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Post by Blarno on Sept 27, 2019 14:23:31 GMT
My OBC claims that I have averaged 51mpg since purchasing the car and yet every tank so far has netted me no better than 39mpg average on calculation. I was always led to believe that BMW OBCs were pretty accurate, but either mine is completely shagged or they are not as accurate as claimed.
Any other BMW owners experience anything similar?
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Post by michael on Sept 27, 2019 14:50:54 GMT
I've never in my life done the brim to brim tests and only ever looked at the OBC to give me a ball park kind of figure. I'd expect any OBC to be out +/-3mpg but 12 is pretty massive. Are you resetting the trip on each fill? Could 51 be the lifetime average and 39 the average of that tank?
The more plausible suggestion is it's bust.
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Post by Tim on Sept 27, 2019 15:07:22 GMT
My current one usually says the average is around 48 but the calculation is nearer 43-44, so about 10% out.
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Post by Martin on Sept 27, 2019 15:12:47 GMT
Mine is around 6-7% out, the least accurate car I’ve recorded. The Golf is less than 1% out.
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Post by Stuntman on Sept 27, 2019 15:37:39 GMT
Mine's optimistic by about 5%, but it's usually within 1.5 mpg of the truth and the messages are consistent so I can rely on it from a range point of view.
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Post by Blarno on Sept 27, 2019 16:03:17 GMT
The Saab one was as close to bang on as humanly possible. If it said 48, the calculated average was always 47 at worst.
I reset the trip every fill, but didn't reset the OBC until this morning. Up to now, I've got no further than 460 miles before the light comes on. It's not due a service for another 10k, but I think the sluchbox may need a flush and fluid change pretty soon. I've not driven a vast amount of automatics - do they usually keep revs steady whilst gaining speed like you'd expect a CVT to do?
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Post by racingteatray on Sept 27, 2019 16:37:28 GMT
No idea. Sorry. Never really paid sufficient notice to work it out. Unsurprisingly being a 3.0 with an 8-spd box, it slurps fuel with gay abandon in town, but is remarkably parsimonious on a long motorway run thanks to that 8-spd box.
And you've foxed me on the revs question - no idea! But it definitely shouldn't feel like a CVT. It should feel like a normal car, just without the need to change gears yourself.
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Post by ChrisM on Sept 27, 2019 16:40:45 GMT
..... I've not driven a vast amount of automatics - do they usually keep revs steady whilst gaining speed like you'd expect a CVT to do? Only at low-ish revs briefly when the torque converter is locking up, but you shouldn't really notice a CVT-like effect. Sounds like something is awry and maybe a fluid change (and filter if there is one) will sort it, presuming it's a traditional slushmatic. |
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Post by johnc on Sept 27, 2019 16:52:28 GMT
It's absolutely not a CVT type box so I would suggest that there might be some slip somewhere requiring a bit of attention. My onboard computers have always been fairly accurate, perhaps 1 or 2 mpg out at worst. I don't bother checking the M5, I just enjoy it!
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Post by Martin on Sept 27, 2019 16:55:02 GMT
I’ve always recorded mine because I like to keep track of the stats, it’s never impacted my enjoyment or changed my behaviour.
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Post by Blarno on Sept 27, 2019 18:16:17 GMT
The slipping effect only happens at reasonably light throttle between 40 and 60 ish MPH. From startup it slushes through the first 4 gears smoothly.
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Post by Roadsterstu on Sept 27, 2019 19:59:20 GMT
The slipping effect only happens at reasonably light throttle between 40 and 60 ish MPH. From startup it slushes through the first 4 gears smoothly. I suspect this is something similar to what happens with Volvo's autos. Who makes the BMW skushers in yours? Volvo's were Aisin and it was the servo/solenoid issue, I think. The phenomenon is known as "transmission flare". A fluid change - or rather a flushing procedure, more like a series of gradual flushes and changes - is a possible cure. Certainly a fluid change might help in the short term but beyond that it might need a bit more work. The AW-55 'box in my V70 D5 was the reason I got rid when I did. I'd try a flush and fluid change first. Then see what happens. |
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Post by Blarno on Sept 27, 2019 21:37:01 GMT
It's a ZF box, 5 speed with manual mode.
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Post by Roadsterstu on Sept 28, 2019 8:19:21 GMT
It's a ZF box, 5 speed with manual mode. Whilst it might be a much better box (genuinely no idea), it could be similar causes. Try the full flush and new fluid first. |
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Post by Tim on Sept 30, 2019 9:42:23 GMT
My 2 E46 320ds only ever got below 49, indicated, during winter when fuel economy seems to naturally take a dive (also hampered by adding winter tyres).
From memory I used to get well over 500 miles between fills as well.
I'd expect the economy of the auto version to be a bit worse in general as its pre-fancy 8 speed box tech.
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