Miles pg/tank successes!!

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Budgetbond
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Miles pg/tank successes!!

#1 Post by Budgetbond » Wed Jul 07, 2021 6:55 pm

I seem to be just getting to the stage of getting good returns on Lpg, tho it still needs fine-tuning, so I just thought I'd open a topic for me/anyone to share there relatively good returns on Lpg to make and encourage and share tips to make it worthwhile.

I've just returned from a cheap 2 wk trip to Wales again, and I just refilled my tank with 305 miles on it assuming it would be empty despite lights still on switch to realise I still had 10 l left in the tank.

So maybe not totally accurate but 300 miles for 29l. The previous holiday empty tank was almost exactly 300 miles.

Does the quality or potency of the gas vary from station to station?

So a 600 mile holiday only cost me not much over £40 and a bit of petrol.

A couple of my previous tanks have been nearer 300 too on longer runs but not being particularly mindfully frugal.

The only thing is my normal urban driving those figures get decimated and sometimes I don't seem to get even 200 miles per tank, so I'm monitoring that at mo and looking to try and get that rectified a bit more?

Now I appreciate mine's only a 1.8vvti so it's relative, my objective has been to try and run a mildly interesting (to me) petrol ICE still sustainably and effectively for the long term, I didn't get round to converting my previous gas-guzzlers for various reasons,

so please anyone share any tips and mileage tank returns here whatever you enjoy to drive also, I'll try and keep recording my returns

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Re: Miles pg/tank successes!!

#2 Post by Avensist » Wed Jul 14, 2021 11:29 am

From my experience, the mpg figures seem to be affected by couple of factors. I always keep records on the actual miles travelled as well as the amount filled.


Temperature
Due to the nature of LPG, you get more in when the temperature is low. So, let's say you've filled it up in the early morning when it's really cold and then filled it up in the same afternoon when it's really hot, you'll get less so it appears that the mpg has improved drastically. This is especially more so if the outside temperature difference between those two fill ups are great.


Filling Stations
I find some stations get fraction more in than others though this could be due to the temperature difference mentioned above. I tend to use supermarket LPG stations most of the time.


Valve saver fluid
You say your engine is a 1.8 VVTi, which I assume it is a Toyota 1ZZ-FE engine which should have a valve saver fluid dispenser fitted. Depending on the dosage adjustment of this, I find I get more mpg.


Engine braking
My car is a Mazda 6 estate with 2.5 L5-VE engine and I do floor it whenever needed but generally use a lot of engine braking. Whenever I need to slow down, I just let the foot off the pedal and only use the brakes shortly before needing to come to standstill. Whenever I see traffic lights turn red - foot off, pedestrians - foot off, speed restriction ahead - foot off. On most modern cars, when you do this during vehicle deceleration, it cuts fuel.

With this sort of driving I get on average 31.9mpg on LPG. The other day, mixture of heavy traffic in London and some motorway driving I got 30.4mpg on LPG with aircon on. Could be due to combination of above I think and the temperature. was really hot.


Tyre air pressure
I set mine to 2.5 bar (36.2 psi) though single occupancy of the car by the manufacturer suggests 2.2 bar (31.9 psi). This seems to contribute to better mpg somehow. Mine has unnecessarily low profile 225/45R18 tyres which is the standard issue on this car. My previous car had 195/60R15 which I set that to 2.4 bar (34.8 psi) and that worked well.


Tyre choice
I am yet to replace the tyres on my current Mazda but my previous car a Toyota Avensis 2.0 with 3S-FE engine got 10% improvement by using low rolling resistance tyres. Toyo Nano Energy tyres achieved this. Same driving style as above but this low rolling resistance was noticeable straight away when these were fitted, which in turn gave even longer engine braking durations.

Tyres now have ratings on it, so go for the ones with fuel rating of 'A'. My current tyres are fuel rating of 'D' or 'E' mixture of Avon and some Chinese @!## which the car came with. I'm currently collecting data on the consumption so to see when I change my tyres to 'A' rated ones if they make any differences.

