Auto or manual mpg

man of kent · 14th November 2011, 08:15

Autos do use more fuel but when the auto has a lockup on the top gear why is the mpg worse at motorway speeds?. Could it be the transmission ratio on the auto is lower?

Back in the 80's I had a number of Carltons and the auto on the motorway was more econumical.

AngryDog · 14th November 2011, 09:47

How long do you have? so many things affect fuel economy.

Also, the Auto has a slightly lower top speed, could be doing a few more revs at motor way speeds that could affect it.

COLVERT · 14th November 2011, 10:23

How do you know they have a lockup on the top gear ???

David3807 · 14th November 2011, 11:42

Quote:

Originally Posted by COLVERT

How do you know they have a lockup on the top gear ???

Cos you can usually feel it engage and the revs drop by 100 or so rpm - at least that happens on my KV6s

Simon.h · 14th November 2011, 16:43

In general terms a manual will always, in theory, be more economical than an automatic. A manual transmission provides a more direct link via the manual clutch from the engine to the wheels while the automatic relies on oil pressure and a fluid flywheel as a clutch between the engine and transmission to supply the drive. There is always a loss of energy because of the automatic set up which makes the manual better regarding fuel consumption.

wutang · 14th November 2011, 17:03

The Auto, (in the 2.5 V6.) actually revs lower than the manual once the torque converter locks up so in theory the mpg should not be much worse, possibly a little better.

the problem is that it is very easy to unlock the auto box with very gentle presure on the loud pedal. so to actualy cruise in top with the lock on is quiet difficult, even using cruise does not really help as the minute the brain of the system demands more power (going up hill for example.) you will see the revs rise without the gear changing.

Richard

Simon.h · 14th November 2011, 17:08

A auto v a 190, well on a motor run the auto will be better as the 5 gear on my 190 has the engine revs far to high (at 70mph its just over 3000rpm).

wutang · 14th November 2011, 21:26

Quote:

Originally Posted by Simon.h

A auto v a 190, well on a motor run the auto will be better as the 5 gear on my 190 has the engine revs far to high (at 70mph its jut under 3000rpm).

Whereas my auto is at about 2200rpm at 70.

bl52krz · 14th November 2011, 22:32

One word:- clutch slip in effect. Sorry ,thats four. Never was good at maffs.

James.uk · 15th November 2011, 00:02

I seriously doubt the cars mpg are any diff in top gear, what make the op think they are?

Top speed is the same for both, final gear ratio is the same on both, so why would mpg be diff??

2200 revs = 70 mph on my cars clock..

...

14th November 2011, 08:15	#1
man of kent Loves to post 75 tourer auto diesel Join Date: Nov 2010 Location: Nordelph, nr Downham Market Posts: 419 Thanks: 0 Thanked 0 Times in 0 Posts	Auto or manual mpg Autos do use more fuel but when the auto has a lockup on the top gear why is the mpg worse at motorway speeds?. Could it be the transmission ratio on the auto is lower? Back in the 80's I had a number of Carltons and the auto on the motorway was more econumical.

14th November 2011, 09:47	#2
AngryDog Posted a thing or two MG ZT CDTi 116+ Join Date: Jul 2011 Location: Hull Posts: 1,014 Thanks: 0 Thanked 0 Times in 0 Posts	How long do you have? so many things affect fuel economy. Also, the Auto has a slightly lower top speed, could be doing a few more revs at motor way speeds that could affect it. __________________ [SIGPIC][/SIGPIC] ZT 116+ - ChipMyCar Remap - Synergy 2

14th November 2011, 16:43	#5
Simon.h This is my second home Previously owned- MG ZT V6 160 Y plate Lpg, MG ZT 190 2003 In Rare Celestial Factory Ordered Lpg MG Join Date: Mar 2010 Location: Calne Posts: 4,531 Thanks: 8 Thanked 116 Times in 108 Posts	In general terms a manual will always, in theory, be more economical than an automatic. A manual transmission provides a more direct link via the manual clutch from the engine to the wheels while the automatic relies on oil pressure and a fluid flywheel as a clutch between the engine and transmission to supply the drive. There is always a loss of energy because of the automatic set up which makes the manual better regarding fuel consumption. __________________ Previously owned- MG ZT V6 160 Y plate Lpg, MG ZT 190 2003 In Rare Celestial Factory Ordered Lpg MG ZT 190 2004 lpg

14th November 2011, 17:08	#7
Simon.h This is my second home Previously owned- MG ZT V6 160 Y plate Lpg, MG ZT 190 2003 In Rare Celestial Factory Ordered Lpg MG Join Date: Mar 2010 Location: Calne Posts: 4,531 Thanks: 8 Thanked 116 Times in 108 Posts	A auto v a 190, well on a motor run the auto will be better as the 5 gear on my 190 has the engine revs far to high (at 70mph its just over 3000rpm). __________________ Previously owned- MG ZT V6 160 Y plate Lpg, MG ZT 190 2003 In Rare Celestial Factory Ordered Lpg MG ZT 190 2004 lpg Last edited by Simon.h; 15th November 2011 at 15:01..

14th November 2011, 22:32	#9
bl52krz This is my second home Rover 75 cdt club + Rover 2.5 KV6 Conni SE Join Date: May 2008 Location: Birmingham Posts: 11,387 Thanks: 6,587 Thanked 2,262 Times in 1,729 Posts	One word:- clutch slip in effect. Sorry ,thats four. Never was good at maffs. __________________ Great Barr, Birmingham.

14th November 2011, 10:23	#3
COLVERT This is my second home R75 Saloon. Join Date: Feb 2009 Location: France/or Devon. Posts: 14,003 Thanks: 3,851 Thanked 2,167 Times in 1,816 Posts	How do you know they have a lockup on the top gear ???

14th November 2011, 17:03	#6
wutang Posted a thing or two Rover 75 2.5 auto (LPG) & mg tf 160 Join Date: Nov 2006 Location: Dartford Posts: 1,124 Thanks: 5 Thanked 39 Times in 36 Posts	The Auto, (in the 2.5 V6.) actually revs lower than the manual once the torque converter locks up so in theory the mpg should not be much worse, possibly a little better. the problem is that it is very easy to unlock the auto box with very gentle presure on the loud pedal. so to actualy cruise in top with the lock on is quiet difficult, even using cruise does not really help as the minute the brain of the system demands more power (going up hill for example.) you will see the revs rise without the gear changing. Richard

15th November 2011, 00:02	#10
James.uk Passed Away 2002 Pale Blue. Rover 75 CDTi Connoisseur auto. 170K miles Join Date: Dec 2008 Location: Near the M67. Posts: 14,509 Thanks: 199 Thanked 585 Times in 397 Posts	I seriously doubt the cars mpg are any diff in top gear, what make the op think they are? Top speed is the same for both, final gear ratio is the same on both, so why would mpg be diff?? 2200 revs = 70 mph on my cars clock.. ...