I've received a lot of questions with regard to how to improve MPG, so I've tried to document this as clearly as possible below
Engine
Often dodgy MPG is an early sign of things not right in the engine department, therefore it makes sense to keep the engine and transmission well maintained. Regular engine oil and air filter changes are an easy way to keep on top of the engine health and maintain good fuel consumption, thus keeping those running costs low
Please be aware of the fact that an engine will consume a LOT OF FUEL when starting the engine from cold - this is something that cannot be avoided but CAN BE minimised to ensure the cold start does not consume more fuel than absolutely necessary. Avoiding regular short journeys is the key factor but if unavoidable then try to time your start ups so that you make your short trip with the engine warm from a previous outing or something.
Don't let the engine just idle until heat is built up... Remember
when you're idling your doing 0 MPG so it's costing you to cover absolutely no distance at all!
Similarly, do not race the engine to build up heat quicker. Best mpg is achieved by being extra cautious and making use of very light throttle inputs use during warm up.
Accelerating & Torque
Torque is the pulling force you observe when accelerating i.e. when you're pushed into your seat. And, as you'll probably feel, this force varies throughout the engine rev range.
As a very very rough indication, an engine is at it's highest efficiency where the engine develops peak torque. Therefore attempt to maintain your revs around your peak torque figure when accelerating up through the gears - the exception is the VTS/GTi engine (1.6 16v) where the peak torque figure is stupidly high in the rev range and not really a sensible figure to reach for gradual acceleration routines -
for VTS/GTi owners, aim for shifts around 3000-3500 rpm
Peak Torque:
1.0 – 3600rpm
1.1 – 3800rpm
1.4 – 3400rpm
1.5D – 2250rpm
1.6 – 3000rpm (Mk1)
1.6 – 3500rpm (Mk2)
1.6 16v – 5200rpm
Cruising
When cruising, for instance in 30, 40, 50, 60 and 70 mph limits, use the highest possible gear
without labouring the engine i.e. making it judder or generally straining it. On level roads 30mph in 5th shouldn't be a problem, if it's an uphill stretch of road you may need to downshift to 4th or even 3rd to main speed without labouring the engine - so choose your gear accordingly. If you're accelerating up to next speed limit, say when exiting a town/residential area, again try to VERY slowly increase the speed (which again should be achievable in 5th for most) to achieve best mpg.
Decelerating
When decelerating, avoid using the brakes, instead allow the car to slow naturally by using engine braking. This method is MORE efficient than taking the car out of gear and coasting as well as being much safer. During coasting, fuel is still injected into the engine to keep the engine idling. Whereas when the car is left in gear the momentum of the car maintains the engine revs and therefore far less fuel is used. NOTE, Saxo’s still inject some fuel into the engine under engine braking, unlike modern engine where virtually no fuel is injected.
MPG 'Boosters' - Super Fuels & Off-The-Shelf Fuel Additives
Fuel additives and Premium fuels are increasingly popular amongst Saxo Enthusiasts – some offer octane boosters or higher octane’s to boot, as well as specialised detergents that clean the fuel system and aid combustion. Premium fuels such as V-Power, BP Ultimate, Total Excellium etc, although offering fuel rated at 98/99RON as well as a host of additional chemicals aiding combustion and fuel system cleanliness, are limited in their benefits for a Saxo. The Engine Management System does not have a sufficient operating envelope to fully utilise the properties of these fuels. Some members report benefits of using premium fuels whilst others do not.
First things to be aware of are:
The standard Saxo ECU is capable of adjusting ignition timings up to 98RON (according to model documentation) meaning that whilst the full abilities of 99RON Premium Fuel can't be achieved, there is still a margin where the engine can
make use of the benefits that come with using a higher octane fuel. Whether these are noticeable on the various models is subject to much debate.
