Fuel Consumption on 3.0

[GTbee]

With my car, it seems the main factor is the length of trips rather than the speed. I've done long trips where I've being doing over a fair bit over 110 km/h where appropriate (sadly hard to do these days) and my consumption was far better than in the suburbs.

[MrPotatoHead]

I got bored driving for 3 hours in northern victoria and worked out that for about every 10km/h over 100km/h the fuel usage increases by 1l/100km.

so for 100km/h ~ 8.2l/100km
for 110km/h ~ 9.2l/100km
for 120km/h ~ 10.2l/100km
for 130km/h ~ 11.2l/100km

I didn't cruise at more than 130km/h for long enough to really watch the fuel consumption readout, but physics says fuel consumption should increase exponentially with speed, so this is fairly rough.

[otb]

Used to own an MY04 Wagon, Spec B, as my reps car.

Did 290,000 km in 4 years, seriously never missed a beat.
Burnt oil at new but it settled down just as the dealer said it would.

A lot of Highway km's obviously for that but if I got under 620 out of a tank something was wrong, and it always had work tools, etc in the back.

Even around town (Melbourne) I would never get below 480 - 500.
Always ran 98 Octane fuel - from new, always got it serviced regularly and (cause it was all on tax I guess) never skipped on what the service required.

Definitely noticed a difference though if you cruise above 3000 rpm for any length of time.

Cheers

[Farugah]

Got back from my roadtrip to Perth, 9000kms and averaged 9.4L/100km which im quite happy with, some of the drivers were speeding (once i told them that i was destroying fuel economy it stopped them ). Thats with quite spirited driving around town.

[hamish_023]

I got bored driving for 3 hours in northern victoria and worked out that for about every 10km/h over 100km/h the fuel usage increases by 1l/100km.

so for 100km/h ~ 8.2l/100km
for 110km/h ~ 9.2l/100km
for 120km/h ~ 10.2l/100km
for 130km/h ~ 11.2l/100km

I didn't cruise at more than 130km/h for long enough to really watch the fuel consumption readout, but physics says fuel consumption should increase exponentially with speed, so this is fairly rough.

Would be interesting to find out what the optimum speed/consumption would be from 50km/hr 60/70/80/90 for each car

[wally09]

Got back from my roadtrip to Perth, 9000kms and averaged 9.4L/100km which im quite happy with, some of the drivers were speeding (once i told them that i was destroying fuel economy it stopped them ). Thats with quite spirited driving around town.

I did the same thing. Same average. Although my average speed was about 140kph. That's as fast as you can use cruise control. This was across the nullabor so straight and flat. You guys with the little annoying efficiency thing on your dash will know that sometimes higher revs in a lower gear is more efficient than straining in a higher gear.

This obviously isn't the case because I was in 6th doing these speeds. But I also was using minimal throttle. So I was getting an average of about 9.5.

[Robbks]

You guys with the little annoying efficiency thing on your dash will know that sometimes higher revs in a lower gear is more efficient than straining in a higher gear. This obviously isn't the case because I was in 6th doing these speeds. But I also was using minimal throttle. So I was getting an average of about 9.5.

have a read of this
http://autospeed.com/cms/A_112611/article.html

although it only relates to the actual engine as opposed to the whole vehicle
interesting reading anyway

[GTbee]

My average consumption is hovering around 15.00L/100. I'm still mostly doing shortish trips but even so I am a but worried. I do rev it out from time to time, always use 98 and swap between Caltex and Shell. Car is a 2005 manual.

My car is on 47XXX, so still 3xxx until the 50,000 service. I'm wondering if there is anything from west_minist's list I can do myself in the meantime.....?

[*]Poor Fuel quality

I always use 98 and alternate between Caltex and Shell

[*]Spark Plugs not Gap to Manual specs

I think I'll leave that for the service. Subaru plugs are hard to access anyway...

[*]Car over 60,000km using old AFR Sensors

My car is under 60k but is a 2005 model , so maybe the sensors are due for replacing....?
Does the H6 need one for each side? I could probably do this myself as I once replaced the oxy sensor on my Levin.

[*]Very Dirty Air Filter and MAF Sensor needs cleaning (right up inside the housing and not the little bulb you see) -

My air filter is almost new and is clean. What can I clean the MAF sensor with?

[*]Poorly operating Injectors. Injectors need cleaning

Is there a fuel tank additive that works, or would I need to get a fuel injection specialist to do that properly?

[*]Very dirty Intake Header. Need professional cleaning

Does a fuel injection specialist do this?

[*]Carbon build up on the piston heads and valves, due to too much slow driving and maybe lack of service[/i

Car has been serviced at 45XXX. I can drive a bit faster I suppose...

[*][i]Leaking valves. You should have an Engine Compression test on all 6 Cylinders

I suppose this can be done at the next service

[*]Leaking Exhaust Headers

Ditto

[kleinerbastler]

@GTbee
Yes, that are all things you have to check.
But i have noticed that a "free" exhaust (200cell cats)and with Edwards hands make a huge difference. You can easily drop your consumption for about 1l/100km (with constant driving). I have fully loaded and with speedo speed 130km/h 9.6l/100km - i think not bad .

[smythie]

How short are the "mostly shortish trips"? If they are less than 15 minutes in length your consumption is refltecting the fact that the car isn't spending much time outside its "warm up" period every time it is run. That will result in much higher consumption figures than you would expect from it.

I've also seen 14+ in snarling stop/start traffic (eg King Georges road from Wiley Park to Princes Hwy in the middle of afternoon peak hour) so if you have a combination of the two 15 would be close to what I would expect.

[666]

You do indeed have a problem as the fuel usage should not be that high even with short trips.

Get you mechanic to check the usual things (air filter, injector clean, spark plugs etc) and perform a upper engine clean as recommended in the owners manual. The AFM might benefit from a clean but if it's gone the Check Engine light will come on, I think that a injector clean and upper engine clean will show a big improvement as spark plugs should last more than 47,000 Klms and issues with engine compression will show up as more serious symptoms.

Rob.

[GTbee]

Just filled up again yesterday. Latest consumption 16.4l/100.

I've been doing almost all shortish trips (10-15 mins max) lately because weather has been crap, working overtime last few Saturdays (and taking the train). Even so this most recent fuel economy is shocking. I do "rev it out" once in a while to get rid of all the bad stuff..but nothing to excess.

Until I get the car properly serviced (where I'll ask whoever does that service to look at everything in west_minist's checklist) what decent fuel injector cleaner can I use?

[thezone]

Mine got 12l/100km on the nose.

[iSpecB]

doing 14.6l/100kms....actually worse than my Q7 (12.4l/100km)!

[alessandro132]

10.5-11L/100km urban, and about 9-9.5L/100km on the highway - how are some of you others getting such high figures? Must be driving with a lead foot

EDIT: reset my trip computer and have come back with the above.