When I had 5w-30 in my rex, it warmed up a little quicker than when I switched to 10w-30. Does 10w-30 slow down the engine warming-up process?

 

Probably a fluke. If the oil is what did it, that would mean that 10w-30 is better at preventing friction (i.e. heat).

 

Lighter weight oil heats up faster, which is why we people in the colder regions of the world use thinner oil during the winter. I normally go with a Mobil1 10w-50 during the summer, but use the 10w-30 for the winter. The 50 weight makes my engine feel too sluggish in the winter, and it takes forever to heat up the car.

 

yes 5w-30 heats up faster as it has a lower viscosity (thinner). shouldn't notice much difference in bay area weather. only in really cold regions

 

ok thanks for the responses. i was in the bay area when i changed the oil. even then, you can notice a slight change

 

One of the benefits I have noticed (and correct me if this is impossible) is, during the hotter months, I get a small kick in performance using 50wt. I would think this is from better compression due to the thicker oil allowing less blow-by in the cylinder, especially after running hard for a long time, where a thinner oil would break down. This has only been a theory of mine from when I started using 50wt. Dunno if its correct though.

Can I get a witness?!

 

Even in the summer, I don't think I'd want to run straight 50w, especially with so many different brands making 20w50 now in synthetic. 50wt is going to cause more friction wear at startup.

 

Well, its Mobil1 10w50, abbreviated to just 50. My bad . Its pretty good stuff in the summer, but molasses in the winter. I decided to run the 10w30 after I went out to start the car on the first cold morning of the year and the engine was actually bogging at idle until it ran a few minutes and heated up. Ever since the switch, no problems, even at -6C.

 

synthetic 10-50 is much better than 10-30 because you hae the same range as with the 10-30 and than some

 

If you're not flogging your car on a racetrack for 20,30,40 minutes at a time with high coolant temps, then no, 10w50 isn't really better. It just reduces your fuel economy a tiny bit. Subaru recommends 5w30 or 10w30 for a reason. If you're not using the car drastically differently than what's outlined by the owner's manual as "heavy duty use" then you don't need it.