Would a change of very old ( possibly original ) autobox fluid make a big difference to mpg?
Im not entirely sure of the role the fluid plays in the transmission of power to the wheels.
I ask because since my cars service on weds, its become dramatically lighter on fuel.
I know by a certain mark on the fuel gauge how well its doing and usually by the time its 3 bars from the red, its got about 60 miles to go and it was on this mark when the car went into the garage. It went a full 40 miles further than usual which is a big hike on a 25 litre fill up.
The car does feel much better in that it changes gear more smoothly, kickdown is more positive and it seems to gather speed with far more ease than before. It also seems far smoother in terms of vibration under load.
Could the fresh fluid really be making all that difference?
|
>> Would a change of very old ( possibly original ) autobox fluid make a big
>> difference to mpg?
No
>> The car does feel much better in that it changes gear more smoothly, kickdown is
>> more positive
That could be the fluid.
and it seems to gather speed with far more ease than before. It
>> also seems far smoother in terms of vibration under load.
Add this to the MPG improvement, and I would say it caused by a new air filter which you said was changed, were the plugs changed as well?
>> Could the fresh fluid really be making all that difference?
>>
|
Havent done the air filter yet, when did I say id changed it? ( I may well be going senile ). Havent changed plugs. Its got new front tyres but only since yesterday. PAS fluid was changed but cant see that being such a huge power drain.
Im genuinely perplexed.
|
|
Ah right I thought you had, I now see that you removed the filter, and in doing so have dislodged all the sealing foam? the air filter is leaking air round it I assume.
|
Foam was just part of the two mountings for the airbox, not part of the air filter ( I presume the foam was to isolate it against the vibration of the engine ), airfilter itself hasnt been out, you can remove the intake without distrubing the air filter - its abit grubby though so ill be changing it when I can find one!
Come next Friday ill know how dramatic the change has been as the jump has been 5 mpg over the previous week ( 39.5, 38.5, 43.5 ), so with the first full tank since its service ill know if theres consistancy. Ive not driven it any different either, nor especially carefully.
I dont know how much effect is down to the car loosening up after 5 months on a garage forecourt. As someone who often buys low milers, I do sometimes get a jump after a few weeks, but usually gradual. Doing 250 miles a week certainly blows out any cobwebs on something that previously did less than half that.
Last edited by: FoR on Fri 27 Jan 12 at 13:50
|
|
Its the work of some almighty being then.
|
Im not complaining ;-)
The Combined figure is 41.5 mpg so Im happy to beat that. If I can top 46 then thats the Extra Urban which I can usually manage if I try.
|
I presume the new fluid will be more viscous than the old stuff, so maybe there's less slippage in the torque converter, thus better engine->transmission energy transfer.
Or it's the baby Jeebus at work.
|
That was my thought tbh, the fluid that came out was prob a decade old and the car does spend alot of time in top gear at slow speeds such is the way its set up. Thats where you notice the difference as at say 25 mph the pickup is far stronger.
May also be that it requires less throttle, I do feel Im lighter on the throttle to maintain the same speeds as before esp up hills etc.
|
The old stuff may have been burnt and a fresh new transmission filter will pass the oil around the valves much quicker making those gear changes smoother and more responsive.
Less throtle as your doing is the key to the economy.
Fluid change & filter every 60k or 5 years and you won't have any bother with it.
|
>> Would a change of very old ( possibly original ) autobox fluid make a big
>> difference to mpg?
>>
>> The car does feel much better in that it changes gear more smoothly, kickdown is
>> more positive and it seems to gather speed with far more ease than before. It
>> also seems far smoother in terms of vibration under load.
>>
>> Could the fresh fluid really be making all that difference?
>>
Yes it could.
|
>> Yes it could.
No it cant - not enough to notice.
|
|
Its a very small engine with low torque and a power-sapping gearbox - might be more noticeable than on something with a V8.
|
Not enough for a noticeable change in fuel consumption of the level you are talking about.
Its likely to be a subconscious change in driving style.
|
Or an inadvertent Italian tune-up in the past couple of hundred miles if previous owner was a dawdler.
Or you've inflated the tyres correctly.
etc.
|
The change in the way the power came in was definately after the service, it was light and day as before it felt so laboured up hills. Its only 54 bhp so it doesnt take alot to affect the usefulness of that power.
Ive seriously not driven it any different to before. I drive the same roads at much the same speed every day. I tried driving really economically in a way which worked before and that was when I got the 38 mpg so I stopped trying. The week before id not made any effort.
I think if at the next fillup its up around the high 40's then for sure something has 'flipped' with the car.
|
>> Ive seriously not driven it any different to before.
I did say subconsciously. You know the fluid was changed, it feels different, you could have altered your right foot to suit.
If it had 4 horsepower I might think it could make a difference. Otherwise its not a direct cause of your jump in consumption. Its just being driven differently is all.
|
As Bigtee mentions, the new oil will be flowing better through the valves etc , but more importantly, the torque converter will be operating more efficiently.
As hydraulic oil ages, viscosity lowers, and it also becomes subject to increased Cavitation (foaming).
If one thinks about suspension dampers (shock absorbers) as they age, they begin to lose that ability to 'damp' allowing the suspension to oscillate.
