Originally Posted by oil_film_movies
Originally Posted by buster
Looks good. This is why I went with regular M1 5w20. I believe this grade has less VII and therefore will maintain its viscosity better when there is fuel dilution. I'd stick with it.
Fuel dilution directly lowers viscosity, and it doesn't matter if it's a higher VII 0w20 or lower 5w20, it will happen.
Looks like this is a case where, at 9k miles, the oil had oxidized in the presence of high fuel dilution as the oil aged in there.
Oxidation raises viscosity, fuel dilution lowers it, so it was creeping back up gradually as oxidation began to take over. Sludge and carbon deposits on rings are the big issues here.
I'd switch to Mobil1 AFE 0w30 (slightly thicker to start with) in this engine this winter in anticipation that fuel dilution will continue to some extent. The slightly thicker 30 weight could seal the rings better.
Since this is a 10 year old vehicle with fuel dilution and questionable ring sealing, I recommend the Valvoline Premium Blue Restore 10w30 treatment this summer.
Good points but I have to disagree. The oil showed no signs of oxidation. Oils with less VII's tend to hold their viscosity better. This was always Redline's best attribute. The starting viscosity of M1 5w20 is 8.9 cSt @100C. The ending viscosity here was 7.54.
M1 0w30 often loses more viscosity than an oil with less spread like the M1 5w20. I would not recommend that oil here. There are numerous UOA's of modern PCMO 0w30 and 5w30 grades become 20 grades when fuel is present. I'd avoid an oil with a large spread unless it's predominately PAO based like EP 0w20.
Oils that show signs of oxidation usually go a grade up or so. Older Amsoil formulations had that issue, such as the early 2000's Series 2000 0w30.
