tjolliffe Posted May 3, 2010 Share Posted May 3, 2010 I'm sure this has been asked before but....what MPG are you getting? I've got a 3.9 RRC on LPG and i've worked out that i'm getting just under 10mpg on gas - doesnt seem that great (yes I know its a V8 but even so...), especially annoying because it means the gas tanks are never big enough! Any imput would be great, just want to see if what i'm getting is normal/abnormal? Quote Link to comment Share on other sites More sharing options...
DC_ Posted May 3, 2010 Share Posted May 3, 2010 About normal I would say. My mate also has a 3.9 disco and that also worked out at about 10mpg Quote Link to comment Share on other sites More sharing options...
elbekko Posted May 3, 2010 Share Posted May 3, 2010 Sounds about right for a 3.9. Quote Link to comment Share on other sites More sharing options...
teslo Posted May 3, 2010 Share Posted May 3, 2010 10mpg on LPG is about right...but also depends on driving style, LPG system( closed loop...) Quote Link to comment Share on other sites More sharing options...
Highway_Star Posted May 3, 2010 Share Posted May 3, 2010 Under 10 on gas is about right? What are you guys smoking?! On the motorway mine returns 20-22mpg on petrol, 18-20mpg on LPG. Round town, of course it's a different story, 16-18 on petrol, 12.?-15 on LPG. Never got over 15 in town on gas for some reason. That's 3.9 hotwire EFi, OMVL Millenium closed loop system. Engine is pretty standard, other than the camshaft, which is nothing wild, just puts the power band in a better palce for the autobox really. I have the ignition timing set at a compromise where it runs OK on both fuels, erring if anything on the LPG side. Probably in the 12-16 BTDC range. Quote Link to comment Share on other sites More sharing options...
rocksteady Posted May 3, 2010 Share Posted May 3, 2010 I'm getting about 12 general running around. About 15 on a run. The car is a 93 lse 4.2, with 35in tyres, so not bad. Thats on lpg. Quote Link to comment Share on other sites More sharing options...
teslo Posted May 3, 2010 Share Posted May 3, 2010 hm, i am not used to MPG values...so maybe i am wrong with conversion...anyway my 3.9 was doing around 25-28L/100km in town. It is BRC without ECU. Quote Link to comment Share on other sites More sharing options...
DC_ Posted May 3, 2010 Share Posted May 3, 2010 I've got some heavy stuff on mine so it doesn't get the best MPG mind. Would be better on road tyres etc Quote Link to comment Share on other sites More sharing options...
g&t Posted May 4, 2010 Share Posted May 4, 2010 Had a 3.9 auto back in '02, LPG 14mpg (3.08miles/litre) on standard 205 road tyres, seemingly regardless of (on-road) useage. I don't drive any vehicle hard either. Quote Link to comment Share on other sites More sharing options...
chopes Posted May 5, 2010 Share Posted May 5, 2010 My 3.9 EFI Vogue has been on LPG since 2003 14 mpg in my experience is the average that I get and most other people. The other point to consider is that LPG is only 70% efficient compared to petrol. Quote Link to comment Share on other sites More sharing options...
plasticbadger Posted May 5, 2010 Share Posted May 5, 2010 Under 10 on gas is about right? What are you guys smoking?! On the motorway mine returns 20-22mpg on petrol, 18-20mpg on LPG. Round town, of course it's a different story, 16-18 on petrol, 12.?-15 on LPG. Never got over 15 in town on gas for some reason. That's 3.9 hotwire EFi, OMVL Millenium closed loop system. Engine is pretty standard, other than the camshaft, which is nothing wild, just puts the power band in a better palce for the autobox really. I have the ignition timing set at a compromise where it runs OK on both fuels, erring if anything on the LPG side. Probably in the 12-16 BTDC range. I agree, I only ran mine standard for about 4 weeks, but averaged 18-20mpg on petrol on a mix of town / open road. I never got round to fitting the LPG kit so can't comment there. I'd say look at how your engine runs, ignition, mixtures airfilter etc. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 5, 2010 Share Posted May 5, 2010 I'd be looking at what is killing the MPG too, things like tyres, roof racks, roll cages, bootful of carp etc is all going to really kill it. Then there is the maintenance aspect: dizzy, timing, coil, ignition amp, leads, plugs, air filter, sticking calipers Then if its higher mileage: Camshaft, head gasket failure (common into valley), worn cylinder walls. If it is a standard vehicle on stock tyres and not on inter-galactic mileage then yes, 13-15mpg is about right.... on gas mixer system, a little more on a sequential. Quote Link to comment Share on other sites More sharing options...
