LPG math

[Richard Fixter]

My Rx has been on lpg for 7 yrs about 60000 miles I drive it quite hard and return about 28mpg on a run I fill up mostly at asda at 52.7 p per litre ,the best thing about lpg is that when you really want to boot it you can do so relatively cheaply especially out dragging mercs and bmw's I don't really worry too much about mpg because I have worked out that the saving has bought the lpg conversion and about half of the purchase price of the car. Average mpg on lpg is about 19 mostly on short journeys. I only ever put £15 worth of petrol in the tank about once a month to keep the fuel fresh. 

If your only concern is ROI that will depend how long you intentend to keep the car and annual mileage. The other thing to take into consideration is the cost of flashlube that must be fitted not expensive adds about  1p a litre. 

If you do go for it avoid the done in a day or two guys mine was away for 5 days .

Hope that helps at the end of the day it's up to you,I haven't regretted it and although I want to change to a rx450h I will keep this one till it dies,just changed the plugs and cam belt, just the transmission fluid left to do.I would get the plugs done before the change the iridium plugs I fitted 60k ago looked pretty good but the gap had widened a little.

 

I would say go for it.

[m4rkw]

https://m.rkw.io/lpg.html

Those defaults are my numbers. I put 12L of petrol in based on your post (£15 at £1.25/L).

More than 2 years to break even seems like a bit of a risk, so many things could happen in that time to ruin the investment.

[Herbie]

Most people, including myself, just look at the money but we haven't mentioned two other benefits yet.

LPG is much better for the environment, so it's one more thing to help save the planet for your kids.

LPG is much better for the engine. Oil comes out after 9000 miles almost as clean as it went in, which has got to help with longevity.

[m4rkw]

16 minutes ago, Herbie said:

LPG is much better for the environment, so it's one more thing to help save the planet for your kids.

I’m not convinced it’s *that* much better. It supposedly produces 20% less CO2 but that’s somewhat offset by the efficiency loss which apparently can range between 5-20%. The lack of particulate emissions is certainly good in cities, but we’d do a lot more to “save the planet” by taking trains and walking instead of driving a big heavy SUV around. Even switching to a small efficient hybrid car would likely do a lot more to reduce CO2 emissions.

None of us are likely too keen on those ideas though :). And hey if anyone reading this feels like sponsoring me to “save the planet” by converting my RX to gas please don’t let me stop you!

[genius149]

4 hours ago, Richard Fixter said:

 The other thing to take into consideration is the cost of flashlube that must be fitted not expensive adds about  1p a litre. 

I'm not sure that flashlube is essential.  I've seen a few discussions on here about it and possibly because I'm looking to get an LS, the V8 might not need it but my mk1 LPG GS didn't have it and didn't need it either.

The other thing to consider is that it might well add a bit to the sale price when you come to sell it.

[m4rkw]

Reconsidering again in light of these claims: https://www.dynamicassetrecovery.com/whats-best-lpg-petrol-or-diesel

"LPG produces 33% less CO2 emissions than petrol and 45% less CO2 than diesel. LPG vehicles produce up to 82% less Nitrogen Oxide pollutants than petrol and 99% better than diesel ! 63% less Carbon Monoxide. 40% less Hydrocarbons than petrol and 70% less than diesel. 50% less particulates than petrol and 98% less than diesel."

[royoftherovers]

Get a life Mark.......buy a bicycle !

[m4rkw]

4 minutes ago, royoftherovers said:

Get a life Mark.......buy a bicycle !

Hey come on now.. we're all friends here. There's no need for language like that.

[Bluesman]

19 hours ago, genius149 said:

I'm not sure that flashlube is essential.  I've seen a few discussions on here about it and possibly because I'm looking to get an LS, the V8 might not need it but my mk1 LPG GS didn't have it and didn't need it either.

The other thing to consider is that it might well add a bit to the sale price when you come to sell it.

If your vehicle runs on unleaded fuel then there is no need for flashlube and any installer who tries to sell you one is untrustworthy.

 

[m4rkw]

1 hour ago, Bluesman said:

If your vehicle runs on unleaded fuel then there is no need for flashlube and any installer who tries to sell you one is untrustworthy.

Interesting. Can you link me to a technical explanation of this? My local installer said japanese cars need it.

[m4rkw]

Internet says the need for flashlube is because of soft valve seats on japanese (and other) cars. What does that have to do with unleaded?

[m4rkw]

https://forums.whirlpool.net.au/archive/2705805

Thats the engine I have..

[Bluesman]

27 minutes ago, m4rkw said:

Internet says the need for flashlube is because of soft valve seats on japanese (and other) cars. What does that have to do with unleaded?

Because to use unleaded petrol you need hardened valve seats and this is also needed for LPG use.

[Bluesman]

59 minutes ago, m4rkw said:

Interesting. Can you link me to a technical explanation of this? My local installer said japanese cars need it.