I've already got a set of Pirelli Cinturato P7 with fuel rating of 'A' last year to fit but due to lock down couldn't do much miles to get enough data out of the existing tyres. Would be interesting to see the difference if any. Was going to get the same Toyo tyres which I had on my previous cars but unfortunately they didn't do for my tyre size hence got the Pirelli this time.


Engine oil
On my previous car, when I changed the oil from 10W40 to 5W30 it has made some improvements on mpg as well as it revved more freely so switched to 5W30 despite that car had over 200,000 miles on it. Your 1ZZ-FE can run with 5W30, though it can also run with 0W20 or 5W20, which theoretically speaking should give better mpg. However I'm against those latter 2, due to LPG runs hotter and from the engine protection point, I don't go below 30 rated oil - i.e. 5W30 or 10W30 etc.

Despite the oil stays cleaner with LPG, I still change mine every 6 months or 6000 miles.

Yeah, yeah I know those from the industry will argue this point but all my engines always stayed healthy this way.


Avoid clutter
May not make much difference but I don't keep much @!## in the car. This keeps unnecessary weight off the car.


That's about it really...

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Re: Miles pg/tank successes!!

#3 Post by Budgetbond » Thu Jul 15, 2021 9:04 pm

Thanks for replying Avensist some good points there and well done over 30mpg on lpg out of a 2.5 litre is pretty good going.

You've brought up some good points there, I'm just trying to accumulate my mpg stats at the min it seems pretty good on longer runs (as expected but it wasn't always like this so I have improved it) but not so great around town still.

Good point about the variations in temperature of the fill, I usually get in about 38/39 litres into a 55l tank which is just over 20 odd quid, but I don't know whether if you reduced the P min settings in the software whether you'd get greater range out of a tank, or even if that setting s anything to do with that.

I keep meaning to run through the equivalent of the same 20 odd quid s worth of petrol for comparative mileage figures at some stage.

But yeah driving around with a full tank of petrol too would prolly add a fair bit of extra weight, I've tried to get mine pretty light as I go I've just taken my rear seats out to trace a water leak and they won't be going back in now either.

I've not actually got a valve saver fitted to mine as yet as recommended and I am mindful of it, for the moment I'm sort of trying to mitigate against it a bit, did you say you seemed to get better mpg too with a valve saver fitted to yours?

And did your previous avensis have a valve saved fitted to it or not and how did that fare at all?

And you've brought up a poignant thought I've been thinking of sometimes up and down hills I've been switching it over to petrol, and I've wondered do the Lpg ecu s also cut off the fuel supply to injectors too on coasting/deceleration in line with/ to mirror when the petrol injectors do that or not too?

Interesting about the tyres I've got the same size I up the pressure on mine fairly routinely to 40-44, I've even gone upto 50 in the past it's supposed to lower the rolling resistance by making them harder, I haven't got any comparative figures and I'm not sure whether it's great practice but I have done/do it.

And yeah bout the tyres too and your comparative figures I don't know much about tyres but I've recently gone over to all-season tyres not so good for grip in the summer but they're harder wear less/last longer at the expense of being less grippy/more slippery too to see if they're any good or not, I think there's generally a trade off of either soft grippy tyres that aren't so good for fuel economy or harder but more slippery ones that are economical and last longer but mite still be ok in weather conditions.

It did 'seem' to make quite a bit of difference mpg wise after I'd cleaned my 02 sensor s and cat out at the same time tho I didn't compile figures so I'm not quite sure, similarly when I change d my plugs and reduced the gap for Lpg bizarrely seemed also to increase the petrol mpg too, tho I can't be sure as didn't compile figures and of course like with these things it could just have been down to new plugs anyway.

I do quite often switch the engine off at lights, and I've set it to start after a dose of petrol to try n keep the engine cool, but this begs a question I don't know does the actual temperature of the Lpg gas being injected make any difference to its volatility, performance or efficiency at all?

Cheers

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Re: Miles pg/tank successes!!

