Ok, I change my oil every 3-5 K with castrol GTX 20-50 and runs like a charm. This time I thought Id splurge and bout fully synthetic mobil one 15-50. After it ran for about 3 minutes, it started clacking and loud lifter noise would come and go. I drove it for a little bit and it improved a little but it still sounds like it has VERY think lubrication in there. It idles alot louder, doesnt seem as tight, and the valve train is alot clackier than normal.

Does anyone know why its doing this? Should I drain it and put my regular oil back in?

I thought this stuff was supposed to be the best.

Regards,

-Andy

car has 126K.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K