Mpg was about 15% worse than gas, across the range. Really heavy footed driving would get me about 15 mpg, and my average was 18 or 19mpg. Cruising for long distances at a steady 70 mph I would get 25 To 27 mpg. Remember, I am talking of UK gallons. Over my perion of ownership, using the car as my daily driver I have saved many thousands of pounds on fuel. I actually smile when I pay for the propane!

No detectable difference in performance whatever. As before, when I get the new system installed, I will have a lubrication system put in. This drips a special light oil into the cylinders, and is supposed tp protect the valves.

 

Diddion,
I would like to ask about your consumption, too, i have just bought a 4 litre XKR, 2002 model, and intend to get it converted. I have run cars on LPG for the last 18 years and saved a fortune! My Saab 9-5 aero does about 20 mpg around town on petrol, but on LPG around 16, which sounds terrible until you see that LPG costs 52.5p per litre at the moment compared with £1.18 for petrol. This equates to about 35mpg, which of course is amazing for a big and powerful car, but on a run I get the equivalent of over 60MPG! I am getting about 18 to the gallon so far from the XKR so i fully expect that to be more like 14 on LPG, which would be amazing at 52.5p per litre, but i would like to hear of your experience and i'm sure it would help others on here! Thanks in advance!

 

Hi Spider589. I constantly measure this, generally full to full, but occasionally full to empty. With normal (ie not particularly sedate!) driving a full tank of 61 lites wouild get me about 210 miles; this works out at about 15.5mpg. On a long, steady haul (such as across Spain to Portugal) I have achieved up to a real 25mpg or even a tad more, when keeping a steady 70mph. Generally, on a long-ish steady journey, 22 to 23mpg is readily available.

Two interesting points. You'll find that the real fuel consumption is about 15% poorer than the computer says. I believe that the computer measures fuel flow, but the real consumption is higher because lpg has a proporionately lower calorific value. So the computer would be correct-ish if you were on petrol. Any forum members able to correct my explanation, or agree with it, please do comment!

Second, worth bearing in mind is that the first mile or two on a cold engine is always on petrol, so the figures will be distorted: none of the lpg converters focus on this! The result is that for a short journey you will use less lpg - but only because you are using petrol! Here is a spot of maths:

10 separate journey, from cold, of 10 miles. We'll assume that the first 2 miles of each journey are on petrol. Hence of your 100 miles, 20 will be on petrol, 80 on propane. If your actual propane consumption is 16mpg you will use 5 gallons. But you will have covered 100 miles in total, and your straightforward calculation could be 5 gallons for 100 miles -so 20 mpg. Wrong! 20 of this was on petrol!

This time you do a single journey of 100 miles, of which 98 are therefore on lpg. Again, we'll assume 16mpg. Well, that 98 miles will use 6.125 gallons. Once more, you do your caculations, and once more you ignore the petrol. So you assume all 100 miles on propane. This time the calculation becomes 100/6.125, which is a tad over 16.3 mpg, as calculated. Still slightly optimistic, but nowhere near as wrong. Of course, longer journeys and shorter breaks, so the engine is not dead cold, bring you even closer to the accurate result.

Serious apologies for the maths lesson. I used to be a science lecturer, and it does remain in the blood! Get back to me if me explanation is not clear.

Finally, I am completely convinced of the value of propane for these cars, especially if you are not in the millionaire class and use it as a daily driver. Essental to use a quality system wih upper cylinder lubricant, and have it fitted by competent people wth good reviews, unless you have personal knowledge of an expert.

Hope this helps.

 

Additional note: Some purists object to lpg for the Jag. There is no evidence of which I am aware that there is any damage to the engine; it may even be protective. Overall with cleaner emissions, it is more environmentally friendly (or, more honestly, less environmentally unfriendly!). And at the end of the day you can remove it if you want to return the car to original spec.

 

I would probably never switch to LPG (93 octane is $2.50/US gallon), but all reports are that motors could last longer on it.

Thanks for the detailed information on this subject. It helps with understanding the pro/cons.

 

Thanks, Ungn. Probably worth a trip across the Atlantic to fill up the tank.