#4 Post by Brian_H » Thu Jul 15, 2021 9:12 pm

If the petrol injectors are at 0, then the lpg ones will be also at 0. You can monitor that sort of stuff with the laptop, though difficult to do if your driving.

Don't run round for extended periods with very little petrol in tank while your on lpg, you risk cooking the pump if it runs dry. Thats an lpg specific hazard, as on petrol the protection for that is that the engine stops if the pump runs dry as its got no fuel left to run on. With LPG there isn't that failsafe as such. Doesn't need a full tank, but its a good idea to keep around 1/4 or higher in there (so add some more when it drops below that level)

You shouldn't need to swap fuels when driving to improve performance, if your finding its struggling under certain conditions that suggests your calibration needs some attention.

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Re: Miles pg/tank successes!!

#5 Post by Avensist » Thu Jul 15, 2021 11:50 pm

Thanks Budgetbond, this Mazda 2.5 L5-VE engine is torque based engine and pulls well and seems economical. Though it’s not one of those engines that likes high rev bands like the Honda 2.4 K24 engine.

You say the petrol comparison but measuring that in itself has its own challenges. When you fill the tank up with petrol, the gun stops automatically. From that point, depending on the car, it can take further 2 to 5 litres of fuel. You can rock the car and you’ll see the petrol goes down even if you fill it right to the cap. In my younger days, I used to work in a garage with manned petrol station so I know!

As for the valve saver, I had one fitted on my Mazda 6 right from the start as there wasn’t enough data for this particular engine as whether it needs one or not. This vehicle came out at the time when everyone went for diesels and only the minority bought the petrol versions, even then most went for the 2.0 so the 2.5 is even more scarce on the second hand market so the data on this was almost nil.

Moreover, being an engine that came out in 2008, the cost cutting strategy by manufacturers have already started and rather than taking the risk, I had one fitted at the time of conversion anyway on this particular car. The mpg seems to change according to the dosage adjustment. This I think, with certain dosage rate the engine runs leaner giving better mpg.

On the other hand, my previous Toyota Avensis didn’t have valve saver fitted. My mate still uses it, and it has over 260,000 miles and still going strong. This I knew from the start as engines of this era, like this 2.0 litre 3S-FE or 1.8 litre 7A or 1.6 litre 4A series of engines are old design engines so they are tough built than the modern VVTi variants. Furthermore, all the above series of engines, by default runs leaner on petrol under light loads.

The 7A and 4A in particular runs a lot leaner, they are one of the first engines on the market to have wide band O2 sensor (more sensitive O2 sensor than the conventional type) so they are OK without valve saver. Before the Avensis, I had Carina 1.8 7A-FE and that ran without valve saver also and was still going strong even after 160,000 miles until a @!## drove into my back and wrote it off.

As for the injectors, Brian has already summed up your question very well.

Tyre pressure wise, I think your 40-44 psi is a bit too much. Not only it’ll give reduced grip but also it will wear out the centre part of the tyre rather than evenly across the tread.

One thing I could say about the Toyo Nano Energy tyres were, the car will keep coasting a lot more. The wet grip, this one was rated ‘C’ still giving reasonable grip at normal family car type of driving. However, if you push it, the limit was noticeable immediately. So, next one up having better grip compromising a bit on economy would be Proxes CF2.

The Pirelli Cinturato P7 I bought for my current car has a wet rating of ‘B’ so I am curious to find out when I swap my current set in the coming weeks. Though, due to the wider tyres of 225/45/R18 I probably won’t notice much on the grip.

As for the life span of the tyre, the most I got out of is 70,000 miles. That was Michelin Energy 185/65R14 on my Carina. Another tips on getting the most out of the tyre is to rotate them every 6000 miles. I have always done this, so for this reason I don’t go for directional tyres (tyres that has been treaded to only go one direction).

With the front wheel drive car, two front tyres goes directly to rear wheels, whilst rear wheels are exchanged diagnoally - OSR to NSF and NSR to OSF. By doing so, you get more miles out of the tyre as they wear evenly across the 4 tyres.

