How to improve fuel efficiency of a car…

Bought myself an old Saab 9-5 diesel 3l tid for cheap…fuel economy is a bit poor so wondering if there is any way to improve this.

I’m thinking keep on top of tyre pressures, air filter and fuel filter change..its already had an oil and filter change.

Anything else I should be doing and is the above easy enough to do at home for a mechanical simpleton?

Want to avoid a full service, cost is around 240 quid for the model of car…

Anything else I should be doing

Ride your bike more?

Change fuel filter if not been done already

Drive it less.

Block shifting (1st to 2nd etc…can be weird at first but once you learn to let the revs drop it’s smooth, as long as the ratios aren’t too far apart)

Play the no braking game, if you have an average mpg display it makes a noticeable difference, all that time off the gas is free mileage so the more roundabouts, the bigger the savings.

Drive as if you are going to run out of fuel 5 miles from your destination…tickle that accelerator!

Don’t leave your car warming up each morning, break out the scraper and get driving.

Drive slowly. I’m not being facetious here, simplistically kinetic energy = mass x velocity^2 so that’s where most benefit lies.

Run a few bottles of injector cleaner stuff through the next tanks of fuel. Might not make a huge difference, but won’t do any harm.

Don’t brim the tank n empty all the shite out of it.

The pedal on the right ….. don’t push it so hard. Also, as already said, lift off earlier than normal before braking, you’ll be amazed at how much fuel you save – and you can pretend you’re driving a F1 car!

If you don’t have a display showing your fuel consumption it can be a bit tough to know if you’re actually achieving anything though.

Its a 3 litre…..what were you expecting fuel economy wise from it ?

Also tickling the throttle and accelerating slowely is rarely the most economical way to drive, as well as being a sure fire way to piss off other road users.

Dont drive it round town , use it on long motorway journeys at quiet times traveling at 60mph. That will be your most economic.

Smoother driving.. be way more pre-emtive with braking and no fast accelerating. Go 10% slower.

it’s not rocket science, is it, my first car was a Citroen GSA, it had some elementary light display on ‘fuel economy’ — suspect it was just throttle pressure or some such. But now that correct car has instant MPG, same is much the same – get up to travel sped firmly, then look ahead and don’t try gunning it for the next gap..

roof bars – take them off if not in use.

fill tank to 3/4 rather than full. make sure fuel has been flushed – so either brim to empty all the time, or does to 1/5 and then refill – my old Saab got knackered as I tried to avoid the expensive fuel stations and clogged the tank/outlet with gunk instead..

Make sure it’s had a stage 0 mod – basically do all the service items. Make sure tyres are in good nick, inflated ok, suspension all works as it should. Engine – oil and filter, plugs, HT leads, air and petrol filters. Check the forums to see if anything else is a common problem in your particular car that might make it run roughly/badly. Change coolant for fresh stuff. Check for oil or fluid leaks, if it’s an auto change the box fluid if needed. Make sure all the lines and hoses are in good nick. Check for signs of HG failure. Compression test to make sure that’s ok. Check injectors are running ok. Make sure battery is in good health.

All the above you can do yourself. Then go and get a remap with someone who does it PROPERLY. NOT just a one size fits all but a custom map that takes into account the age and spec of the car. This will make it use fuel more efficiently if you don’t use the extra power they often bring when done. I can recommend someone in West Yorks if you are round here.

And last of all enjoy it! It’s a fun car, don’t worry too much about MPG. Drive carefully when you just want to get somewhere, floor it when you want some fun.

EDIT my new car does 16mpg around town but it’s awesome! RWD and petrol -heaven!

Also tickling the throttle and accelerating slowely is rarely the most economical way to drive, as well as being a sure fire way to piss off other road users.

I didn’t mean accelerate slowly, but not to do the point and squirt method of driving. Or changing lanes and giving the gas a big prod to boot it from 50 to 70mph.

Also made a typo with block shifting. I mean 1st to 3rd, for example.

HT leads

Good luck finding those on a diesel robdob.

Drafting the car in front seems to be popular round these parts

Reduce the weight it’s lugging around. Don’t carry a load of crap in the boot, only half fill the tank….

simplistically kinetic energy = mass x velocity^2

And meaninglessly 🙂

Most of the energy used up when driving is to overcome wind resistance. So slowing down even a bit (or just sticking to the speed limit!) saves quite a bit.