Note: Standard UK fuel Octane rating is 95RON
Engine's that typically benefit more from higher octane fuels are ones that operate at high compression ratio's, or utilise force induction (Turbo/Super charged - although standard saxo's are not charged). Below is a compression ratio's for the various models:
1.0 – 9.4:1
1.1 – 9.7:1
1.4 – 10.2:1
1.5D – 23:1 - note that the information in this section regarding octane rating does not strictly apply to the 1.5 Diesel engine - Cetane rating take precedence
1.6 – 9.6:1 (Mk1)
1.6 – 9.6:1 (Mk2)
1.6 16v – 10.8:1
excluding the diesel engine variant, the 1.6 16v has the highest compression ratio amongst the saxo engine line. The compression ratio is approaching the limit at which standard forecourt fuel (95 RON) can be used without pinking. Consequently is most likely to respond well to the usage of Super Fuels. If driven appropriately, modest gains in MPG can be achieved too. On the other hand, the 1.6 8v engine has a relatively low compression ratio and therefore is unlikely to respond as well to the use of super fuels.
Therefore for most owners it may be more cost effective to opt for periodic fuel additive treatments. Off-the-shelf Fuel Additive Treatments are more specific in cleaning the fuel system than purely to increase the RON number compared to Super Fuels, but are a good way of carrying out a periodic cleaning of deposits within the engine and fuel delivery system. A highlight of this method is the control over the dosage (i.e when a thorough clean is needed) and timing according to amount of miles driven for instance. You DO NOT need to put additives or premium fuel into the tank each and everytime - simply adding a 'treatment/premium' tank every few weeks is sufficient to maintain good fuel system health - in doing so improving the running of your engine and keep running costs to a minimum.
The Car
Weight is the enemy for just about everything related to car performance and dynamics, and the same can be said for MPG. Increased weight means the harder the engine has to work to achieve the same results as a car weighing less, particularly during acceleration and decelerating manoeuvres, which means more fuel consumed and more expense.
Therefore, an easy way to improve your MPG is to do simple things such as removing built up junk from the back and passenger footwells, anything useless in the boot like 6x9’s and subz, and getting rid of your fat mates will all help decrease the amount of fuel your car consumes – as a general rule for every extra person in the car the fuel consumption will increase, typically in the region of 1-2 MPG.
A tyre’s job is to generate friction. However this friction affects MPG, so wherever friction can be
safely minimised, improvements in MPG can be made. Wider tyres will typically generate more friction as they tend to run softer compounds, so if you're intent of getting bigger rims, limiting the width to a sensible figure is advisable.
Choice of tyre brand will heavily affect the levels of friction and the mpg you can achieve. Track type tyres (ie soft compound such as Toyo R888's) generate relatively high levels of grip/friction and therefore should be avoided if you want to save fuel. Many manufacturers create tyres specifically designed for low friction (such as Michelin Eco's), but this will come at the slight detriment of corning and braking grip - if you're not too concerned with whether you're the fastest young'n in the land then I wouldn't worry too much about the lower levels of grip.
Cheap (un)branded tyres are a false economy in many respects, usually to increase the levels of grip to sensible and safe levels (in the dry), the manufacturers forgo heavy investment in R&D and opt to make a softer compound tyre - whilst from a safety view, in the dry this is good, tyre wear is usually high, MPG is high and in wet weather conditions can give rise to unpredictable grip levels - as a result the Cost per Mile of running a cheap tyre is likely to exceed that of running a premium branded tyre. Honestly cheap tyres are a mug game.
Regardless of tyre choice, make sure you're getting most of them by using the correct or selectively choosing your own tyre pressures, check them regularly, when do it when cold and make adjustments if necessary. Below is a list of the recommend tyre pressure for various models
165/65R14 (i.e base models and 1.4’s) – 2.2bar/32PSI – Front, 2.0bar/29PSI - Rear
185/55R14 (VTR and early VTS models) – 2.5bar/36PSI – Front, 2.2bar/32PSI – Rear
195/45R15 (VTS and common aftermarket alloy size) – 2.3bar/33PSI – Front, 2.0bar/29PSI – Rear
If you have a Sub Woofer system in the boot I suggest increasing the rear pressures by 0.1 - 0.2bar
NOTE: I've noticed several threads where people are recommending tyre pressures in the region of 30 psi all round, because 'that's what the guy at the tyre place said'. Ignore this information. It's incorrect for most road vehicles. Pressures are generally determined through the weight distribution of the vehicle. As a saxo is a front heavy car, more pressure needs to be placed in the front wheels. Less so in the back.
