[dansgt]

I would not recommend running anything other than the recommended viscosity in an engine except for cases where the engine has very high millage (over 150k). the manufacture recommends a certain viscosity based on the clearances inside of the engine, when it is new the clearances are very tight and the thicker oil will not flow through the tight gaps as well as the thinner oil will. this will cause premature engine wear and lead to early failure to internal engine components.
as for the synthetic switch, the problem with it in a higher millage is it cleans it too well. the regular oil deposits particles in the small clearances of the engine and gaskets, when you run the synthetic, you remove all this and could bring up leaks in the engine where parts of the conventional oil had sealed it. the problem that someone mentioned earlier with the particles getting stuck in the filter is preventable, run the synthetic for a week or so and than change your oil and filter. But overall, dont switch to a full synthetic oil unless the car was broken in on it, go with a synthetic blend. over 75k miles or so i'd recomend just sticking to conventional oil, especially if you have any leaks on the engine, they'll just get worse with synthetic.

[chris1]

Originally Posted by 00SlvrStang Both of the oils you mentioned are NOT synthetics anymore. They are made from regular oil but considered synthetics. If you want a true synthetic go with RP or Amsoil.

unless you have an infinite amount of reserves from when they did sell true synthetic..lol

[Cesar2cool]

Ok so im switch back to 5W20 But how many quarts do i need 2 get?

[Garhfer]

mine takes 6.5

[Cesar2cool]

so buy 7 quarts in other words?