does yours do this?

[Šįk]

once i have a full tank, my car seems to gobble the petrol fairly quickly to the half way point. on the half way point for aagggesss, then suddenly starts to drop again after that :S just wondered if any1 else's did this? (i have a ph2 172 for the record)

btw what speed/rpm do you guys sit at for best fuel comp? i usual sit at 80mph ~4k rpm, i think sitting at anymore means the fuels get major gobbleatroned!

 

[Craig]

i think alot of them do. mine does it

 

[my172]

Yeah mine has a habbit of doing this also!

 

[Redler]

haha i thought this was just mine, it does exactly the same! Even when driving carfully!
With regards to motorways i try and sit at 4k, feel the same as you!

 

[1PBY]

well 56mph is the most economical speed to sit at but it will take you ages to get anywhere. sitting at 70 instead of 80 will save you alot of pertrol though as it will lower the revs away from the magic 5k!!!i get around 36mpg at 80mph and about 42mpg at 70mph. just depends on how much of a hurry your in!!!lol

 

[caeteez]

Mine does this too, and its just a 1.2. I wonder if its something to do with how it measures the fuel, or if its just psychological. I think you tend to look at the fuel level more as it gets nearer the bottom, so maybe it seems to take longer?

 

[scott1205]

the last half of my tank seems to last much longer than the first

 

[gaz44]

well 56mph is the most economical speed to sit at but it will take you ages to get anywhere. sitting at 70 instead of 80 will save you alot of pertrol though as it will lower the revs away from the magic 5k!!!i get around 36mpg at 80mph and about 42mpg at 70mph. just depends on how much of a hurry your in!!!lol

Think about what you just said. Surely, by your logic, lowering the revs from 56mph to say, eh....45mph will increase fuel even more?! As long as you're not pinking the engine.

 

[The Boosh!]

Think about what you just said. Surely, by your logic, lowering the revs from 56mph to say, eh....45mph will increase fuel even more?! As long as you're not pinking the engine.

No you are wrong

56 mph IS the most economical speed you can sit at on the motorway.

something to do with combustion rate/speed reaching its equilibrium at that speed.

 

[Ali]

yep!

Williams was funny! 250miles to 1/4 of a tank. Then 100 for the other 3/4! lol Drops like a stone. Spiders SOOKING ma fuel!

 

[D4N13L]

mine does too, it also hangs on empty for ages before the light comes on

 

[Tom@JMS]

the tank is a trapeze shape, hence it drops quickly at the start end end but does hand about in the middle.

 

[Redler]

the tank is a trapeze shape, hence it drops quickly at the start end end but does hand about in the middle.

That would explain alot :rasp:

 

[markhinton]

You'll find that the sending unit is non-linear, this is partly to do with the shape of the tank but more to do with the fact that a petrol sender unit reads hyperbolically.

 

[st3ve]

Can't really collaborate on this as I rarely fill my tank, only do it for long journeys and it seems normal to drop fairly quickly at motorway speeds but what I will say is whenever the needle gets down to 1 bar I have to put petrol in otherwise it won't start if I am parked on a slight incline. So it's pretty much pointless the red bar at the bottom being there.

 

[The Seer]

On any long hauls I simply sit a 56-60 mph. Not sure if the consumption is that much better than 70 mph???:S

 

[m4rkie23]

prob the shape/size of the petrol tank aint it? mine does it too

 

[Vish]

On any long hauls I simply sit a 56-60 mph. Not sure if the consumption is that much better than 70 mph???:S

My Pass Plus instructor told me you use a 1/3 more fuel driving at 70 than 60. Or a 1/3 less driving at 60 than 70. It was one of them.

No idea if it was true or not, but think he was hinting at me to slow down lol

And to the OP. I find I can get more miles on the second half of a tank than the 1st.

 

[JJS1979]

Yeah mine dose this as well...

 

[markhinton]

My Pass Plus instructor told me you use a 1/3 more fuel driving at 70 than 60. Or a 1/3 less driving at 60 than 70. It was one of them.

No idea if it was true or not, but think he was hinting at me to slow down lol

He's talking absolute b****cks!

You can't be so specific with it anyway, it depends on the gearing, weight and aerodynamics of a car among other aspects. All cars are different (unless we're talking about the same model of car).

Of course you'll use less petrol travelling at a lower speed, that's a given. There's less downforce being created, less drag and the engines not having to do as much work to keep a constant speed. But specifically 1/3 of petrol? lol!

