Originally Posted By: tig1
Changing oil weights is something we did in the 60s and 70s. There is no need to do that now. Use the weight your engine calls for year round.
This is generally good advice - I ended up unintentionally running winter/summer oil. I always ran the same oil year round (M1 0W40, then GC) but starting using 15W40 HDEO several summers ago for an ARX treatment. My car really likes 15W40, and so does my wallet. A couple of summers later I ran dino HDEO again because I knew I was doing a variable valve timing gear job mid-summer and expected to lose a bunch of oil - why should it be $10/L GC instead of $16/gal HDEO?
This summer I elected to run Rotella-T 15W40 because, again, I like the engine character on HDEO (noticeably smoother above 3500rpm than GC, no downside in power or fuel economy) and I'm looking for places to save some $$ and the price couldn't be beat. I bought a 5gal pail to do one change for me and two for my dad who's doing an ARX round this summer for $60 or so. I did my 7L OC for what 2L of GC would have cost me and the HDEO is smoother to boot.
Based on the fact that my vehicle winters in an attached garage, isn't used for commuting, starts and ends in the garage (shopping, errands, dropping off the kids) and likes a 40 a little bit better, I'm on the hunt for T6 as a new year-round oil so long as it's as smooth and quiet as its 15W40 cousin. I'd run 15W40 HDEO year round if I lived in a warmer climate. Perhaps if anything I may alternate between Rotella T6 and 15W40 to save some $$ in the summer.