mpg

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philwxh
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mpg

Postby philwxh » Sun Feb 24, 2008 5:57 pm

hi can anyone tell me what sort of mpg i will get on a 2003 2 ltr megane only going to use it around town and short journeys to work.

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Postby Jonault » Sun Feb 24, 2008 7:57 pm

Have a trawl through here:

https://www.meganeownersclub.co.uk/forum ... php?t=5159

There might be some figures for the 2.0ltr amongst the rest.
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IainMW
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Postby IainMW » Mon Feb 25, 2008 12:27 pm

philwxh

Big engines and short journey's are not a good combination for decent MPG figures.

Why a 2.0ltr if you are only doing short journey's

Have you considered a Diesel?
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Ray
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Postby Ray » Mon Feb 25, 2008 7:21 pm

wouldn't a diesel be just as bad for short journeys and town driving? :?
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walibe
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Postby walibe » Tue Feb 26, 2008 9:04 am

Surely the 1.4 is the best engine for this situation?
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IainMW
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Postby IainMW » Thu Feb 28, 2008 1:28 pm

I would have said a 1.5dCi would be best suited.

Short journeys mean Petrol engines don't warm up sufficienty hence they always run rich and use more fuel)

A petrol engine draws air and fuel into each cylinder, it's compressed and ignited by a spark and the compressed mixture explodes in the cylinder forcing the piston back down, but the fuel also cools the cylinder walls and causes a drop in efficiency. Remember that a petrol engine is only approximately 27% thermally efficient.

Diesel's only draw air into the cylinders, this is compressed and Diesel fuel is injected in to the hot compressed air this then burns, it does not explode.

The Diesel engine has a theoretical thermal efficiency of 75% (Rudolf Diesel calculated and designed this in 1892!!!)

In practice this come down to about 37-42% in terms of modern Diesel car engines.

:cool:
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Postby AlexB » Wed Mar 05, 2008 8:07 pm

Iain, it is not about cooling the cylinder wall. Then, don't forget that SI engines come in different flavours: Otto, Atkinson, Miller cycle... I drove a Prius once -- it was pretty efficient.
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Postby wanda » Fri Mar 07, 2008 11:49 am

Here is some evidence to show that it can be done. Clio 1.5dci 105bh

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IainMW
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Postby IainMW » Fri Mar 07, 2008 2:31 pm

In my limited understanding of Physics a petrol engine can never be as efficient as a Diesel engine

There's lots on the web about this; two little snippets

https://www.cleangreencar.co.nz/page/prius-petrol-engine
https://www.antonine-education.co.uk/phy ... ngines.htm

As for efficient Clio's, my wife's old 1.5dCi 80 would regularly achieve 60mpg + running around town and over 70mpg on longer runs. The highest I ever got it to was 86.3mpg but I was driving like a granny :lol:
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Postby AlexB » Sat Mar 08, 2008 12:43 am

True. Diesels also feel great with high torque in low revs, which explains why I bought one. I, actually, did not like that Prius. It felt boring after I got used to the gadgets (the whole Prius being a big gadget). It was also noisy under acceleration.
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72uoba
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Re: mpg

Postby 72uoba » Wed Mar 19, 2008 8:42 am

Depends how short the journey is. Diesels take far longer to reach normal operating temperature.

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IainMW
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Re: mpg

Postby IainMW » Wed Mar 19, 2008 10:07 am

72uoba wrote:Depends how short the journey is. Diesels take far longer to reach normal operating temperature.


Yes because they are far more thermally efficient! But most should be upto operating temperature within 4-5 miles. A petrol is not much quicker and on a short journey runs rich wasting even more fuel and potentially shortening the life of the CAT.
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72uoba
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Re:

Postby 72uoba » Wed Mar 19, 2008 10:33 pm

IainMW wrote:Short journeys mean Petrol engines don't warm up sufficienty hence they always run rich and use more fuel.


I was referring to this statement that you made. Petrol engines reach normal operating temperature (and inherently, efficiency) more quickly than diesel engines (their overall thermal efficiency is a different argument). Therefore, for many short (possibly very short journeys), a small petrol engine maybe makes a more sensible choice.

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DaveP
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Re: mpg

Postby DaveP » Sat Mar 29, 2008 2:02 pm

In answer to the original question (rather than the following debate about why you shouldn't get a 2.0l petrol!), our 2.0l petrol CC does about 26-27mpg doing short journeys mostly in traffic, on a run it'll manage 34-35mpg.
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