As for the spark plugs you’ve mentioned, narrowing makes it easy to spark but too much narrowing will result in smaller sparks. Your 1ZZ-FE engine has individual coils per cylinder but my Avensis had coil packs each feeding 2 cylinders.

This means more wear on the plugs so I always fitted with 3 ground electrodes plugs though the standard requirement was a platinum twin ground electrodes. The gap on standard plugs were 1.1mm but I narrowed it down to 0.8mm for LPG purpose. Also I went one step cooler as well heat value 7 instead of standard 6 on NGK scale. So, I was using NGK BCPR7ET with the gap set to 0.8mm although on these you’re not meant to adjust the gap but I always done it anyway.

Done this more to protect the ignition system rather than for economy.

You’ve mentioned cleaning the O2 sensor, your engine may also benefit from cleaning the airflow meter. My Avensis didn’t have airflow meter as it was D-Jetronic i.e. had map sensor instead.

For switching off the engine at the lights, this only works if the time stuck at the lights are more than 30 seconds. When the car starts up, it eats more fuel. So with this in mind, generally if the idle lasts more than 30 seconds, best to switch off but otherwise keep it running give better economical results.

However, even for stops lasting 40 seconds, you got to balance the strain the starter motor and battery takes each time the engine restarts. You may save a bit on fuel but not greatly or you maybe forking out more on a new battery or starter motor.

Most manufacturers have introduced stop start on cars in the last 15 years or so. But if you look at the test results from various sources, the fuel saving isn’t great. So Toyota have stopped doing this stop start on newer range of cars. That itself is saying something.

The "Lpg gas being injected make any difference to its volatility, performance or efficiency at all?” Theoretically speaking yes. Reality no, or negligible differences. The more extreme example is the liquid injection type LPG systems. Vialle and alike were claiming that injecting LPG directly into the intake manifold will cool and therefore enhance efficiency performance etc. but in reality fraction if anything...

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Re: Miles pg/tank successes!!

#6 Post by Budgetbond » Sat Jul 17, 2021 2:15 pm

Hey cheers for the great info Avensist (+ Brian), yeah I prefer the more low down efficient torquey engines, that's where diesels used to be quite good, mines a slightly more higher revving engine but I've monitored my normal usage at the revs itd be beneficial to be good on Lpg and it's usually only 1-2k with motorway cruising about 3k with only the odd Italian tune up over 4k (out of approx 7k), so it sortta begs the question most engines hardly do any potential work it's no wonder they last, I know peak torque s around 4200k, I'm not sure where engines are at there optimum efficiency.

Cheers for the input I don't think you're supposed to completely fill your petrol tank riggfw to the brim are you in case of contaminating the charcoal breather tanks are you, I was thinking of running approximately the same 20 odd quid worth of petrol in mine to see how many miles i get out of that compared to a tank of lpg, I'll do it soon enough and report back the stats on here.

Good info that on the valve saver, I know mine's potentially prone, I've also wondered if anybody mixes there fluid with anything like water, methanol etc etc to cool the charge or other things.
I also wondered what the worse case scenario/contingency of vsr consequences are would it just necessitate valve clearance adjustment on engines? (Unfortunately that's sort of academic on my engine as adjustment is by reshimming and isn't that straightforward).

I keep an eye on my tyres and haven't noticed any adverse wear and still monitor them after further reading I opt for 40psi cold now, but I don't know how good/bad it is, suppose it depends on the loading/tyre type too, I know on my treads they generally say max psi 55-50.
Well thought out regarding the coasting, I'll try the rotating out.

Interesting that about the plugs funnily enough I regapped mine down to 0.8mms from 1.1 too, it's a bit easier on standard single ngk coppers tho which I kept, interesting that about going one step cooler cos I've blown a couple of coils, how does that work again then?

And interesting too about the phasing out of stop start technology is that right yeah?, I get where you are coming from, it's a bit of a compromise, I wonder whether restarting straight onto Lpg would be more efficient any idea at all?