Your local installer is talking rubbish and trying to get an extra £100 for no good reason at all.

[Herbie]

31 minutes ago, m4rkw said:

Internet says the need for flashlube is because of soft valve seats on japanese (and other) cars. What does that have to do with unleaded?

Lead was used in petrol to improve performance, lower fuel consumption and also as a valve lubricant. When lead was banned and with the advent of unleaded petrol, manufacturers started using hardened valve seats to compensate for the lack of lubrication, so in theory the hardened valve seats should be able to cope with the higher temperature of LPG combustion.

The problem is, there is no industry standard for the 'hardness' of the valve seats, so some engines will inevitably have harder seats than others. The softer the valve seat, the more prone to problems.

If a manufacturer was producing LPG-fuelled cars in the factory then they would obviously use suitable valve seats at the outset, but we are talking about converting engines that were originally intended to run on petrol.

Did Toyota/Lexus develop these engines with a view that someone may convert it to run on LPG later in its life and therefore fit it with suitable valve seats? The problem is that no one knows for sure and can say with 100% certainty that they did, so for the small extra cost of Flashlube I would not take chances with my engine and I would use Flashlube.

[Bluesman]

28 minutes ago, m4rkw said:

https://forums.whirlpool.net.au/archive/2705805

Thats the engine I have..

For that to make a proper example about how one is better than the other is to have measured the valve seats at the time the LPG install was done and this wasn't so the figures are meaningless.

[Bluesman]

4 minutes ago, Herbie said:

Lead was used in petrol to improve performance, lower fuel consumption and also as a valve lubricant. When lead was banned and with the advent of unleaded petrol, manufacturers started using hardened valve seats to compensate for the lack of lubrication, so in theory the hardened valve seats should be able to cope with the higher temperature of LPG combustion.

The problem is, there is no industry standard for the 'hardness' of the valve seats, so some engines will inevitably have harder seats than others. The softer the valve seat, the more prone to problems.

If a manufacturer was producing LPG-fuelled cars in the factory then they would obviously use suitable valve seats at the outset, but we are talking about converting engines that were originally intended to run on petrol.

Did Toyota/Lexus develop these engines with a view that someone may convert it to run on LPG later in its life and therefore fit it with suitable valve seats? The problem is that no one knows for sure and can say with 100% certainty that they did, so for the small extra cost of Flashlube I would not take chances with my engine and I would use Flashlube.

LPG runs at a lower temp than petrol. I don't know of any engine that has been wrecked because of the use of LPG without flashlube. I have run German, English, Sweedish,  American over 16 years on my cars and my wifes cars I also know of several friends cars who have also run on LPG with no flashlube and not a single one of them has ever come to grief.

[m4rkw]

This seems to be a UK company that have stopped doing LPG conversions entirely (on any car) specifically because of valve seat wear: http://www.amrautos.co.uk/index.php/lpg-systems

[m4rkw]

A data sheet from Prins is linked there with a list of cars/engines that see valve seat wear: http://www.amrautos.co.uk/database_problem_cars.pdf

[m4rkw]

It doesn't specifically list my engine code but it says that Toyota Corollas from 2004+ report valve seat wear even with flashlube.

[m4rkw]

More evidence that this might not be a good idea on my engine: https://www.toyotaownersclub.com/forums/topic/110278-can-vvti-be-convertible-to-lpg/

[Bluesman]

52 minutes ago, m4rkw said:

This seems to be a UK company that have stopped doing LPG conversions entirely (on any car) specifically because of valve seat wear: http://www.amrautos.co.uk/index.php/lpg-systems

That was written a long time ago. I pay 50p a litre for LPG and petrol is £1-29 a litre, nowhere near the prices written in that report. The write up has the feel of a garage that is not getting the work any longer. There are still manufacturers out there happily producing dual fuel cars. 

When I first decided to get a car converted to LPG I heard all the experts mainly in pubs saying, it will wreck your engine, you will never get your money back, it will always go wrong, the government will up the price of lpg by loading it with as much tax as petrol and many more as well. 18 or so years later that 1996 Mercedes Estate 200 which a friend of mine now owns still running coming close to 300,000 miles on the clock on the same engine (no rebuild) same gearbox etc. So I will go with the info that I have learnt over the years and the evidence that I have seen and experienced with my own eyes.

[m4rkw]

@Bluesman Why would Prins release a long list of cars known to experience valve seat wear on LPG if it wasn’t so? It’s completely at odds with their core business.

[m4rkw]

Someone on this very forum apparently had valve wear: 

 

[Herbie]

2 hours ago, m4rkw said:

More evidence that this might not be a good idea on my engine: https://www.toyotaownersclub.com/forums/topic/110278-can-vvti-be-convertible-to-lpg/

What does it say on my valve cover? I'm sure I can see "VVT-i" there - or do I need to go to Specsavers?