OOOHOOH, I know,I know pick me!!!
I went thru the same debate. Did my own test on my 25RS and my buds Boxer ALFA Romeo. And found out for myself.
We tried Mobil and Valvoline (our favorite synthetics) 5w40 and 5w30. The test was done in mid winter of a very cold year avrage temp was 12 degrees F. Ran both oils with our favorite filter, Purelator (still a good filter in my opinion). Over a 3 week period we tested for cold starts to pick our best starting oil. It was mobile 5w30 worked good in both our cars. But the Valvoline 5w40 ran smoother at temp. So he ran VAL 5w40 in his car I used Mobile 5w30. In 5 winter months we ran both oils in our boxer engines in Frekin cold weather. Each did an average of 7200 miles. Results:
~At 500 miles oils ran better than when first fresh.
[email protected] 3500 miles oils started to brown.( My subie was pretty new but mine was darker.) Continued test. (NOTE: It was to freekinn' cold, didn't want to do any work on our cars yet.)
[email protected] 4200-4600 miles noticed a decrease in preformance. ( take offs, revvin, Hard to start, that could have been the cold) Oil was black in my car and Dark brown in the Alfa.
[email protected] 7000-7600 miles got sick of hard starts and bad revin. Drained oil changed filters. Temp was 30 degrees F. Oil was very black in both cars. Thick as molasses also got thick crust film around filters from cooked oil. "eyawza!!!"
Both of us put 5w30 normal cheapy oil in to help clean engines for 2000 miles.
Then switched to Amsoil 5w30, and I use sdf-36 (bigger) or sdf-34 (smaller) filters.
We never looked back
P.S. I became a dealer for the cost breaks not for profit!
The stuff works. Note if you have turbo use 10w30 or 10w40 (if you have an older car). The stuff is really lite and has the best protection. At 6000 miles the stuff starts to turn brown not black. I change my oil 2-3 times a year every 6,000 to 7,000 miles. It works great for both the Subaru's and the Alfa's Boxer engines.
Good luck
:biggest: