changing to a petrol engin with gas conversion (1 Viewer)

Nov 18, 2011
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just been speaking to sumeone who could not get a 2.5td engine for his camper but managed to get a petrol engine he has just put it in with a gas conversion would it be worth it and how much would it save on fuel
and running cost
 

golly

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I know its not the same, but I have a 2.5 petrol Subaru outback, I had a gas conversion done a few years ago. On petrol I get about 28mpg, on gas I get about 23mpg but am only paying £0.66p a litre for gas.
 

Tootles

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I know its not the same, but I have a 2.5 petrol Subaru outback, I had a gas conversion done a few years ago. On petrol I get about 28mpg, on gas I get about 23mpg but am only paying £0.66p a litre for gas.

I'm running a Subaru 2.5 Legacy Outback estate on LPG, and I'm getting the same MPG as with petrol...........???

Maybe your gas setup needs a check??

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Sep 30, 2012
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I feel such a saddo knowing this but I only know as we also have a converted LPG Jeep.

LPG has only 80% of the calorific value of petrol so you will always get a slightly lower MPG, but the good bit is it is much cheaper. :thumb:

Nicky
 

Tootles

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I feel such a saddo knowing this but I only know as we also have a converted LPG Jeep.

LPG has only 80% of the calorific value of petrol so you will always get a slightly lower MPG, but the good bit is it is much cheaper. :thumb:

Nicky

Well, this is strange. This is my 3rd LPG vehicle. The first was a Series 2 LandRover, on petrol 18 or 19MPG. on gas, 22mpg.
The second was a Jeep Cherokee 4ltr. That did more to the gal/ltr then on petrol.
And the Scuby as I said, is doing the same, if not slightly more. The Jeep and the Scuby were/are both auto. Puzzled.

However, on all three I have noticed a distinctive loss of power on hills.

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pappajohn

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Well, this is strange. This is my 3rd LPG vehicle. The first was a Series 2 LandRover, on petrol 18 or 19MPG. on gas, 22mpg.
The second was a Jeep Cherokee 4ltr. That did more to the gal/ltr then on petrol.
And the Scuby as I said, is doing the same, if not slightly more. The Jeep and the Scuby were/are both auto. Puzzled.

However, on all three I have noticed a distinctive loss of power on hills.

how do you check your mpg.....wait until it runs out then 'brim' it or judge by the cost per fill if frequent part top up.

As stated, lpg is 20% less efficient than petrol so cannot return a higher mileage for the same driving style and road conditions.
My rv consistantly returns 10mpg on petrol and 8mpg on gas using empty to full as a calculator.

The loss in efficiency is very rarely noticed as a loss of power as the engine is working slightly harder to compensate.
 
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enery8

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towing for 20 odd years but now have our first motorhome.
I had a V8 3.5 litre range rover on LPG and it ran better on LPG than on petrol. Better mpg as well.::bigsmile: I would certainly consider a camper/motorhome on LPG after running my old rangy on it.:thumb:
 
Feb 24, 2013
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if a lot of your journeys are short you must factor in the miles you do on petrol before the LPG switches over. We run a Land Cruiser with LPG conversion, in winter doing about 1 mile to work and 1 mile home we hardly use any LPG, just petrol!!

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jaytee74

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changing to a petrol engine with gas conversion

in my experience well worth doing no difference in performance no engine wear need never change engine oil as engine runs clean all advantages providing it is set up properly i have converted two 1.9 petrol engine ducato motorhomes and done big milage with them touring europe if i had been running on petrol i could not have afforded it but running on LPG reduced my running costs by 40%. now a word of caution if you use a firm to supply and install a basic single point system its going to cost approx £1000 to £1200. if you buy the system and install yourself the cost would be in the region of £700. to justify that sort of cost you have to do the milage to offset the cost if you are not going to do the miles then it is hardly worth doing. anyway thats my sixpenneth. jt.
 
Aug 6, 2013
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if a lot of your journeys are short you must factor in the miles you do on petrol before the LPG switches over. We run a Land Cruiser with LPG conversion, in winter doing about 1 mile to work and 1 mile home we hardly use any LPG, just petrol!!

Ask your installer to re-programme to start on LPG. The only reason that these systems start on petrol is to ensure that the petrol system is kept fresh (to prevent varnish / stale fuel build up in the injection system). You can do that yourself by running on petrol briefly once the engine is up to temperature.
 
Aug 6, 2013
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just been speaking to sumeone who could not get a 2.5td engine for his camper but managed to get a petrol engine he has just put it in with a gas conversion would it be worth it and how much would it save on fuel
and running cost

Normally I'd say yes but if the engine option is the 2 litre normally fitted to Fiat / Talbot Express vehicles then no. I have experience of both: I converted my 2 litre petrol Talbot Express to LPG and the financial gain was well worth it BUT it turned an already gutless engine (around 60 - 70 hp on petrol) into something that was no pleasure to drive at all. The van that followed was based on the Fiat 2.5TD which, at 90+ hp IIRC, transformed the experience. Replacing a 2.5td with a 2 litre petrol would reverse the experience. It isn't something I would ever contemplate doing.

You can normally assume a 50% cost saving by converting to LPG.

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pappajohn

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Ask your installer to re-programme to start on LPG. The only reason that these systems start on petrol is to ensure that the petrol system is kept fresh (to prevent varnish / stale fuel build up in the injection system). You can do that yourself by running on petrol briefly once the engine is up to temperature.

the main reaason for starting on petrol is to ensure the vapouriser is of a proper temperature to fully turn liquid propane to a gas.
the vapouriser is heated by the engines cooling water

while it will start on lpg it wont be as efficient as it could be until it has warmed the engine.

depending on ambient temperature mine takes around 10 minutes on petrol before switching to gas..
 

Terry

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Why are you changing ? thought you had rebuilt your engine ?
terry
 

Terry

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Is it a 2.5 td engine from a old ducato your after? I can ask my mate to find one if you want ? He found one for a member about 6 mths ago -
terry
 

MikeD

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2.5TD engines

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Bill

There is a couple engines on ebay - any good? The second one has been on sale for months and months though!

Mike:thumb::thumb:
 

Tootles

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Quick Bill, JUMP IN!!! ::bigsmile:

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Bill

There is a couple engines on ebay - any good? The second one has been on sale for months and months though!

Mike:thumb::thumb:
thanks mike sent text to one of them and phoning the other Monday cheers bill:thumb:
 
Aug 6, 2013
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the main reaason for starting on petrol is to ensure the vapouriser is of a proper temperature to fully turn liquid propane to a gas.
the vapouriser is heated by the engines cooling water

while it will start on lpg it wont be as efficient as it could be until it has warmed the engine.

depending on ambient temperature mine takes around 10 minutes on petrol before switching to gas..

Propane boils off at -40 degrees C and therefore requires no additional heat to fully vapourise. The reason for heating the vapouriser (more correctly the converter / regulator) is to prevent water vapour in the atmosphere condensing on its working parts then freezing. "Cold" engine coolant is more than warm enough to do this. Starting on petrol has all the usual disadvantages: increased bore wear, oil dilution (neither of which are anything like the problem they were with carburettor engines), and excessive consumption.
 

DBK

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I don't think so. The difference is a petrol (and diesel) engine runs on a liquid fuel. Although it may be in the form of very small droplets at the time of ignition, it is still mostly liquid, particularly for fuel injected engines. In an LPG engine the liquid fuel (the LPG) evaporates as it is drawn into the engine and this is what cools it and can result in ice forming from the water in the air. It is precisely because the LPG is so volatile that it starts to evaporate as soon as it released from its compressed state, thus reducing temperatures in the inlet, just as in a refrigerator. Nothing changes from a liquid to a gas without heat coming from somewhere.

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cmcardle75

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Propane boils off at -40 degrees C and therefore requires no additional heat to fully vapourise. The reason for heating the vapouriser (more correctly the converter / regulator) is to prevent water vapour in the atmosphere condensing on its working parts then freezing. "Cold" engine coolant is more than warm enough to do this. Starting on petrol has all the usual disadvantages: increased bore wear, oil dilution (neither of which are anything like the problem they were with carburettor engines), and excessive consumption.

Actually, the natural evaporation rate of propane in a typical vehicle tank is far too slow to run even a small engine. Even running propane heating can be iffy in cold weather and that might require the vaporisation of your tank of gas over a week, whilst the engine wants to vaporise the lot in a few hours, so needs orders of magnitude more evaporation.

The vaporizer needs to force the issue by putting far more heat into the process via the engine coolant than would be absorbed naturally by the tank.

This is why a vehicle LPG tank has a liquid take off at the bottom, to get liquid fuel to the vaporiser, whilst heating/fridge/cooking takes the vaporised gas off the top.

Although why LPG injectors don't just atomise the fuel like petrol instead of vaporising first I don't know.
 

DBK

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Although why LPG injectors don't just atomise the fuel like petrol instead of vaporising first I don't know.

