better fuel economy cruising at 115km/h then at 100?

[zskinner]

hey so last week i replaced my CTS, MAT and Oxygen sensors and now im getting awesome highway driving fuel economy, but its weird cos when i do a long highway run driving at 100km/h i get about 7.4 - 7.6L per 100km, but when cruising on the same highway at 115km/h i get more closer to 6.8L per 100km/h. can anyone explain this to me ????? my only guess is that the engine seems happier revving a bit higher (at 115km/h it revs about 2100 revs, and 100km/h it revs at about 1800 revs). if someone can maybe confirm they have noticed the same thing do yous reckon maybe some 3.45 diff gears would actually help fuel economy? as it would rev higher at 100km/h? cheers for any replies

[GetToDaChopa]

Makes no sense. There are other factors involved besides just the speed. So just through your anecdotal hearsay you can not come to a final conclusion you would need to test it many times. I recommend you just forget about it and worry about something else.

[zskinner]

well each run was on the same highway, around the same time of the day and the temperature outside wasnt very different each run, and im not worrying about it, more so curious cos i'd rather be getting better fuel economy if i can....... and i dont know what anecdotal means? and im not trying to come to any "final conclusions", more so peoples opinions, thoughts and ideas.......

[DevilDRake]

maybe @ 100 it kicks back some times for slight hills and stuff, 115kph it wouldn't need to

edit: What's CTS, MAT?

OFFTOPIC: Are Oxy Sensors easy to replace?

[zskinner]

ahh true true, makes sense ay . the cts is the coolant temperature sensor (hides behind/underneath the alternator and screws into the front of the intake manifold), the mat sensor is mass air temperature, i think thats what it stands for (screws into the back of the intake manifold), and the oxygen sensor is easy mate, just gotta jack up the left-hand of the car up a bit, unscrew the old one and screw in the new one (though unscrewing the old one may take some work lol i needed a small hammer to help). thats if you have a vn-vp. your info says you got a VY? not too sure about ecotecs mate. p.s. thanks for your input

[sporty custom]

well at 115 it might be in a sweet spot at 100 might be lauboring a tad

[peter p]

I notice the same thing,i was looking at getting a new diff and was thinking of going 3.45 so i drove around in 3rd all week and got better fuel economy, the RPM is about the same for a 3.08 in 3rd as a 3.45 in overdrive. I think it might be that its not as bogged down going up hills,also the 3.8 vp's torque is 292nm@ 3200 RPM so maybe you get better fuel economy as you get closer to its max power.Be good to here form someone with 3.45 gears if they get the same thing,but if i go 3.45 i will be likely to kick it in the guts more and fuel economy will be out the window

[zskinner]

thanks heaps everyone ay cheers for your inputs