Oil Viscosity

[Janusz]

I know there are many posts on this topic, but I have relatively easy access to either Rotella 5W40 synthetic or Mobil 1 in various weights. In either case, my records indicate that my car has always had synthetic oil. I'm lloking for a recommendation for summer driving in the Midwest. Thanks.

[GrantG]

15W50

[Zef]

You can check in your owner manual...the viscosity rating vs the outside temp. sheme is there.

[Janusz]

Thanks. 15W50 it is.

[movin]

Rotella 5W-40 is great if you don't already burn oil because of worn valve guides or rings. Last time I checked Mobil1 15W-50 lacked the robust anti-wear qualities that Rotella has. For me Mobil1 always increased oil leakeage, don't know why though.
If you think you need more viscosity because oil consumption try Castrol High Mileage 20W-50, a good choice and actually does have some synthetic content, good anti-wear additives too.
If you must use a synthetic look at Mobil1 20W-50 for motorcylces it's way better that their 15W-50 for cars.

[GrantG]

If you want the whole story, look here:

http://www.lnengineering.com/oil.html

[PSJoyce]

I’ve been using Rotella T Synthetic CI-4+ 5w40 since March, when it replaced whatever the PO was using. RTS’ HTHS viscosity is 4.2, and it has lots of P (1397ppm) and Z (1552ppm) (LN Engineering). Plus, by the indicators I can measure – no oil consumption, no leaks, good oil pressure – it seems to be working well. When the weather was colder, the motor spun much quicker when starting.

That said, with most of the recommendations here favoring higher viscosity oils, I may go to a 15w50 or 20w50 in the summer, and use RTS in the winter.

Paul