Old thread resurrected!
Interesting how economy calculations done today would compare to when the thread started in 2012...
As jsut said, diesels are much more frugal than petrols, accepting they are slower and noisier (at least the ones suitable for veg oil without any changes are)
Let's take my T25.
Diesel - 100miles @ email@example.com/l = £18.41
Veg Oil 100miles @ 35mpg@£1.00p/l = £12.97
Petrol - 100 miles @ 20mpg@£1.38p/l = £31.32
LPG - 100 miles @17mpg @ £0.69 = £18.42
As you can see, just being a diesel makes it cost the same to run as LPG, the benefit of vege oil just adds. You can get oil anywhere, but even if you can't, diesel is fine.
I would never swap my T25 for a petrol even if it was on LPG. I filled the tank and took 20litres of oil in the back and got 700miles without a fillup.
December 2015 and that would look like:
Diesel - 100miles @ firstname.lastname@example.org/l = £13.41
Veg Oil 100miles @ 35mpg@£1.00p/l = £13.02
Petrol - 100 miles @ 20mpg@£1.04p/l = £23.71
LPG - 100 miles @17mpg @ £0.50 = £13.41
But the above is for a VW T25, where according to provided figures the diesel version will do over twice as many mpg as a petrol version running on LPG. For most other vehicles, the diesel version won't do nearly twice as many mpg as the petrol version, even than the petrol version running on LPG... In the real world, for most models of vehicle, the petrol version converted to LPG will be cheaper to run than the diesel version simply in terms of fuel. i.e. before we even get into the far greater likelihood of the diesel version needing expensive parts changing such as DMF's, DPF's, EGR valves, injectors, gearbox (due to power delivery at low rpm so gearbox sees more torque more often). Most of those parts don't come cheap but are either not fitted at all on petrol engines (DPFs and direct diesel injectors, in some cases DMF's) or don't break even a third as often on petrol vehicles as they do on diesel vehicles. Back in the day when petrol cars had points and carbs and diesels only had a mechanical fuel pump, diesels had a better reputation for reliability than petrol vehicles but with modern vehicles the opposite is true - diesels now have more parts that go wrong (and more often) than petrol vehicles.
My son reckons his 2litre Mondeo Ghia X easily achieves over 30mpg on LPG doing mixed driving. His girlfriend owns a nearly new little Citroen hatchback with little 3 cylinder turbo diesel engine with on paper mpg of over 70. In the real world, his car costs around the same to run as the little Citreon, he didn't spend anywhere near the same money on his 2L GhiaX Mondeo as she did on the Citroen, he'd much rather have the Mondeo, she also prefers going anywhere in the Mondeo. If the little Citroen was something the type of thing he'd like to own (and if he didn't mind spending £thousands more than he spend on the Mondeo), then he'd buy the petrol version of the little Citroen hatchback (which would cost less than the diesel version), would move his LPG system from the Mondeo to the Citroen.. So if it ever came to it, his Citroen would cost him less to buy, less in fuel costs, and likely less in parts than his girlfriends...
Since the thread was started we've had 'VW&Audi-gate'
. Government had previously given a fuel cost incentive for diesels (the argument being because diesels produce less CO2).. That argument always looked invalid to LPG users (cleanest fuel of them all) because it was known at the time that diesel particulate emissions etc are more harmful to the local environment than CO2 but now government pushing diesel would seem even more silly. At least LPG users have always enjoyed extremely (in comparison) low fuel duty - and will continue to do so - duty breaks may now be less certain for any type of diesel... Not many people would concern themselves with a few% lower Britain CO2 output if full in the knowledge that diesel fumes are much more damaging to local health than petrol fumes, LPG fumes less damaging to local health than petrol or diesel - any diesel (pump diesel, bio blends, straight bio, WVO or proper bio diesel).
Figures also show running on veg oil these days wouldn't be worth the messing about, might as well run on pump diesel (particularly after reading below). Also worth repeating, most modern diesels cannot run on veg oil without great risk of damaging diesel pumps and direct injectors - Old school diesels with Bosch pumps seem to fair OK on veg oil, stuff like Transits with Lucas pumps suffer worn out diesel pumps running on veg oil. In all cases it's best to mix diesel with veg oil (reducing possible potential savings) because veg oil is thicker than diesel (even thicker in winter when a greater proportion of diesel must be used) or risk fuel starvation due to gloop in fuel lines, filters, lift pumps, main pumps.
A long time ago before I got into LPG I used to run a Ford Scorpio with VM diesel engine (before the 2.5 VM diesel version I'd had loads of 2.9 Scorpios and Mk2 Granada 2.8i's and missed the quiet, smooth power of the petrol v6's). I had the VM run on all sorts of stuff including filling the car in supermarket car parks from new 3L tubbs of veg oil, it liked the taste of cherry too! Exhaust stunk on veg oil really badly, good job it had A/C because you wouldn't want the windows open, fumes would burn your throat! Lift pump didn't like veg oil at all, had loads of probs after running on it for a while.