Weather
Cold air is favoured for the performance enthusiast but surprisingly, cold weather affects the engine in ways will usually harm MPG. The engine will remain colder for longer, so on early morning start ups the MPG can be pretty terrible. Once at operating temperature a larger proportion of the energy from the combustion will be used to maintain the engine temperature, thus less useful energy is used to move the car. So don't worry too much if your fuel consumption increases noticeably during the winter months
Humidity to certain extent is good for MPG as water vapour in the cylinder will turn to steam during combustion as well as cooling the charge, effectively retarding the ignition, causing a slight (and probably unnoticeable) increasing in power. So less throttle is needed and and consequently less fuel needs to be injected.
Improving MPG
Easy
The easiest way to improve your MPG is to adjust driving style. Accelerating hard, using the upper revs and driving above 80mph will consume a lot of fuel and make you look a tit. Instead, accelerate gently, avoid heavy braking and use the highest gear as you sensibly can at cruise. If on motorway try to stick to 70 and hold your speed. If you choose to drive at 75mph, try to stay at 75mph. Fluctuating the speed, i.e racing some other idiot on the road or overtaking another car for no reason, will harm MPG. With good anticipation skills, unless of course you hit a traffic jam, you should never need to drastically reduce or increase your speed on a motorway.
Check tyre condition and pressure
Remove any junk from the car.
Moderate
Further improvements in driving style are:
To avoid using that brake. This isn't an endorsement to just plough into cars, but rather to make use of engine braking by learning to ‘Read the Road’. This means look far ahead, predict what will happen and determine whether you’ll have to modify your speed to suit the conditions. With the extra time you've got to adjust your speed, you can make the changes much more gradually and therefore increase your changes of improving your MPG. For example there are traffic lights further up the road that have been on green for while, it makes sense that they’ll probably go red as you approach or before you have time to go past them, so sense would suggest to begin to gradually ease off the accelerator pedal and let the car slow down, the less brake the better. NOTE: this also forms part of the Advanced Driving Course.
If weather conditions are in your favour, you
can increase the pressure in the tyres by up to 0.2bar. This will 'stiffen' the tyre slightly creating a reduced contact patch and less flex in the side thus reducing friction and heat build up, thus aiding MPG, although be warned your grip will lessen.
Check and if necessary replace your engine oil with a Fully Synthetic derivative. Similarly check and replace if necessary the air filter.
MPG King
The driving style is further improved. Basically as slow acceleration and deceleration as safely possible without being a prat to other road users. When cruising on A-roads and Motorways stick to as slow as you can go (again without being a pain to others), a sensible guide figure would be around 55 mph which is a good balance between getting to a destination and achieving good mpg.
On motorways and at these suggested speeds slipstreaming can be implemented. As a car/lorry progresses along a road, it effectively pushes air out of it's way and creates a wake behind it, which if you're sufficiently close, allows your car to maintain it's speed with much less effort than previously required. NOTE this can be bloody dangerous, so concentration of the highest order is required and I'm will not accept blame should you:
a) rear end a car/lorry
b) the police kick your ass for 'dangerous driving' or similar offences
When carrying out such a driving technique, it's best to choose a lorry as their speed fluctuation is much less that a normal car and the drivers are much more used to having a row of slow moving cars pacing behind them doing the same thing as you are.
Further improvements to your 'Reading the road' technique, if you see a incline approaching, begin to gradually accelerate a few mph, then once on the incline allow the car to slow back to your cruising speed as you reach the top. When going down hill aim to maintain cruise speed rather than speed up.
