Car LPG conversion. advice etc

You use more gas than you do petrol so your mpg actually drops. It's the difference in price per litre that gives you the savings. Find a commercial gas filling station near you if you can - saves a few pennies per litre over Shell/BP. An easy way to do this is to find taxi that use LPG (loads do around Bolton) and find out where they fill up - I'll bet you it ain't at a mainstream petrol station forecourt...

Get used to checking online for LPG filling sites when you're travelling any decent kind of journey lol. Always call the station to check they still do LPG/Autogas - much online info is out of date (!).

My BMW 330 is on LPG and I get about 24-25 MPG on gas (official MPG is 31). At normal petrol prices 1,000 miles should cost me around £213. Running on LPG it costs me about £126 (so roughly 40% cost saving).

There are differences between petrol and LPG combustion. Petrol burns hot momentarily and is then done. LPG burns at a lower temperature but the exhaust gases retain more heat. This means that when the exhaust valves open in an LPG-fueled engine the valve seats get a harder life than engineers planned for (due to the exhaust gases passing over them being much hotter than intended) and can dry out/overheat. This is what used to cause most of the problems in earlier LPG-fueled vehicles. Some manufacturers fitted hardened valve seats by design from the factory for longevity and these engines are generally better suited to LPG than others. One such manufacturer was BMW, which is why I opted for a Beemer for my LPG experience. There is an alternative for engines without hardened valve seats called a Flashlube kit which effectively lubricates/cools the valves/cylinder head, protecting the engine. More info here: http://www.flashlube.com/gb/products/valve-saver-kit.html

Another thing to consider is that the LPG acidifies the engine oil. It also has far, far, farrr less crap in it that liquid fuels so the oil doesn't contaminate and go brown/black so quickly. This has caught many people out, who think that they therefore don't need to change their oil so frequently. The result is that the acidification of the oil plus the longer time between changes causes vastly accelerated component wear. Simple solution - change your oil more frequently. Oil service intervals for my 330 are 15,000 miles - I change it every 7,500 miles just to be safe.

Be absolutely sure that your cooling system is in tip-top condition too. LPG will put a heavier strain on it. A well-maintained and efficient cooling system should have no problem, but one that's old and tired may prove inadequate.

A lot of conversions have the filling point installed in the wing of the car. Be very careful of this - the vast majority of these installations get bad rust around the filler cap simply because the metal is simply cut, touched over with a bit of paint on the edges and the filler bunged in. Over time the cut metal oxidises and tinworm gets a hold. My filler cap is installed in the plastic diffuser of my bumper. You may also want to consider the aesthetics of the filler cap location, as they can tend to look like big zits on the arse end of the car...

Always leave the petrol tank at least 1/4 full. Most fuel pumps sit inside the the tank and rely on the petrol for lubrication and to protect the pump from corrosion. If you let the petrol tank sit almost on empty you'll risk ending up with a seized pump.

The LED LPG tank fuel gauges are notoriously inaccurate. Get to know what mileage your car can do on a full tank both on motorway and A/B roads and use your experience to tell you when to expect the need to fill up.

LPG tanks do NOT hold their full capacity of gas. For example, a 50 litre tank will usually take about 40 litres before the pressure valve cuts off any further LPG. If any installer offers to or talks about bending the float to allow you to get that little bit more into the tank then walk away. Doing that is a criminal offence and an installer will serve prison time if caught. The 80% fill capacity is a safety issue. These tanks hold a very high pressure and 80% allows for impacts, temperature variations, etc. without compromising safety. Exceeding that could cost you and others your lives.

Filling up - LPG stinks of a mix of piss and fish. It's not nice. You'll find that out because whenever you fill up you get a momentary jet of it on your hand when you uncouple. Lol. Nothing you can do about it so just get use to your wrist smelling like an unhygienic incontinent old lady It's also worth getting the LPG installer or a friendly LPG user to show you how to use the filling pump equipment if you don't already know. It's a tad more involved than just whacking petrol into your car but it's not complicated.

All in all my experience of LPG has been positive. I bought my '03 plate E46 330ci 2 years ago with 80k on the clock and it had been LPG converted from very early on in its life (at around 18,000 miles). LPG leaves very little crap in your engine so the exhausts were cleaner than any other 10 year old car I've ever seen. It also means that I've never felt the need to use an engine flush or Terraclean treatment. I've covered 30,000 miles since buying the car and other than it needing a replacement vaporizer when I bought it (which was about £400 IIRC and the garage ended up paying for) it's been trouble-free (touch wood). LPG engines DO use petrol when they fire up and until they get up to temperature, so you will still need to refill the petrol tank from time to time. I generally fill it to half a tank and wait until it gets to 1/4 then put another 1/4 in. It takes aaaaages to do that though so I pretty much discount the cost of petrol in my running costs.

Based on the consumption of my 3.0 Beemer, 30,000 miles on petrol would've cost me about £6,400. On LPG it'll have cost me about £3,745. In a diesel doing about 50mpg that would've cost me about £3,620, so on a par pretty much with the LPG cost. The bonus of being a petrol engine rather than a diesel engine is that there's no expensive turbo, high-pressure diesel fuel system, exhaust gas recirc valve, complicated diaphragms and pressure sensors etc to go wrong. It's also a hell of a lot cleaner for the engine AND the environment than either petrol or diesel. And of course (in my situation anyway) I get the poke of a 3.0 litre petrol 6 cylinder that gives much bigger smiles than thrashing a rattly 2.0 diesel 4-pot

You have to declare your vehicle as having a modification, but most insurers are generally ok with LPG. Yep in most installations you lose the spare wheel well. You can either sling a spacesaver in the boot or do what I did and just have a can of Tyreweld in the boot, ditch the spare tyre altogether and have breakdown recovery too (just in case).

 

No worries mate. I'll probably have an LPG kit fitted to my next car too, am that happy with it

 

out of interest, what sort of cost are you looking at to get it installed?

 

Good question. If memory serves, to supply and fit a decent new sequential LPG system to a 6 cylinder engine you're looking at £1,400-£1,800.

It made sense because the petrol cars are generally cheaper than their diesel counterparts for most car marques.

Example (assuming we just take the quoted mpg figures as true, even though we all know you can knock 10% or so off them) - say you want a BMW 3 series coupe M-sport. No more than 10 years old (so 2004 onwards) and max 90k on the clock.

2004 2.0 diesel - £4,500. 0-60 in 8.8 seconds, average 49.6mpg.
2004 3.0 diesel - £6,500. 0-60 in 7.2 seconds, average 42.8mpg.
2004 3.0 PETROL - £4,900. 0-60 in 6.5 seconds, average 31mpg (converts to LPG equivalent of around 59mpg).

Add the cost of the LPG conversion to the petrol car and you're paying roughly the same as the cost of a diesel 3 litre. The petrol car is faster, gets better MPG and has a simpler engine so less horrors to go wrong... Plus the longer you own the car and the more miles you cover, the more you save. Yep you could get the 2.0 diesel but then you could buy a 320 coupe (2.2 petrol) and do the conversion on that. The price difference is roughly the same so the maths stacks up in favour of an LPG 320 over a diesel 320. Personally I fail to see the logic in going for a 2.0 petrol when they get the same MPG as the 3.0 near as damnit.