1985 petrol Hymer 660 - should I go LPG

Discussion in 'Motorhome Chat' started by Jimmers75, Apr 1, 2012.

  1. Jimmers75


    Apr 1, 2012
    Hi there
    I'm after any advice on whether to go LPG on the 660? It's a 2 and quarter petrol engine (auto) which as you can imagine drinks fuel & having heard rumours a while back that LPG conversions did nothing but harm to the engine I've managed to resist the urge to look into it in any detail.

    That all changed after I read somewhere that the conversions these days are much better & as longas you get the right spark plugs in place, the conversion should cause no real cause for concern

    So if there's anyone reqding this who's converted something similar & can give any advice, pointers, constructive feedback I'd be most grateful

    Cheers now

  2. normanandsue

    normanandsue Funster

    Dec 31, 2010
    Dunfermline - Scotland
    Jimmy, I run a 2ltr petrol mh that was converted to run on lpg and I had problems that thankfully have now been resolved, but at considerable expense. The lpg works fine but increases my fuel consumption from 20 mpg petrol to 15 mpg gas. This still makes for reduced fuel costs even when comparing dearest lpg with cheapest petrol.
    If you go down the conversion route it is important to ensure you have your valves replaced with hardened ones as lpg burns hotter than petrol. This I had to do and it cost me, but now mh runs like a dream.

    Is it cost effective? I would say not especially on a vehicle of the age of yours, because it is unlikely you will keep the vehicle long enough for you to recover your conversion costs. Mine is effective becuase the previous owner had it done, but I will never recoup the cost of the engine overhaul I have had done.
    Hope this helps!

  3. slobadoberbob


    Jun 1, 2009
    Kent, garden of England
    you need to work out the cost v the benefits

    Cost v the benefits.. they are not cheap to fit (certainly not for a V10 yank) but it is also the extra weight of the tank and the space to fit it. Finding LPG is not always as easy as some think.. even in France in the Northern end less than the rest of the country (Motorways I refer to)...

    Plus if the engine was designed to run on LPG the makers may have offered it as an option.. never was.. so I would think twice about it.. as said value issues longer term.

    The cost of LPG 3 years ago was around 40p ltr now over 80p in most places.. so no longer cheap.. plus again as stated less miles to the ltr... means filling up more often.

    It is a balancing trick.. some swear by it other have looked into it and decided it takes a long time to get the costs back...

  4. darklord


    Apr 28, 2011
    I have convered landrovers to run on LPG. If you are looking at cost, whether you will get a return for your money, and whether it will be relativly trouble free, the answer to all of the above...is no.

    Look at the equipment itself, you need room in the engine bay for a vapouriser, the pipework, and solenoids,....THEN, you need a tank. An 80lts LPG tankis about two foot six inches, by eighteen inches, by eighteen inches high, it has to be securely bolted in, and forms part of the mOT. For a MH, you would go for underslung tanks, which would be found in a size that suits your vehicle, BUT, the above mentioned tank.......will only give you just over 100 miles of travel, as they can only be filled to 80%.

    The above work will have to be done by an accredited fitter, who will have to supply a certificate that YOUR insurers are happy with.
    As has been said, LPG runs leaner, so valves will burn out if they are not suited to unleaded petrol, PLUS, when switching back to run on petrol,..you may have pinking/overunning/overheating problems.

    In my honest opinion, LPG conversions are suitable only for large US engines, and small petrol en gines with electronic fuel injection set ups...certainly not a car with a carb, unless you are a mechanic.
    Again, in my honest opinion, you would be much better off, finding a diesel conversion for you motor. It could be done by any competant garage, cost less, and there will be no mysteries to it. It will also give you the advantage of having an engine with a torque band moe suited to pulling a motorhome.
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  5. aba


    Oct 27, 2009
    in reality you would be better finding a diesel motorhome or just stay as you are.

    at the moment petrol is cheaper than diesel and i assume you will be getting around 20mpg. so at £1.41 per litre it costs 32p per mile. which equates to 21.5mpg from a diesel at £1.51 per litre.

    the cost of swapping from a petrol to a diesel can be more than the gas conversion.
    as not only the engine would need to be changed .
    you may find that the petrol gearbox wont fit and the rear axle would probably be the wrong ratio for a diesel, you would also be advised to change the fuel tank or at least the tank sender unit as this would have the correct pipework but again may not fit the petrol tank.
    and then the engine wiring loom that would most likely need changing along with adding the necessary heater plug relay etc.

    dont be fooled into thinking that its as simple as just bunging an engine in and changing the fuel.
  6. callumwa


    Jan 16, 2011
    Tyne & Wear, sometimes..
    I think you will struggle to see any real benefits. The overall costs, modifications, weight, etc will outweigh the benefits, certainly financially.

    Also remember the LPG prices are rising. I feel it is only a matter of time until the Government increases taxes and edges them ever closer to petrol and diesel prices. I have also spoken with a lot of folks on the continent who are also complaining about LPG prices rising dramatically.
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  7. rainbow chasers

    rainbow chasers

    Oct 30, 2009
    Mid Cornwall
    First things to consider is fuel prices. Currently, a petrol vehicle is becoming more economical than diesel to run as diesel prices are rising above petrol prices to a degree where the economic advantage of diesel is falling fast.

    You then have to work out the cost advantage of lpg, tax reductions and possible emission advantages depending on where you live to work out the benefits - also, do work out your flatline (where cost of lpg/mile equalises with petrol - genrally, this is around 88p)

    Now we go onto the vehicle;

    Carburettor models - the benefits are minimal as the carb wastes fuel. You may find an increase in economy of around 3-7mpg - which to be perfectly honest, you could eaily acheive with fuel efficient driving habits.

    If Injection - then there will be benefits to be had as it burn efficiently. The benefits vary, according to the system you buy - and you get what you pay for! A cheap single point will offer a little benefit, a cheap multpoint may be underpowered and thus offer not so much as a premium system. The premium system does not mean if needs to be expensive...all it means is a multi point sequential system that has the power capacity to meet your engines requirements....many will put a cheap 200bhp system onto a vehicle that has 360bhp...which mean they can cruie and knock about town, but develop a 'flat spot' when they wish to overtake.

    Gas burns hotter, so wear on your valve seats will occur - but they are inline oilers that will replace the lubricant usually supplied my petrol, avoiding the need of valve seat hardening.

    Gas also burns cleaner, so can play havoc with your vehicles sensors.....lambda sensors may cause your engine light to come on - don't go rushing to the garage - ignore it as it will oly come on whilst on lpg. The reason it does this, is because the sensor reads no carbon, or a limited reading of carbon passing, so the ecu thinks it must be faulty. Go back on petrol and it reads just fine! Soething you will get used to.

    All in all, I would suggest you think about how often you use the vehicle - if regularly, and the vehicle is a suitable injected model, then investigate further and even fit yourself, takig to a fitter to check and issue a certificate after.

    If it is only occasionally, or the vehicle is carburetter, then I would suggest not bothering and deal with the fuel cost other ways, such as fuel effiicient driving, or saving supermarket 5p off/litre vouchers for your holidays.
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  8. JJ

    JJ Funster

    May 1, 2008
    Quinta Majay, Pinheiro Bordalo, Portugal
    I would be very surprised to find an ECU on a 1985 Hymer 660 :Eeek:

    Hymers were ahead of their time I know but this would be a bit much even for them! :ROFLMAO:

    JJ :Cool:

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