Just wondered if any body is using the Silkolene pro S 5/40. Ive just bought some ready for an oil change and dont know weather i should have plumped for the 10/40 instead? Car is a 1996 sti V3 RA in standard form.

 

Havent tried that, but i used 5/30 in mine the first time i changed the oil, i did specifically go for very thin stuff to clean the engine out, it had 15/50 in it and had blocked the cam followers. The only thing i noticed was that it used it quite quickly, because it was so thin. I use 10/40 now and its fine.