Electronics – turn everything you can live without, radio, heaters, lights (if safe to do so). The alternator, which provides power to engine and it's ancillaries, runs off the engine and therefore if more power is required to supply electric to all your devices that are on, then the alternator will demand more from the engine.
Remove anything unusable/unneeded from the car, rear seats, spare tyres etc
If you're willing, have the aerial removed from the vehicle and the bodywork where it used to be flushed - the aerial is a sore point for aerodynamics so remove it if you can.
Example: One of my runs
From a 45 litre tank with what I estimate to be around 2 litres left...
That was from NA to Brighton and back again (going a slightly weird route).
I'm guessing that was around 78-80MPG. I'm afraid it's not my best run, but sadly the weather wasn't on my side. However it give you an idea of what is achievable if you're prepared to apply a few simple tips to your driving and condition of your car/engine.
Questions:
‘I’ve just changed tyres and my MPG has dropped’
See here:-
http://www.saxperience.com/forum/sho...ight=tyres+mpg
‘Will Premium fuels such as V-Power and BP ultimate aid MPG?’
In all likelihood yes, but it's marginal and ultimately depends on your engine and your driving style. As discussed above, some engines are more likely to respond better than others. In addition the cost of purchasing a premium fuel may outweigh the benefit of slightly improved mpg.
'My MPG has just (or progressively) gone crud'
First of all, a cold weather spell may have a nasty effect on MPG and is usually the biggest culprit, so always ensure whether, in particular if you're on a motorway that wind direction and speed is not to blame. Check your tyres haven't deflated excessively, check your air filter. The difference between a mucky and clean air filter can be 5-10 MPG on a saxo. Check what modifications have recently added been added to the car or engine. Has your driving style or regular drive changed?
'Does an induction kit increase MPG?'
Because highest mpg is attained when using part throttle the flow of air through the engine is relatively very low anyway... as a result an induction kit is unlikely to affect the mpg adversely at part throttle and/or light loads... Induction kits are (in theory) suppose to increase the flow of air into the engine at wide and wide open throttle. As a result the fuel has to be increased to match the air/fuel mixture. So if you boot it it'll in theory improve performance - but hurt your MPG.
So ultimately it depends how you behave.
Make sure you clean your air filter regularly too! If you've bought an induction kit they need cleaning regularly as well.
Caution with 'Open' style induction kits is needed, there is a tendency for hot air from the engine bay to be induced into the engine, the local hot air has a lower density than it's cooler equivalent outside the engine bay. This additional heat has the consequence of effectively advancing the ignition of the fuel and so reducing engine torque. So if you're at cruise you'll have to open the throttle further to maintain your speed than would otherwise be necessary, which would increase the load on the engine and likely to cause the ECU to respond by putting extra fuel (running slightly richer) and reducing fuel economy.
Below the official MPG figures for saxo models organised into three scenario's... These are good reference values for you to aim for if you're wanting to improve your mpg figures or tell if there may be a problem with your car.
Typical MPG's for Saxo Models:
1.0
Town driving - 34MPG
Mixture driving - 45.6MPG
Motorway driving - 55.4MPG
1.1
Town driving - 32.8MPG
Mixture driving - 43.5MPG
Motorway driving - 53.3MPG
1.4 (manual)
Town driving - 32.1MPG
Mixture driving - 43.5MPG
Motorway driving - 54.3MPG
1.4 (automatic)
Town driving - 26.9MPG
Mixture driving - 35.8MPG
Motorway driving - 44.1MPG
1.5D
Town driving - 40.9MPG
Mixture driving - 53.3MPG
Motorway driving - 65.7MPG
1.6 Mk1
Town driving - 28.5MPG
Mixture driving - 38.7MPG
Motorway driving - 48.7MPG
1.6 Mk2
Town driving - 32.1MPG
Mixture driving - 42.1MPG
Motorway driving - 51.4MPG
1.6 16v
Town driving - 24.8MPG
Mixture driving - 34.9MPG
Motorway driving - 44.8MPG
Hope this helps... please give feedback if you have any questions, comments or criticisms
(C) Adsayer