Cheers for the good tips, and efficient heating/reducer choice of the Lpg gas is handy I just wondered whether it works better or not at any certain temperature s or not potentially?
Oh and yeah brake etc drag can be another of the main causes of mpg loss to keep an eye on I think too.

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Re: Miles pg/tank successes!!

#7 Post by Gilbertd » Sun Jul 18, 2021 1:00 am

Budgetbond wrote:
Sat Jul 17, 2021 2:15 pm
I know peak torque s around 4200k, I'm not sure where engines are at there optimum efficiency.
At the revs where they produce peak torque.....

So you aren't getting anywhere close to peak efficiency.
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Re: Miles pg/tank successes!!

#8 Post by Brian_H » Sun Jul 18, 2021 9:41 am

On the mixing front, your target usage is 1ml per litre of fuel. Can't see that working for a cooling effect, nor would you know if you'd be getting enough valve protection.

Worst case is you have valves recess enough that they don't close fully, they then burn on the seat and needs seat recutting. When I asked about it the quoted price for a replacement seat was £50 per valve required....

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Re: Miles pg/tank successes!!

#9 Post by Budgetbond » Mon Jul 19, 2021 12:25 am

Yeah peak torque rpm s max efficiency but what partic efficiency I think either side of it is a balance/compromises but actually this has given me a few further ideas, pulse and glide so the principal is accelerate quickly up to speed/slightly higher using more efficient open throttle but not quite WOT open loop up to peak torque rpm and then foot off the accelerator coasting inducing fuel cut off for as long as poss before speeding up and repeating also before approaching a hill accelerate on the level then coast/steady uphill, saving the valves a bit, then fuel cut off coasting downhill before accelerating out of the bottom to make the most of the gravity/potential energy.

Think I'll give it a try as much as poss and see if it makes any diff.

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Re: Miles pg/tank successes!!

#10 Post by Avensist » Wed Jul 21, 2021 12:24 am

Yeah, the filling the petrol up to the neck, did it back in the days when customer requested. As it was a manned station, by default wiped all the windows, emptied the ash trays, and in addition cater for any additional requests by the customers, like tyre pressure check etc.

As for the VSR, Brian has already covered potential outcome of it.

You seem to be more concerned about the cooling, this is where my heat value of the spark plugs comes into. Cooler the plug, it can suck more heat out from the combustion chamber. The use of LPG, the combustion chamber temperature will be higher than running on petrol.
For this reason, I use a step cooler plugs with the vehicle with LPG. The downside of this is, if the vehicle is used on petrol short journeys a lot, the plugs may not achieve the self-cleaning capability and may cause ignition issues in the long run. Nonetheless, not an issue if frequently run on LPG.

As for narrowing the gap for the spark plugs, I do this to protect the ignition coils. This is not to be confused with running on cooler plugs, these are two separate things.

Narrower the gap between the centre electrode and the ground, much easier for the sparks to occur. Wider the gap, it requires more voltage to create the sparks, if you like, think it as it tries to suck more power out of the coil, putting more strain on the coil.

The required voltage depends on various factors but one of it is how easy the given fuel state is as well as air and fuel ratio. Generally, LPG is more difficult to ignite than petrol thus requires more voltage which strains the coil. So, I personally narrow the gaps to reduce the strain on the coils.

Like I said on my previous Avensis, the plugs were easy to get to and was using standard plugs, however on my current Mazda L5-VE engine, each cylinder is fitted with the coil so it is hassle some to check frequently and for this reason, the manufacturer specifies Iridium plugs.

The standard requirement for this engine calls for NGK plug LTR5ARX-13P. This means, the heat value 5 with gap of 1.3mm.
I have replaced this with the same NGK plug but with PLTR6A-10G, which has the heat value of 6 and the gap of 1.0mm.

Whilst we are on the subject of cooling, most modern cars have coil per each cylinder which sits on top of the spark plugs directly, unlike the previous designs where coils were remotely mounted and fed the sparks via HT leads.