tjolliffe Posted May 5, 2010 Author Share Posted May 5, 2010 Thanks for the response guys. It's a totally standard rangey, 150k on the clock so wouldnt say its done LOADS of miles. Engine seems sweet no odd noises doesnt get hot ect. It's open loop LPG so I know that doesnt help the MPG. I've had a mess about with the mixture screw and managed to make it run quite a bit leaner and also advanced the timing so hopefully that'll help the MPG. Guess i'll find out on the next fill up! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 5, 2010 Share Posted May 5, 2010 Making it leaner won't save fuel, just mean you are down on power and you have to put your foot down more to compensate = less efficient. 150K *is* a lot on a V8, they hide wear/noises well, but if it hasn't had a cam, then it is about twice overdue it! This is most likely your problem in all honesty. Quote Link to comment Share on other sites More sharing options...
sean f Posted May 6, 2010 Share Posted May 6, 2010 I got 14.5mpg according to the onboard electronics. Thats was a run from Newton Aboot in Devon up to West Harptree and back, not being driven gently. It was about what I expected for a 4.6 P38 with 230000 miles on the clock and BFG mud terrains fitted. I get about the same round town normally. Managed to get up to 24mpg once but that was following a 110 towing a trailer with a 90 on it so driving extremely gently ( and boy was it boring!). Quote Link to comment Share on other sites More sharing options...
tjolliffe Posted May 6, 2010 Author Share Posted May 6, 2010 Making it leaner won't save fuel, just mean you are down on power and you have to put your foot down more to compensate = less efficient. 150K *is* a lot on a V8, they hide wear/noises well, but if it hasn't had a cam, then it is about twice overdue it! This is most likely your problem in all honesty. Surely if it was running too rich before then it was not burning all the fuel given to it hence - uneconomical. Wouldnt Making it run leaner compensate for this thus making it more efficient? I'm limited in my knowlage of V8's i'll admit but I thought that was the basic rule of thumb.... I've not noticed any real drop in power either. As for the engine mileage, again, I dont know too much about V8's, only ever owned Tdi's but perhaps 150k on the clock is alot, i'm not too fussed though as the truck cost me next to nothing to buy so i'm happy to run it into the ground! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 6, 2010 Share Posted May 6, 2010 Yeah, *IF* it was too rich before, maybe, but you have any proof of that? Chuck your local garage(hopefully one with LPG knowledge) a fiver and get them to set it up on a gas analyser at idle and 3000rpm, that's all you can really do with closed loop systems Quote Link to comment Share on other sites More sharing options...
jules Posted May 6, 2010 Share Posted May 6, 2010 I have just bought a P38 4lt 2001 with around 100k on the clock the shocking thing is the trip was recording 18.3mpg over the last 3000 miles which I was well happy with then this morning I must hve reset it which noticing or it automaticly does at 3000 miles thismorning it was averaging 21.5mpg which for my driving is a shock I assume it will droop back down to 18 again. the thing is I was assuming that it was so high because it had not adjusted to my flat out driving style and that in reality it was doing around 13mpg like my old one used to do so I didn't want to rest the trip meeter fearing the mpg would not be as good.(if any of that makes sence) It goes for an LPG kit to be fitted at the end of the month as its my new daily driver from Southampton to Bournemouth everyday Quote Link to comment Share on other sites More sharing options...
