyve gotten extremely high mileage out of them. But has any1 ever added it to their 15w40 diesel pickup?

I would never add STP or other "treatment" to my oil,in any engine. It can messwith the additives already present in the oil. Read this from the latest Blackstone newsletter, which is a reprint of a Road Rider magazine article from 1992: http://www.blackstone-labs.com/newsletter.html

Lucas is good to add in a diesel.

No offense, but this from a guy with three gassers? Have you actually used Lucas in a diesel? Not trying to pick a fight, just wondering if you really are speaking from experience.

No offense taken. I worked with my father and a couple of other guys at a shop down in southern florida and with my father's company "marine hydraulics." Mitch (one hell of a mechanic) has always put lucas in diesels and did so with every oil change he did last summer (a few cummins and a PSD.) Also every time my father does engine work and changes the oil on 150ft+ yachts on these huge volvo and cat diesels. More of an opinion, but I also think a few guys on here do so also...

Fair enough. Their in-store demonstration displays make it look like it turns the oil into some form of jellied adhesive-like substance. I don't know, it just looks like the viscosity is increased to the point of becoming... well, not good.

Admittedly, I myself am not speaking from any experience with it. I've tried an array of fuel additives, but never anything in the oil.

I used to run lucas in my 1959 vw beetle. I checked the oil one day and it was milky white !! wasnt from water either (summer time 100+ f for months) [:@]

so i dumped the oil, filled and flush 3x's to get the lucas out....

VW Type 1 air(oil) cooled engine + Lucas Oil Stabilizer = No Good

Not sure why, but I have had a VW Bug my whole life (the same one, long story) and every mechanic that has worked on it has told me not to use that stuff in the Type 1 motors. I know people with high-mileage waterboxers though that swear by it.