 

Thanks, Diddion, for the very informative and helpful information, which backs up what i was thinking! For anyone considering the conversion to LPG this might prove helpful. So far, after about 600 miles since i bought it, my XKR is doing allegedly 18.3mpg overall. this is mostly "round town" with a few 5-10 mile journeys to improve the average! on these journeys it seems to be around 21-ish.
So, as this seems to concur roughly with your stated consumption, we can say that every 1000 miles (at 18.3mpg) is going to use around 54.64 gallons of petrol, which at the price I am paying of around 117.9p per litre or £5.35 per gallon means £292.46
If i get 15.5mpg on LPG, that equates to 64.52 gallons of gas, or 293 litres, which, at 52.9p per litre is £154.95, saving £137.50 for every 1000 miles.
So, depending on where you go to get the LPG conversion done, it is going to be paying for itself only if the car is to be kept for a fair few thousand miles! I have had 2 quotes, one at £1900 and one at £1300. Of course the higher priced one claims that anyone who is cheaper than him is going to use inferior parts and cut corners, but the lower price happens to have come from the company who fitted my LPG conversion on the Saab Aero (for the previous owner about 8 years ago) and it is the most seamless conversion i have driven, going onto gas after a few hundred yards in the warmer months, maybe a mile in the depths of winter, and running superbly!
To conclude, I will probably do about 10,000 miles per year so it is a no-brainer for me, even if i go with the more expensive conversion i will have paid for it in 17 to 18 months, (10 if i go for the cheap one!) and from then on I am going to save £1375 per year. I am fortunate that where I go for my LPG has an additive to eliminate the Valve Saver, but i don't know how prevalent that is around the country. I can only say that my Saab has never had any Valve Saver added in 6 years and it's still going strong!
Hope this helps anyone who is considering LPG! (if you can follow my meanderings!)

 

Hi Spider589. Yes, I think our figures match, and I reckon I saved between £1500 to £2000 a year so, even after conversion costs, this has made a huge difference to overall running costs.

I am not sure that I would agree with your views on valve saver. This costs virtually nothing to add to the conversion, and you can leave the fluid container empty if you really wish. At worst, it won't do any harm, and at best it may protect the valves. As far as cost is concerned, the going rate seems to be £1800 to £2000 nowadays (2017) which is somewhat less than the (I think) £2500 I paid back in 2011. I believe the systems are better now, as well, but it may be that the difference in cost you have come across is accounted for by difference in the price of the different kits.

Be careful on this one! £1300 is a very good price, clearly, and it makes sense not to pay more than you need. So do check with them which system they will be using and maybe do some google research on them; the more expensive people say that the cheaper system is not so good - yes, may be purely marketing, but also may be right! Cheaper systems can give rise to problems such as slow filling and inadequate lpg feed to the cylinders, and I don't know if they are as robust. Also, I would go for the firm that has done one of these on an XKR, so they should have ironed out any installation issues with the model.

Mine was done with the BRC system - one of the more expensive ones at the time, but well thought of. BRC is no longer in existence (don't know if that tells you anything!)
Can you report back on the systems you are considering? This will be very interesting.

 

Yes, i'll keep you posted when i get the full info on the alternative systems!

 

Posted in another thread, but answered here, since this will be a more appropriate place and more likely to be read by others interested in the conversions:

Propane is filled as a liquid under pressure, using nozzles similar to petrol nozzles. The main difference is that the nozzle has to be properly attached to the filler (and hence sealed) and the user has to lean on a button all the time in order to operate the pump - propane users are not just being lazy when they are leaning on the pump!

The cost of filling has been dealt with further up this thread, but in principle we are talking about £30 or so.

Let me say something about the lpg tank. This is in addition to the normal fuel tank and fuel system, which remains fully operational within the car. This must be so, because the car needs petrol to start up, and the switchover to lpg only happens when the engine is warm. If you run out of lpg, the car will automatically switch back to petrol - note that the car will now become bi-fuel, not just lpg or just petrol.

The tank sits in the spare wheel well, so the spare wheel will take up boot space (unless you choose to dispense with it and use one of those temporary repair foam systems - though I don't think that is wise!) If you have, for example, 280 miles available on a full tank of petrol, and say 220 miles available on a full tank of lpg - then you could go some 500 miles before having to stop.

There is no detectable difference in performance between the two fuels. Let me know if you have any more questions!

 

Good info Diddion. Sorry about the loss.

 

I have my XKR 4.2 at LPG for at least 5 years and it works fine. Furthermore the engine is also boosted but there is no problem. The power is very similar to when it is powered by gasoline but the savings are remarkable, my car is considered "ecological car" for the Italian regulations, I have a 40% discount on the stamp and is better for the environment! great I'd say!

TOP GEAR magazine Italy write about this system on my car. (You can see my car as it fills the LPG )