That is a well know fact, and purely fitting new dampers improve handling no end. (highlighting how poor the old ones were at their job)
In a torque converter, the drive is passed by the fluid, if the fluid suffers Cavitation, then power losses will happen.
|
>> In a torque converter, the drive is passed by the fluid, if the fluid suffers
>> Cavitation, then power losses will happen.
which would be noticed in the form of "slipping" by the driver,
|
Which was probably happening - slipping is usually felt at low revs and Stu did mention better uptake of gears since the change.
|
>>
>> >> In a torque converter, the drive is passed by the fluid, if the fluid
>> suffers
>> >> Cavitation, then power losses will happen.
>>
>> which would be noticed in the form of "slipping" by the driver,
>>
It has (retrospectively) been....
''The car does feel much better in that it changes gear more smoothly, kickdown is more positive and it seems to gather speed with far more ease than before. It also seems far smoother in terms of vibration under load.''
|
>> >>
>> >> >> In a torque converter, the drive is passed by the fluid, if the
>> fluid
>> >> suffers
>> >> >> Cavitation, then power losses will happen.
>> >>
>> >> which would be noticed in the form of "slipping" by the driver,
>> >>
>>
>> It has (retrospectively) been....
>>
>> ''The car does feel much better in that it changes gear more smoothly, kickdown is
>> more positive and it seems to gather speed with far more ease than before. It
>> also seems far smoother in terms of vibration under load.''
seems to gather speed with far more ease than before is the only slipping related statement.
I would however have said, "the engine revs rise but its not going anywhere - it feels like its slipping"
Last edited by: Zero on Fri 27 Jan 12 at 20:23
|
>> >> ''The car does feel much better in that it changes gear more smoothly, kickdown
>> is more positive and it seems to gather speed with far more ease than before.
>> It also seems far smoother in terms of vibration under load.''
>>
>> seems to gather speed with far more ease than before is the only slipping related
>> statement.
>>
>> I would however have said, "the engine revs rise but its not going anywhere -
>> it feels like its slipping"
>>
As Bigtee and myself have said, the new oil will be flowing through the valves better as well.
Both the torque converter and the gearbox itself, will be operating more efficiently, thus showing a larger net improvement.
|
>> Both the torque converter and the gearbox itself, will be operating more efficiently, thus showing
>> a larger net improvement.
Not to the levels that stu has reported.
|
>>
>> >> Both the torque converter and the gearbox itself, will be operating more efficiently, thus
>> showing
>> >> a larger net improvement.
>>
>> Not to the levels that stu has reported.
>>
>>
OK, reading back I see Stu is reporting 5MPG better.
I agree that IS a big jump, but it is possible, a freshly serviced car, brakes that as Stu said, may have loosened up after the car standing for months, and maybe weather conditions will all add up.
|
>> OK, reading back I see Stu is reporting 5MPG better.
>> I agree that IS a big jump, but it is possible, a freshly serviced car,
>> brakes that as Stu said, may have loosened up after the car standing for months,
>> and maybe weather conditions will all add up.
ALL of that together, I agree could add up.
|
It was certainly laboured. It didnt slip in an omg way but if you put your foot down at say 30, not alot happened - the revs rose a little but the actual speed gain was gradual. I only realise it now because the change has been so significant.
Its not a quick car anyway so I just assumed it was an asthmatic performer. At lower revs, say 1500-3000 it pulls much stronger, this is the range its in about town, nearly always in top gear and under the highest load.
You come off most roundabouts still in top, it rarely changes down from that gear but this is prob 1500-2000 rpm at 15-20 mph. Its under those circumstances that a squeeze of the throttle actually results in a reasonable gain in speed which previously didnt happen.
Last edited by: FoR on Fri 27 Jan 12 at 20:37
|
|
if you feel the road speed is rising now more in proportion to number of revs - it may well have been slipping. You would have noticed it on the rev counter, the revs may have dropped to meet road speed, more than the other way round.
|
I certainly dont feel like im riding the car so hard to maintain progress.
Theres not much change above 45mph but below that there certainly is. I notice it especially on a hill near my home where I hit the bottom at 45 and before it would slip back to 35 until the top, now it gets up to 45 and stays there.
The engine note is lighter too, like its under less load which presumably means im subconsciously using less throttle than before.
Im glad of the improvement thats for certain.
|
>>I presume the new fluid will be more viscous than the old stuff, so maybe there's less slippage in the torque converter, thus better engine->transmission energy transfer.
The torque coverter works via the transfer of fluid momentum rather than via viscous drag.
The reasons for changing auto transmission fluids are much more to do with refreshing the friction modifiers in the additive pack, and for cleaning out of suspended carp than for gross changes in fluid viscosity.
|
:-)
Can always rely on me having no clue what you mean, but it sounds right.
|
I'd say you've just inadvertently given the car a bit of an Italian tune-up Stu. Maybe it had also been sitting unsold on a forecourt for months?
FWIW, I'd have thought that the number of gears in the autobox is a bigger indication of better economy. My A3's 6-speed auto is proving to be 15% more economical than the 4-speed KIA that preceded it. Both 2litre petrols, but the Audi weighing a good 100+KG more too...
|
Just for a test if the transmission was pressure tested with old oil the readings will be low and fresh oil added the pressure would be higher, the key is also to get the old stuff out of the torque converter.
The old mercs had a drain plug fitted perfect in the t/c, and the filter catches the worn friction plates which are black fragments.
Can't beat fresh oil just like in the engine.
|
Autobox fluid/mpg - Zero