'Cos it's boiling point is -42C or thereabouts at atmospheric pressure so it immediately wants to change to a gas when the pressure is released, for which it needs heat from somewhere and the surrounding air is the most convenient.
 
Aug 6, 2013
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The LPG vapourises as it leaves the converter/regulator at the much reduced pressure required by the engine. The converter/regulator has to supply the heat. The heat it requires is (or can be) drawn from the cold, circulating, coolant. If there was no coolant connection to the c/r it would fail due to the build up of ice on and inside the device. The (engine) coolant does not need to be heated above ambient to keep the c/r free of ice.

This discussion assumes that on any converted vehicle petrol will be available to start: this simply is not the case. My 2 litre petrol Talbot certainly didn't have petrol available and I have been involved in two similar conversions.

The point about needing liquid to provide enough fuel to run the engine is valid but it isn't the gassing-off rate that is the issue it is the restriction of the pipework and increase in size of off-take at the tank that would be needed. Passing the fuel in liquid form to as close to the engine as possible means pipework can be kept small & easy to route until after the converter/regulator.

Liquid LPG injection has been tried but has not, to date, been successful. The issue is keeping the fuel as a liquid until it is ready to be injected. The LPG tank is in a relatively cool (or at least at outside air temperature) location & at that temperature the vapour pressure is around 10 bar. Temperatures in the engine bay can easily exceed 100 degrees C at which the vapour pressure rises to 30 - 35 bar. When a vehicle is parked after a motorway run the engine bay temperature rises well above that. The fuel pump, injection pipework, and fuel rail regulator would be required to maintain a pressure well in excess of 35 bar (possibly double) to ensure that the fuel remained as a liquid.

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cmcardle75

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'Cos it's boiling point is -42C or thereabouts at atmospheric pressure so it immediately wants to change to a gas when the pressure is released, for which it needs heat from somewhere and the surrounding air is the most convenient.

That makes sense, although it is a shame, as the cooling effect would make for some free intercooling if it could be managed properly, which clearly it can't!
 
Aug 6, 2013
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:Smile::Smile: I've read that too. Because it's written doesn't mean it is correct. To freeze the c/r as they're suggesting means that all the engine coolant, the radiator, and the engine itself would need to be below freezing point and would have to remain in that condition for some time after the engine is running. I'm sure it COULD happen under very specific conditions ............... but it just doesn't. Their point about keeping the petrol system working and clean is the important result of starting on petrol.

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cmcardle75

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:Smile::Smile: I've read that too. Because it's written doesn't mean it is correct. To freeze the c/r as they're suggesting means that all the engine coolant, the radiator, and the engine itself would need to be below freezing point and would have to remain in that condition for some time after the engine is running. I'm sure it COULD happen under very specific conditions ............... but it just doesn't. Their point about keeping the petrol system working and clean is the important result of starting on petrol.

That is quite interesting. I'm using rather too much petrol at the moment. I have an electronic ECU type top end lubrication system, so don't need petrol for valve lubrication. However, I'm using a tank of petrol every 2 months, which is too much (I fill the LPG tank every 3-4 days) and I'm guessing I could use a 1/10th of that without the petrol injection system gumming up. The system can be forced to start on LPG. Do you think I should risk it? At least when the temperature is around 10C?
 

cmcardle75

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That is quite interesting. I'm using rather too much petrol at the moment. I have an electronic ECU type top end lubrication system, so don't need petrol for valve lubrication. However, I'm using a tank of petrol every 2 months, which is too much (I fill the LPG tank every 3-4 days) and I'm guessing I could use a 1/10th of that without the petrol injection system gumming up. The system can be forced to start on LPG. Do you think I should risk it? At least when the temperature is around 10C?

P.S. This is for my car, which is a Toyota VVTLi 1.8 190PS. The RV has a rather agricultural carb fuel system which has very little in common with an electronic petrol/LPG multi-point injection system. That wouldn't idle at all on LPG until it has warmed up.
 
Aug 6, 2013
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P.S. This is for my car, which is a Toyota VVTLi 1.8 190PS. The RV has a rather agricultural carb fuel system which has very little in common with an electronic petrol/LPG multi-point injection system. That wouldn't idle at all on LPG until it has warmed up.

There's no risk - just do it. Don't run on petrol at all until the engine is at running temperature & then only for a few seconds. All the petrol system needs to do is flush through with fresh fuel from the tank - that takes no time at all.

Carb systems do need a fast idle for a brief period when starting on gas. On the last one I did I simply removed the choke flaps so the normal choke fast idle worked without the actual choke operating.

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