I didn't want to hijack the recent thread about Shell Rotella oil that had started moving away from the Op's topic.  So I thought I would ponder this in a new thread.  

About 3 weeks ago, i switched from modern conventional 10W30 oil to Valvoline VR1 conventional 10W30.  This oil was added at the same time i replaced my clutch and replaced some engine oil seals.  I'm wondering if the higher ZDDP content of this oil and it's added friction reduction properties have contributed to the drastic improvement in gas mileage or the more efficient(new) clutch set is the culprit.  At the time of clutch replacement, i noticed it slipping only once, at which point i removed the trans that evening.  It is possible that it was slipping unnoticed until I noticed it that day.   The stock flywheel was resurfaced at a local machine shop, but not lightened to the best of my knowledge.  But I imagine the resurfacing process inherently takes some weight off.  

The engine is stock except for EGR delete and Cat delete with 208.000 miles on the clock.  I can see no evidence of past rebuilds.  Gas mileage went from approx.  17 MPG to 20 MPG.  Can this oil improve gas mileage like that?  Or is it more likely that the new clutch and slave/master cylinder are responsible?

 

 

2 hours ago, Reptoid Overlords said:

It is possible that it was slipping unnoticed until I noticed it that day

This is more likely the biggest culprit of mpg lose. Can't imagine the oil causing an increase in mpg but, maybe?

That'll help with the higher price for me whether it helps MPG or not, appreciate that.