Also:

– consistent speed – use cruise control on open not too hilly roads – constant speeding up and slowing down costs energy
– lift off well before junctions, sometimes pressing the throttle just lightly as you still slow down will let you almost coast for ages. Not good when it’s busy though
– when it’s time to change tyres, get energy saving ones – they are decent nowadays, don’t cost more, last twice as long and save a bit of fuel

The first three points make by far the most difference in any car.

my new car does 16mpg around town but it’s awesome!

Don’t take fuel economy tips from robdob 😉

Shifting 1st to 3rd is no good. You’re driving the car in a less economical way in 1st gear before you get in to 3rd. You’re far better off changing gear more frequently and keeping the engine within it’s most efficient rev range as long as possible even if you’re only in 2nd for a few seconds. You want to be in the right gear at all times.

Basically its acceleration that kills fuel economy. So don’t carry any unnecessary weight around don’t follow cars too closely so you can better manage the throttle and minimise braking (braking is more often than not followed by acceleration).

Very little you can do when driving in and around a busy town or city, best results are on the open roads obviously. Also avoid minor roads in favour of dual carriageways even if the route is a bit longer, but avoiding junctions, traffic, bendy roads requiring speed changes.

Goes without saying make sure the car is well maintained with decent tyres properly inflated and in my diesel SMax I do see a noticeable difference by using the higher grade fuel (VPower or equivalent).

simplistically kinetic energy = mass x velocity^2
And meaninglessly

This might be more or less meaningless but DRAG is also proportional to V^2 so it really is rather simple. Only filling the tank 3/4 full and duct taping the panel gaps etc are wholly secondary effects and the most effective way to save fuel is to slow down.

The force required to defeat wind resistance increases by 36% traveling at 70 mph compared to 60 mph and Power = FxV so you need 59% more power at 70 mph compared to 60 mph and that = fuel. So even with nothing else changing (drivetrain losses etc) this is the ‘big win’.

Basically its acceleration that kills fuel economy.

No, it’s mostly speed and using power where you don’t need it – ie driving up close to junctions then braking, when you could’ve been decelerating gently.

On cars with an instant economy reading, all you have to do is lift off imperceptably, so the speed falls by 1mph every few hundred meters, and the FE reading goes through the roof. Likewise ease down a similar tiny amount and it drops right down.

And what jemima says. Doing my regular M4 run at a constant 70mph in the Passat I can get 62mpg, at 80 I’d get 54mpg.

Possibly a bit of a thread hijack, but has anyone any experience of these engine decarbonising jobs? Basically some sort of gas in the engine to clean out carbon deposits and buildups.
Was thinking of having it done, but snake oil??

Do this to it

Hah. Just bought two different snake oils from Halfords – EGR cleaner and combustion de-coker, as I was getting a few puffs of black smoke. The EGR cleaner you’re supposed to spray into the air intake in 1 second bursts. Sprayed a tiny burst in and the engine coughed, shuddered, blew a cloud of thick black smoke *back out* of the air intake and stalled.

Despite my misgivings it restarted fine and completed the rest of its treatement as described – it’s a bit smoother tbh. Haven’t tried the de-coker yet. Smoke wasn’t there yesterday when my Mrs was revving the hot engine in Waitrose car park, so maybe it’s improved.

How many miles a week do you drive.

Unless you are driving hundreds of miles a day (week) then fuel economy differences save you surprisingly little money (as fuel economy is a reciprocal, once you are getting over about 40mpg, the savings start getting vanishingly small….)

ie 100miles:

at 25mpg is 4 gallons (~£18)
at 50mpg is 2 gallons (~£9 saved)
at 100mpg is 1 gallon (~£4.5 saved

In reality, unless you are hypermiling, which in todays traffic is a massive PITA to both you and other drivers, you can probably increase your mpg by maybe 10mpg tops.

FFS, Just boot it and enjoy! Why drive like an old Grandad for the sake of a couple of quid a tank!

