| auszookers.com https://auszookers.com/forum/ |
|
| Jimny: Increase in Fuel Use https://auszookers.com/forum/viewtopic.php?f=37&t=57235 |
Page 1 of 1 |
| Author: | matt_g [ Thu Apr 07, 2022 3:32 am ] |
| Post subject: | Jimny: Increase in Fuel Use |
Hi folks, Just wondering what the best place to investigate is - I've noticed a pretty reasonable negative change in the fuel efficiency of my 2010 Jimny (~60k km, owned since new). I have a semi regular trip I do from Noosa to Brisbane and back, I drive the same route every time. I have a pretty clear memory of It consuming about a third of a tank of U98 from full to do the round trip. Last couple of times, it used about half a tank of U98 from full for the trip. The most significant change I can think of, is new tyres. The old ones - BFG All Terrains, I think the KO series. They were the ones I had fitted to the vehicle by the dealer when I bought it (so yes, overly old tyres, that a RACQ guy suggested were "like driving on steel"). They were replaced ~6 months ago with the current version of the same tyre, the KO2. I've been running the pressures at the standard pressures recommended by the door plate (as I was advised here) IIRC 23 front, 26 rear. The marketing for the tyre describes it as being longer-lasting than the previous models, but would it be normal to experience a fairly dramatic change in fuel efficiency from just that generational tyre change (maybe they're softer rubber due to age, and have higher rolling resistance?) Or, should I ask my mechanic to look for something else - engine, exhaust etc? Any ideas / education would be appreciated. Cheers, |
|
| Author: | shep [ Thu Apr 07, 2022 7:12 am ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
If you don’t do the maintenance yourself then I would start by having a look at the air filter. |
|
| Author: | Gwagensteve [ Thu Apr 07, 2022 11:47 am ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
No, changing to new tyres (of the same size and type) won't make the fuel consumption notably worse. You can help us understand more about what's going on by using units to express economy - l/100km is the standard measure and will allow us to compare what you're getting with others. Next time you fill up, divide the litres you put in by km travelled on your trip meter expressed as hundreds. Note, your speedo will be out if you're running 215/75/15 tyres (the most common replacement size for a Jimny) so you need to correct distance travelled for that too, by about 7%. Lets say you put 35 litres in and went 325km on your trip meter. 325/100*7=22.75km so actual distance travelled = 347.75 35/3.48 = 10.05/100km. Now we have a baseline for comparison. Next, have you ever seen the check engine light come on while driving? If your route between noosa and brisbane contains quite a lot of light throttle cruising, it's possible the oxygen sensor is playing up. This can cause the car to run rich at cruise and consume more fuel. However, it would normally throw a check engine light, as would pretty much any sensor if they were at fault. Items that could cause an issue that won't throw a check engine light include: Failing catalytic converter. These can break up and restrict the exhaust. Air filter as per Shep's comment - but it would have to be very, very dirty to significantly effect economy. Failing coil pack Fouled fuel filter (these are in-tank in a Jimny as far as I am aware. dragging brake/wheel bearing (check there isn't one wheel that feels hotter than the others after a long drive) A left field fault could be a failing knock sensor. I'm not sure if this would throw the check engine light on or not, but the reason I mention it is that you specify you're running 98 octane. I wasn't aware the M13 was knock sensed but as it is, if it's mapped for 98 octane it (should) be advancing the timing to exploit 98 octane and by watching the oxygen sensor, backing the fuelling trim out appropriately. If the knock sensor is failing, it might revert to the 91 octane map so you're using more fuel to do the same job. If your mechanic has a scan tool it might reveal something if it's associated with sensor function, otherwise its likely to be one of the things I've mentioned. |
|
| Author: | matt_g [ Thu Apr 07, 2022 1:30 pm ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
