lately i have been complaining that my fuel consumption increased after the recent service and repairs.
also i feel like there is a slight whine in the engine..

last time i refueled, very soon after the service i used woolies 98 premium. (i generally use 95 prem. )
the day before, i bought just standard unleaded 91 from united servo..
to my surprise, my fuel consumption went back to normal levels and even below (i saw 5.6 on highway reset, and around and under 10 city driving versus 13-14 range before refuel) car also drives a bit smoother now

another thing i noticed is the new engine oil mech used is thinner than my previous one.
i dont know what he put in there, and i have no idea what was there before. but here is my theory

i think, the thin engine oil combined with 98 octane fuel, stressed the engine, increasing friction. and my fuel consumption went up.. also car lost some level of power.

going back to thicker and more lubricant 91 unleaded.. eased up the engine a bit, and now its smoother and burns less fuel.

does that make any sense?

if so, can we say there is a direct relation between the engine oil used and type of fuel used..
so if i use thicker oil, which increases lubrication but slightly reduces performance, i could benefit more from using high octane fuel?

i dunno if i'm rambling or making any sense :kb:

Interesting concept. I would have imagined that thinner oil allowed the parts to move more freely.

They are unrelated, the octane of the fuel simply means it doesn't detonate as fast, or detonates faster leaving a more efficient engine, i'd say its you not being used to the oil or possibly a bad batch of fuel.

I agree, oil is unrelated to this. Quite the opposite, I think. I put 15w60 in the Magna a couple months ago and fuel consumption shot straight up, comparatively. I was previously getting 9.5-10.5l/100km average per tank, with the new oil I was struggling to get under 12l/100km. Safe to say that oil lasted a week before I changed it out for something more suitable (5w40), and fuel consumption has returned to normal.

If you added a fuel additive, I have found it can increase consumption in the tank that it was added (I have experienced this with Caltex Techron 5000). I have noticed about 0.5-1.0l/100km increase (No, I don't subconsciously plant the foot down on that tank because fuel additive=racecar).



so if i use thicker oil, which increases lubrication but slightly reduces performance, i could benefit more from using high octane fuel?


Short answer is no, because 3rd gens don't have knock sensors. You may have a small improvement in fuel economy, but effect in performance will be negligible