[TwistedCopper]

This is probably going to spur debate, but many say it will cause oil leaks because of the gaskets breaking down if you put synthetic oil in a high mileage motor that has always been run on organic (regular) oil. I'm not sure of the hows and whys but I tried it in my 92 YJ, and it was only a synthetic blend. I figured the people claiming it causes leaks were just exaggerating. After the first 3K mi oil change I noticed 2 small leaks, one at the head gasket and the other the valve cover. I switched back to organic oil and I kid you not the head gasket stopped leaking. The valve cover still leaked but not as badly.

That said, I am seriously considering converting everything in my '05 LJ to synthetic. The mileage is still low on it. There's no way I would even consider it on my 91 YJ with well over 180K miles.