The modern design of engines having coil per each cylinder has illuminated issues that HT leads introduced, however in turn due to the nature of sitting on top of the one of the hottest part of the engine, the coil's life span is somewhat shorter compared to the conventional designs. Moreover this problem I feel has accelerated further by cost cutting done across the manufacturers.

One of the biggest factors that shortens the life the coil is the heat. For this reason, on my car I have removed the engine cosmetic cover to cool the coils. Most modern engines have this cosmetic cover, usually with engine names or series written on it and their function is to make it look neat and some may have slight sound proofing functions but that's about it. It traps heat and strain the coils and wirings. So I have removed it.

As for starting up on LPG, I did so on my Avensis because one time I was doing a lot of short journeys. Don't know about the efficiency but certainly prevented oil contamination as well as easy on the wallet.

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Re: Miles pg/tank successes!!

#11 Post by LPGC » Wed Jul 21, 2021 8:19 pm

Depends what aspect of efficiency we're talking about. The engine is most volumetrically efficient at the rpm that the torque peak occurs but that doesn't mean it is the most fuel efficient, thermally or 'other losses (friction etc) efficient at that same rpm.... Usually an engine will be more fuel efficient at lower than peak torque rpm, unless it is underpowered for the vehicle.
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Re: Miles pg/tank successes!!

#12 Post by Budgetbond » Thu Jul 22, 2021 2:48 pm

Cheers for all those tips Avensist, and thanks for explaining that Simon, I've just got to refill again got 240 miles outta the tank normal round town driving so I think it needs a bit of work on the important lower revs ranges.

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Re: Miles pg/tank successes!!

#13 Post by Gilbertd » Thu Jul 22, 2021 6:03 pm

Budgetbond wrote:
Mon Jul 19, 2021 12:25 am
Yeah peak torque rpm s max efficiency but what partic efficiency I think either side of it is a balance/compromises but actually this has given me a few further ideas, pulse and glide so the principal is accelerate quickly up to speed/slightly higher using more efficient open throttle but not quite WOT open loop up to peak torque rpm and then foot off the accelerator coasting inducing fuel cut off for as long as poss before speeding up and repeating
and really piss off anyone following you......
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Re: Miles pg/tank successes!!

#14 Post by Budgetbond » Thu Jul 22, 2021 7:51 pm

Lol thought you mite chip in with that idea Richard!!, well you don't have to do a full on version but it's good just to know that when you step off or reduce the gas that the injectors 'll stop if you release the pedal completely.
But in retort to your response I've since read that sometimes they have actual corporate convoys all doing it together in unison tailgating!!!

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Re: Miles pg/tank successes!!

#15 Post by LPGC » Fri Jul 23, 2021 1:25 pm

You're more likely to use more fuel doing pulse and glide and probably more chance of you or someone else having an accident.
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Re: Miles pg/tank successes!!

#16 Post by Brian_H » Fri Jul 23, 2021 8:34 pm

LPGC wrote:
Fri Jul 23, 2021 1:25 pm
You're more likely to use more fuel doing pulse and glide and probably more chance of you or someone else having an accident.
I've found the best economy can be got if your able to use cruise control, which sort of makes sense when you think about it. Definitely agree with the the above, and as Richard pointed out likly to really annoy the hell out of anyone following you (which they might do more about than flashing lights or hooting at you!).

I can generally get around the 30mpg mark indicated on petrol on the motorway (sadly without cruise control as its broken and haven't managed to get round to fixing it) out of a 2.3 people carrier. Which I have had get as bad as indicating an average of below 7mpg around town (combination of a cold start and very slow traffic in Bath was the worst occasion for this - 6.3 was the lowest it managed to get). Roads with less smooth conditions (dual carriageways or slower roads where your stuck following slower traffic) make a noticable drop to the figure.

Even fairly busy motorways (the M1 being the prime example) tend not to stray too far below 27mpg even with fairly heavy traffic.

