Fuel consumption using different engine oil

[aaronx88]

Dear all,

For those who have tried different engine oil, has anyone noticed if their fuel consumption either has gone up or gone down due to different weighting of the oil e.g 10w-30 FEO , 10w-40 etc

I noticed an increase in fuel consumption from 6-6.5l/100km to 6.8-7.5l/100km when I changed the engine oil from FEO (mineral) to Motul 4100 (semi-synthetic) 10w-40 on my Jazz. The car travels the same road everyday from home to office and driving pattern remains the same. It also uses the same petrol BP Ultimate throughout.

I'm considering Castrol Edge 5w-30 or the Motul 8100 5w-40 for the next oil change at 30k service for both my Euro and Jazz.

Thanks.

Aaron

[timofytit]

The rating of the oil will definately affect your fuel consumtion. Those figures ie, 10w - 30w etc are the viscosity ratings of the oil at diferent temps. Ie 10w cold and 30w hot. If the viscosity is lower at hot for example 30w instead of 40w, the oil wont be as fluent causing more work for the engine. Also on another note, oil can actually help the movement of the parts inside the engine by surging etc at the right time. I hope this helps you out. PS, in theory, your consumption on the castrol edge will be thicker (lower viscosity) when cold. I would try and match the factory recommended figures of 10-30 with other brands if you like switching oils. Hondas are designed for honda oil.

[aaronng]

Moving to the technical forum.

In the user manual, the Euro can use oils ranging from 0w-20 to 15w-40. The first number shows the viscosity at -18C and the 2nd at 100C. Now, the first number is not as important as the 2nd one because were rarely experience -18C weather. So at an ambient temperature of 15-20C, oils of 0w, 5w and 10w have smaller differences. I have also used semi-synth 15w in a car specified for 10w and at cold start, the engine was running smoother than mineral 10w (GTX3). The difference though is flowability. How quick the oil pump is able to circulate the oil throughout the engine is also affected by the oil viscosity. While 0w/5w/10w oils are able to protect sufficiently when cold, the speed at which they flow throughout the engine is slightly different. In my opinion, the difference is small enough that I would use any one of the 3 viscosities for my Euro.

The 2nd number at 100C is right smack in your engine oil operating temperature. So the differences in viscosity will be more apparent here. As you found, 40 being thicker than 30 affected your fuel consumption. The upside is that since 40 is slightly more viscous, the thin layer of oil on the metal surface is more durable. On street driving, it doesn't make a difference but when you are at the track, a slightly thicker oil may give you worse consumption and slightly less power but that protective film is more durable and should protect better against wear in extended high RPM conditions. In the US, car manufacturers are pushing for 0w-20 oils in their cars because it allows then to quote ridiculous fuel consumption numbers to enhance sales.

I would tell you not to worry between 0w/5w/30w-30/40 oils and instead choose a good oil. Castrol Edge 5w-30 is good, but from my experiences (I used both before), I prefer Edge 0w-40 because 5w-30 is a hydrocracked oil while 0w-40 is a PAO oil (read this (http://ozhonda.com/forum/showthread.php?p=739022#post739022) oil thread on the differences of the types of oils). Motul 8100 (full synth) is also a good oil, and since it is as the same price range as the Edge 0w-40, might be a better choice since it has Motul's extensive research on engine oils backing it.

[dsp26]

i remember a celica forum last night talking about royal purple giving a 9hp gain... wtf?!?!

was dyno tested and gave 2hp gain.

but anyway yes it does affect fuel consumption.. but i think moreso depending on the "right foot".

5/10w30 obviously thinner has less resistance than 10w40. for MY CAR... response difference is VERY noticeable.

anyways what i said is pretty vague as i don't want to get into technicalities so please don't flame me for it.. i know its vague but it answers the question... enough.