MartinM Posted May 9, 2010 Share Posted May 9, 2010 I have just bought a P38 4lt 2001 with around 100k on the clock the shocking thing is the trip was recording 18.3mpg over the last 3000 miles which I was well happy with then this morning I must hve reset it which noticing or it automaticly does at 3000 miles thismorning it was averaging 21.5mpg which for my driving is a shock I assume it will droop back down to 18 again. the thing is I was assuming that it was so high because it had not adjusted to my flat out driving style and that in reality it was doing around 13mpg like my old one used to do so I didn't want to rest the trip meeter fearing the mpg would not be as good.(if any of that makes sence) It goes for an LPG kit to be fitted at the end of the month as its my new daily driver from Southampton to Bournemouth everyday My 2000 P38 4.6 with about 99k on the clock varies depending on what sort of journey I'm doing. Certainly I can see (from a reset) up to 26 miles per gallon if I'm simply doing clear motorway work and on a reasonable 28 mile commute (combined local and motorway work) I tend to average out at about 19.5 over a period of a week doing nothing aside from the commute. I did fit an ITG Maxgen Airfilter in place of the original and this seemed to improve consumption by up to 10%. Round town it tends to be closer to 15mpg - and towing the horse trailer (laden) means the average falls to 10 to 14 (again depending on whether this is short or more sustained distance work) which I'm still quite happy with (or at least was before petrol went over the 120p per litre price.) I still tend to think the V8 burns fuel as a function of time rather than anything else (though maybe this isn't the case if you travel at 70mph rather than 65!) I have been reluctant to go to gas because of the up front cost, but I'm beginning to think again about this - however if it means falling from say 19 to 10 MPG for the commute then the benefit is maybe not so good. I'd be interested to know what you get after you gas yours! Keep us updated. Thanks Martin Quote Link to comment Share on other sites More sharing options...
g&t Posted May 11, 2010 Share Posted May 11, 2010 I've had a mess about with the mixture screw and managed to make it run quite a bit leaner and also advanced the timing so hopefully that'll help the MPG. Guess i'll find out on the next fill up! The outfit that fitted my LPG (never again!) system warned against 'leaning' the mixture as the combustion chamber temp. with this stuff is high enough as it is. I'm going to upset some people now I know, but why are so many RR V8 owners so obsessed with mileage returns? You know that a 2 tonne, perm 4X4 with a V8 & auto-box is going to drink (lets not pretend that LPG conversions are carried out for the sake of the enviroment) so if you can't afford to run it, stick to a hatchback. If some owners sat down & worked out the true long term costs of their conversions they would discover that 'half-price' motoring promises are in fact a myth. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 11, 2010 Share Posted May 11, 2010 Long term.... I paid £200 for my LPG system on my Range, fitted it myself, swapped it between my old range and new one, did about 15,000 miles on it. Petrol, 14-15mpg, gas was 12-13, at the prices when I was running LPG it was 50% (or less at times) of the cost of petrol, so it was the difference between getting 14mpg, or the equivalent of 24-26mpg, based on cost per mile. That was with mud tyres etc though ^^ So not quite half price, but damned close to it(!), and frankly anything that allows a V8 rumble on a budget is fantastic Quote Link to comment Share on other sites More sharing options...
Off Road Toad Posted May 11, 2010 Share Posted May 11, 2010 Miles per gallon this sounds like a diseasal owners conversation In all seriousness though, i'm getting about 9.5 mpg from my 4.6 90" with 35" tyres. Thats when i enjoy it If i'm boring and hold the traffic up and drive it like a diesel series towing 4 tons then i get 15- 18mpg out of it. I just accept it uses fuel like no tomorrow and fill it up when it's empty (kin expensive at the moment tho ) Steve Quote Link to comment Share on other sites More sharing options...
g&t Posted May 12, 2010 Share Posted May 12, 2010 Miles per gallon this sounds like a diseasal owners conversation Steve For my part Steve wash your mouth out with soap & water (or unleaded) (3.5 efi for the record ) Quote Link to comment Share on other sites More sharing options...
mickeyw Posted May 12, 2010 Share Posted May 12, 2010 WTF!!! How does anyone get more than 15MPG from a V8 of any capacity?? Do you all drive like nuns ?? My 3.9 Ninety auto with 255/85 MTs does about 10-11 MPG (on gas) on general run around work, the same gas MPG as my RRC with same power/drive train but standard road tyres. The Rangey can manage 14-ish on a run if I stick below 70MPH. Quote Link to comment Share on other sites More sharing options...
g&t Posted May 13, 2010 Share Posted May 13, 2010 WTF!!! How does anyone get more than 15MPG from a V8 of any capacity?? Do you all drive like nuns ?? My 3.9 Ninety auto with 255/85 MTs does about 10-11 MPG (on gas) on general run around work, the same gas MPG as my RRC with same power/drive train but standard road tyres. The Rangey can manage 14-ish on a run if I stick below 70MPH. My 3.9 auto used to return about the same on a long run with 20-21 on petrol & this with a mixture of 70-75mph on m/ways & 50-60 on A roads. I don't 'drive like a nun' but neither do I drive like a certain TV presenter! Quote Link to comment Share on other sites More sharing options...
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