The convoy stuff I think is probabbly slightly out of context - and a lot of that is to do with reducing drag with larger vehicles to improve overall economy (the front vehicle wouldn't notice a benefit, but the ones following would). Doesn't really apply to a car.

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Re: Miles pg/tank successes!!

#17 Post by Gilbertd » Fri Jul 23, 2021 10:13 pm

I'd query that cruise can save fuel. I once took a borrowed Chrysler Grand Voyager to Switzerland. It had a trip computer that could display instantaneous fuel consumption. With cruise on going uphill I once saw it showing as low as 4mpg. I tend to hold the throttle steady so lose a bit of speed when going uphill but can then back off the throttle to maintain speed when going down the other side. Well, I do if I'm getting low on gas and want to save a bit to avoid having to run on petrol, normally I just give it some welly going uphill to maintain speed. I don't really see the point of trying to get the last mile out of every litre, just enjoy the drive, You're running on half price fuel, even if you drove it like you'd stolen it, you'd still be saving money so what's the point?
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Re: Miles pg/tank successes!!

#18 Post by Avensist » Fri Jul 23, 2021 11:09 pm

I quite agree with Gilbertd. Some cruise control tries real hard to maintain speed and that dents the mpg figures. Also, even when resuming back to the previously set speed following a slow down or braking, if that 'Resume' button is pressed, it feels that it's trying to get back to the speed really quickly and I can assume it's relatively a sharp acceleration.

For this reason, I only tend to use cruise control when it's relatively flat road or in that annoying road works with average speed cameras. Any other times, I do exactly what Gilbertd does - hold the throttle steady even losing a bit of speed uphill.

And also I do floor it every now and then, just for fun as well as clear the gunk.

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Re: Miles pg/tank successes!!

#19 Post by Brian_H » Fri Jul 23, 2021 11:32 pm

Maybe I was just lucky then! That was what was noticed on the Disco 2 when I drove it upto Liverpool, though it probabbly helped more that the traffic was fairly light. MPG figure in that case was calculated by filling on departure and resetting trip, then refilling and using the fill figure and miles recorded on the trip as the D2 doesn't have the mpg readout.

Worthwhile flooring it as you say every so often as well!

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Re: Miles pg/tank successes!!

#20 Post by LPGC » Fri Jul 23, 2021 11:56 pm

A driver can always beat cruise control at fuel economy. A driver can anticipate situations such as uphill / downhill stretches and balance throttle with maintaining current speed and with the economy savings of speed decreases on uphill stretches and speed increases on downhill stretches - Cruise cannot do that.

Imagine yourself having to push a trolley up and down little slopes (say in a warehouse or skateboard track), you'd anticipate slowing down slightly pushing uphill so would make sure you'd get a run up to avoid having to work flat out pushing uphill and you'd expect to speed up going downhill so would anticipate slowing down just before you started on the downhill stretch. An engine won't get tired like you do but still has to put in the forces you do and use up energy like you do.

Gravity is effectively an accelerative force (decelerative uphill) and you will always use more fuel when accelerating (or maintaining same speed against a decelerative force). If you use momentum to help go uphill while decelerating slowly you are effectively not accelerating while maintaining constant speed. But you have to strike the right balance because if you allow too much actual deceleration going uphill you will have to accelerate again to regain the original road speed even if that is on the flat.

A helicopter hovering at steady altitude would accelerate upward at roughly 30mph per second (0>60mph in 2 seconds) if it were not for gravity applying the opposite same force. Drive up a 1:3 hill in a car and the decelerative force is around 10mph per second. It would take more overall fuel to maintain constant speed in a car to maintain same speed up that hill than to accelerate more slowly on run up to the hill and slow down during going up the hill than to maintain same speed throughout the run up and going up that hill as long as the overall average speed were lower during the run up and the hill. But then there's the downhill stretch and you can use very little power to go downhill.

But cruise control will likely save fuel over a driver who slows down too much on downhills and speeds up on uphills, or one that changes speed willy nilly and doesn't anticipate uphill/downhill.
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