I looked into making 'proper' (government spec) bio-diesel, which is very different to straight WVO, looked first with a view to just making it for my own use and then with a view to producing it commercially. The thing about proper bio-diesel is that if you obtain a licence and can produce it to spec (must be made from WVO not new veg oil, must be properly filtered, must have salts and soaps removed, this involving rather dangerous chemical processes), then you could sell it at a premium above the price of normal diesel (to bus companies etc), in which case you could profit from producing it. But if you made it not quite to spec (and a government type inspector, who would be a chemist, would be checking this regularly) you would end up losing money because would have to pay more duty on it. Would probably need to employ chemists to run such an operation, and then you would find that most diesel vehicles couldn't run on your neat bio-diesel anyway unless all rubber components (O rings etc) in fuel system had been changed to metal components (100% bio-diesel corrodes rubber), so you couldn't sell it to the general public with un-modded vehicles. After learning all the above I lost interest in bio-diesel, was already fed up of stinky exhaust and other issues when running on veg oil, missed my previous petrol engine'd cars sound, power, smoothness, engine response, performance, reliability (had to helicoil rocker arm securing bolt-holes in a couple of the VM's 4 separate cylinder heads and even after that I'd occasionally have to whip the rocker cover off to pop pushrods back into rockers! It also suffered bad starting after using veg oil). At around this time I started taking notice of LPG pumps on all those garage forecourts, bought another petrol car, researched LPG a bit more, found an LPG equipment supplier who would supply me (I wasn't trade then and most wouldn't supply to none trade, it was all on the hush hush don't tell anyone we supplied you!), bought an LPG kit and converted the petrol car to LPG. Best thing I could have done! Started converting customer cars to LPG and have been doing so ever since.
Seriously - Who would prefer a clattery diesel, usually with 4 cylinders, usually with short power band, stinky exhaust unless you spend £1000's on one of the latest models (with yet to be long term tested emissions preventing technology), with greater potential of having to spend a lot more money on parts mentioned above over a petrol model, where even if engine develops same bhp as the petrol equivalent the petrol will still be more sporting and would still beat the diesel around a track... When you could have the petrol equivalent of your choosing - 4 cylinder petrol will be much more refined than 4 cyl diesel, can be converted to LPG to make cheaper to run than the diesel, comparing turbo diesels to normally aspirated petrols is like comparing apples and oranges (turbo diesel drivers should test drive the turbo petrol version of same vehicle model and see if turbo diesel holds up at all in comparison), perhaps try a smooth V6 or V8 version equivalent model and see how diesel compares then.. There is a new breed of drivers who may never have done the above, because they equate diesel with economy, yet when doing paper comparisons don't know to factor in cost of new DMF (which will break due to lumpy high low rpm torque) which may cost £1000. That £1000 spent on one prone to failure diesel engine component is money gone forever, no vehicle buyer is going to pay much more for a second hand diesel car just because it has just had a new DMF fitted - diesel car buyers are usually in same boat as other diesel car buyers (they too don't consider the potential of having to spend on a DPF etc [maybe at same time as having a new clutch fitted]). That £1000 could have been spent on an LPG conversion for the equivalent petrol model, the equivalent petrol model would probably be cheaper to buy than the diesel version, plenty of buyers will pay extra for an LPG car because it is cheaper to run than the diesel.. Even if they wouldn't spend extra for an LPG converted car, the person who had the car converted will have spent less money buying, converting and running the LPG car than the diesel car buyer. Most people are just not aware. One of the best things with LPG for many people is that it can make the difference between running a vehicle they really like (which without LPG would be too expensive to run) / compromising by running a diesel when the vehicle they'd rather own would be a petrol model, perhaps even the V6 or turbo petrol model. One of my neighbours once boasted that his diesel Freelander would do 20mpg towing the caravan fully loaded. 'Hmm', I said, 'I reckon my car would only do 10mpg pulling my caravan'. He laughed, and it still didn't quite seem to sink in when I told him that, even so, my journey pulling the caravan would cost me less than his journey since LPG was below half the price of diesel. And my car was a luxurious V12 powered BMW 750
.He was into his cars a bit, had a fairly recent model MG which he used on Sundays (not too often because he didn't like paying for the petrol), I'm sure he liked my V12. So who does it seem was compromising in terms of both choice of vehicle and fuel costs! ..We talked about the V8 version of his MG, he knew all the facts about that model and I'm sure he would have loved one.. But it never did sink in he could have run one and it would have cost him less in fuel costs than his current (not V8
) MG... That's the way it is with most people.
Hardly worth mentioning now (since veg oil is about same price as pump diesel) but new veg oil and wvo are not what the government considers bio-diesel (as explained above). Point - none government spec bio diesel attracts a higher rate of duty than spec bio-diesel - It's breaking the law if you don't pay the correct duty on the fuel you use. No worries about being dipped and having to pay a hefty fine (and maybe having vehicle confiscated too) because you haven't paid the correct duty if you run on LPG... Even if you found a very cheap supply of LPG (ahem) and ran an LPG car on it, the stuff would be indistinguishable from LPG bought from a garage forecourt.