 

[coatesy]

well 56mph is the most economical speed to sit at but it will take you ages to get anywhere. sitting at 70 instead of 80 will save you alot of pertrol though as it will lower the revs away from the magic 5k!!!i get around 36mpg at 80mph and about 42mpg at 70mph. just depends on how much of a hurry your in!!!lol

is that 1 of the reasons lorrys are restricted to 56mph?

 

[markhinton]

is that 1 of the reasons lorrys are restricted to 56mph?

It's mainly down to the speed the government sees fit for lorries to travel at. But I guess this might be a deciding factor in it, yeah!

 

[m4rkie23]

yes

 

[maz172cup]

its a 2.0 size so it will do - im does but i do rip the sh!t out of it (172cup)

 

[Vish]

He's talking absolute b****cks!

You can't be so specific with it anyway, it depends on the gearing, weight and aerodynamics of a car among other aspects. All cars are different (unless we're talking about the same model of car).

Of course you'll use less petrol travelling at a lower speed, that's a given. There's less downforce being created, less drag and the engines not having to do as much work to keep a constant speed. But specifically 1/3 of petrol? lol!

I assumed he meant rough figures, 1/3 in general. I thought a 1/3 was a bit of an exaggeration though so I stuck to 70 anyway.

 

[edde]

well 56mph is the most economical speed to sit at but it will take you ages to get anywhere. sitting at 70 instead of 80 will save you alot of pertrol though as it will lower the revs away from the magic 5k!!!i get around 36mpg at 80mph and about 42mpg at 70mph. just depends on how much of a hurry your in!!!lol

56 isn't the most efficent speed it depends on loads of things the original 300SL merc were at that speed as it was released in an mpg vs speed graphs in the owners manuals

You'll find that the sending unit is non-linear, this is partly to do with the shape of the tank but more to do with the fact that a petrol sender unit reads hyperbolically.

the system does compensate for this but its the tank shape and tolerances which give this fuel gauage issue

On any long hauls I simply sit a 56-60 mph. Not sure if the consumption is that much better than 70 mph???:S

it is by a fair old bit

 

[DMS]

Yep, mine does this. I think I mentioned it in a different thread a while back.
First third of a tank goes in about 50 miles or so, then the middle third of the tank seems to last the rest of the week (about another 200 or so miles) before it quickly gets into the red.
I tend to trust the trip computer to tell me how much fuel I've got left now. Even if the needle suggests a third of a tank has gone, it still says I've got about 300 to 350 miles worth left.

As per the posts on fuel consumption, I would tend to agree that the most economical speed to drive at is about 55mph on flat roads. On motorways I tend to find 70mph is still very economical though.
My car drinks juice on twisty roads though... something to do with my right shoe apparently...

 

[RDH]

Digital fuel guage ftw.

 

[Rossy197]

I dont really notice tbh... fill up when needed, Just been to k-Tec and back (roughly 195 miles) and i was sitting nye on 100 all the way.. used just over half a tank. dunno if thats good or bad ??

 

[mcphee197]

If i tank my 197 the needle hardly moves for the first have and it makes me happy. The second half is a different story however.

 

[Kemixx]

Mines the other way round. First half goes down slowly then the second is gone in no time.

 

[Ben10]

Right surely going at 30mph in 5th gear, you will use the same arount of petrol as travveling at 60mph in 5th gear? lets say you cover 30 miles - your car will be using petrol for a full hour to get to the destination at 30mph, whereas at 60mph, your car will be using maybe twice as much fuel for half the time? so technically should it not matter?

somebody please correct me with fancy words

and my digital fuel gauge is showing 1 bar - yet says i have 80 miles left (the rest of my almost full tank went in around 100 miles) and for a 1.2, my previous clio seemed to go last longer on a tank. should there be a difference between the to cars? this one is a mk2 ph3, last one was a mk2 ph2.

cheers

 

[Eckascliovalver]

I dont notice this as i only put 15L in at a time. Weight of petrol = less fast cup

 

[kevin.s]

could be something to do with the car being slightly heavyer with a full tank but i know what you mean mine does it too.

 

[Ex-User (19928)]

No you are wrong

56 mph IS the most economical speed you can sit at on the motorway.

something to do with combustion rate/speed reaching its equilibrium at that speed.

If you say so.