Well, my FB25 burned a quart of oil between 15k and 20k miles. I added a quart of GC 0w-30 then. That's what I had in the garage. My stash dwindles. I just hit 22,500 miles and changed the engine oil and manual transaxle/rear diff fluids. I sent in samples of the engine oil and MT fluid for analysis. Over 7,500 miles, the oil was: Original fill: 5 qt. PP 0w-20 0.5 qt. GC 0w-30 Makeup oil @ 5k mi: 1 qt. GC 0w-30 Standby for UOA! I refilled with 4 qt. NAPA 0w-20 and 2 qt. Valvoline VR1 Synthetic 20w-50. The VR1 quarts were $1 and I imagine reasonably close to the NAPA/Synpower formula, so I figured, why the heck not? They were in my stash, this car burned a bit of oil, and VR1 is blue. That's all the reason I need. The car calls for 5.5 qt. and 6 brings it right to the full mark. The brew calculates to: cSt@100 11.37 cSt@40 66.58 Yes, it's a heavier blend. But, it's summertime and I want to use the VR1. I'm not so worried about warranty issues, as I have a receipt for a whole case of the NAPA stuff. I will update this thread on any catastrophic loss of MPG, engine failure, or zombie apocalypse caused by my use of other than 0w-20.