Thanks for the replies folks. I did a bit of math (so get the safety tape out) - it's a round trip of (working it out on mapping software by putting my exact route in): 278km So, I'm using half a tank ~20L to do that now, whereas before I'm pretty sure I was doing it in around a third ~13.3L... 20/2.78 = 7.19/100km (the official figure is 7.3/100 combined cycle) 13.3/2.78 = 4.8/100km... does that seem unreasonably efficient, even for a mostly highway run? I must be mis-remembering - but I'm so sure the needle on the fuel gauge was reasonably into the full half when I used to get back from these trips, and now it's dead on the centre. Again, to add another "this is subjective memory so may not be very valid"... *if* I felt the car was down on power on a local steep hill, I was having to push the accelerator a bit harder, bleeding more speed (80 zone at the start of the hill, I end up at 50 in 3rd gear if I'm lucky by the time I'm at the top)... would that point somewhere more specific? I've tested the speedo against my (dedicated) GPS, and it seems to read pretty accurately at 60 / 80 / 100, which makes me think it would have been reporting over-reporting on the factory tyres? There haven't been any check engine lights... I did notice the rear bumper was noticeably warm to touch after a leg of the trip, which is something I've never noticed (or looked for) before, but the muffler is right behind it, so I guess that's normal? |
|
| Author: | Gwagensteve [ Thu Apr 07, 2022 2:39 pm ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
There is no way a Jimny can achieve 4.8l/100km on the highway. The long story is there's too much drivetrain loss, the engine is turning too fast and the car isn't aerodynamic enough. 7.12l/100km is fantastic fuel economy and as good as you could ever expect A jimny won't see the huge difference in economy between urban and highway use because it's not aerodynamic. Aerodynamic cars can be very efficient on the highway compared to around town because it takes a lot more power to accelerate a slippery car than it does for it to maintain speed, whereas a car with poor aerodynamics takes a lot of power to push through the air at speed. It's not out of the question the speedo is around 5% low on standard tyres - that's common practice, so if it's reading spot on now that's great and one less thing you need to take into account. I can't comment on if the car is down on power. If you want to investigate any of the things that have been suggested you may see a benefit, but if you're paying someone to check this stuff it can get quite expensive with an uncertain outcome. |
|
| Author: | matt_g [ Thu Apr 07, 2022 2:52 pm ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
Thanks for the additional info - at least it confirms for me that the current consumption isn't unreasonable... I'll keep an eye on it more closely (though "keeping an eye on it" is probably what made me think I noticed something wrong), and mention it to the mechanic at the next service. Cheers, |
|
| Author: | Gwagensteve [ Thu Apr 07, 2022 3:22 pm ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
I always monitor economy at every fill by using the trip meter, even in my cars that have fuel economy displays. It's just force of habit. I don't write it down or keep spreadsheets or whatever, just a quick check that everything is about normal for the way I'm using the car. Interestingly, all three of my cars get almost identical economy on the highway - that's an early diesel discovery, (9.6l/100) FG XR6T ute (10.0l/100km) HSV GTS R (about 9.8l/100km) All three weigh about the same, the ute being the lightest. The difference is the discovery gets 9.6l/100km around town too, vs the falcon about 12.5-13.5l/100km and the commodore about 18-21l/100km. That's a reflection of how much more throttle the discovery needs to hold speed compared to the other two. Maybe put a few more tanks through the car using the trip meter to check actual economy and see how it's tracking. There may well be a small issue but based on the economy you're reporting it's not a huge issue. |
|
| Author: | sideways [ Fri Apr 08, 2022 1:36 am ] |
| Post subject: | Re: Jimny: Increase in Fuel Use |
Gwagensteve wrote: I always monitor economy at every fill by using the trip meter, even in my cars that have fuel economy displays. I think this is important to do. My Discovery always used 15-20% more fuel than the readout says. By contrast my Statesman uses about 5% less than the dash tells me. |
|
| Page 1 of 1 | All times are UTC + 9:30 hours |
| Powered by phpBB® Forum Software © phpBB Group https://www.phpbb.com/ |
|