Yes. We’re told how inefficient it is if you only ever drive to the shops and back. Which it is, in MPG terms, but a tank still lasts bloody ages if you travel 20 miles a week.

you can probably increase your mpg by maybe 10mpg tops

That seems reasonable. I’ve driven the M4 between Cardiff and Reading hundreds of times since I got the Passat – first time out I got 48mpg, then it kept going up and up to 55mpg, then I got eco tyres, and my (repeatable) best is about 62mpg. No idea why it went up gradually like that.

FFS, Just boot it and enjoy! Why drive like an old Grandad for the sake of a couple of quid a tank!

Other points of view are avaiable!

Big article in Car Mechanics magazine this month on this(decarbonizing treatment)including Terraclean, and also using crushed Walnuts.
Might be worth a read if your interested.

Money saved in fuel by using eco tyres for me would be wasted when i would be using winters or all seasons from oct to may…..i believe the op is in edinburgh and so would benifit from having tyres suitable for cold weather.

@unovolo is that available online? Bit of a problem getting specialist magazines (snigger) over here!

Knock it out of gear down hills or as much as possible. Can’t do that with an auto of course but thats why i’ve always bought manuals.

Related to this, there’s a long hill with a nice long flat run out near where i grew up and take the “how far can i travel out of gear until i get under 20 mph” game. Done best in my c class estate but my old man still wins by passing the pub back in the 80s with his Volvo 260 lump, not sure i’ll ever beat it but i’ll keep trying. 😀

Knock it out of gear down hills or as much as possible.

We’ve done this before. Does not help, necessarily.

Money saved in fuel by using eco tyres for me would be wasted when i would be using winters or all seasons from oct to may

Why? They still last longer and use less fuel in the summer…? They aren’t significantly more expensive than anything else decent either, at least not for my car.

santacoops, I think if you coast downhill in gear, the engine is running without fuel until the revs drop to a certain value – if you press the clutch, the engine needs fuel to idle.
Not sure your advice is correct……but of course, I could be wrong!?

Not sure either mate. I know my mpg count goes up when i knock it out of gear though. Happy to be corrected of course. I think i just wanted an excuse to mention my coasting down a hill game. 🙂

I think you need to coast in gear. That way the wheels drive the engine and uses no fuel. If you press clutch or take out of gear the engine needs to burn fuel to idle

Id have to buy new wheels and tyres , thats alot of fuel to pay for tyres and wheels ……and storing them etc etc .

Im only gonna have 1 set of tyres and they will be the ones that benifit most of the year rather than 4 extra mpg 4 months of the year.

Id have to buy new wheels and tyres

Ok, so your specific situation is special, congratulations on your special snowflake award 🙄

For most of the rest of us though, the point stands. And anyway, winter tyres are also available in eco flavour. Nokians all use the low RR compounds.

Trekex I think you are right.

If my understanding is correct, modern engines can shut the fuel off when coasting in gear because the car’s weight keeps the engine rotating not the combustion cycle.

Also coasting out of gear in a manual is not IMO very safe. If you need to access some pull you’ve got to get it back in gear. 1-2 seconds (if you are quick and don’t miss the gear), enough time to contribute to an accident. Not an issue in an auto as the pick up is quicker and automated, squeeze and go.

And for the OP.

Moderate throttle inputs help but nothing has an effect on economy like planning and anticipating, leaving healthily large gaps and keeping the speed down to road legal levels.

Eco tyres might get you a few % but I’ve never used them.

I have had the same car a long time and I’ve been through periods where the indicated average was barely 41-42 compared to the current 47-48 with the same commute and similar use throughout. Getting better at planning and anticipation is a big part of that variation as is learning the car’s sweet spots for acceleration, gear selection and ability to carry and use its momentum.

Eco tyres might get you a few % but I’ve never used them.

Bout 5%, best case, sometimes 3-4% – for little extra expense unless you are currently using cheapo tyres. But as said they last at least twice as long which has a bigger effect on your pocket.

Progressive driving is the single biggest thing you can learn.

That said a 3.0l.. It’s never going to be great..
I had a 2.4t v70.. Fun driving returned about 19mpg.. Driving incredibly smooth and progressive bumped it up to about 25-27. That’s mixed mostly urban, maybe 20% motorway.