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LPG Conversion

Mod Details
PremiumNo Difficulty Mod ID1305 Creditevilution For450 Fortwo451 Fortwo452 Roadster453 Fortwo/Forfour454 Forfour Link Copy to Clipboard

LPG, The Money Saver

Wrong. Maybe in the good old days but not so much any more.

Why Not?

2 reasons.

Firstly, the cost of LPG has increased. Originally it was 30p a litre. Now it's about 60p and increasing (2018).
If you take into account that LPG is 25% less efficient than petrol, it's equivalent to paying 80p a litre for LPG.

LPG is 45% less efficient than diesel, an equivalent of paying 90p a litre for LPG.

Because the savings have been drastically reduced it takes much longer to recoup the cost of the conversion.

Secondly, people generally want everything cheap which is what blindly leads them to LPG in the 1st place.
Companies know this and over the years, cheaper and cheaper kits have been released.
They are cheaper because of lower quality construction and missing out on vital features.

What Vital Features?

The main lost feature that was present in 1st generation kits and expensive modern kits is a lubricator.
Cheap kit manufacturers realised that engines would last long enough to get the kit out of warranty.
These kits were also much easier to fit, took less time and took up less space.

Smart And The Lack Of Space

The main thing about smarts is that they are small. Enough room to be fairly practical
but not enough that you want to waste space lugging around extra shit in your boot.

There are 3 main types of LPG tank.
Custom, toroidal and cylinder.

The custom tanks that replace the under-floor fuel tank are ridiculously expensive.
Toroidal tanks are designed to go where the spare wheel usually goes. No such thing on a smart.
So you have to use a cylindrical tank in the boot which is a massive waste of space.

Woah, Backtrack. Lubricator?

Yes. Petrol and diesel actually contains additives including lubricants.
This helps reduce valve and seat recession. LPG is pure vapour with no lubricating properties.

This means that valve and valve seats wear much quicker in an LPG converted engine.

So, to counteract this lack of lubrication, an external oil tank is fitted to inject oil into the cylinders.
However, only expensive kits have a lubricator but expensive kits are expensive.

If you take into account the expense of the kit and the small savings of using LPG,
You'll have to do about 60,000 miles to break even on an expensive kit.
Even on a cheap kit, you'll have to do 40,000 miles to break even.

However, the smart engine probably won't reach 40,000 miles on a cheap kit.
So, if you factor in a replacement engine or head, it's not worth the conversion.

So, Add A Lubricator And It'll Be OK?


Petrol and diesel actually help cool the engine as well. We already know that expanding gases cool down.
LPG has already expanded by the time it reaches the engine so it doesn't help with engine cooling.

So, LPG engines run hotter. This can affect the engine head and possibly even the head gasket.

Excessive heat kills engines, even more so on aluminium engines that already run hot.

Are There Any Benefits?

Yes. If you buy the car with it already fitted, do a lot of miles, have a local fuel station that has LPG,
the car has the lubricator injector system already fitted and you don't need boot space…


You'll save money every time you fill the car.


AMR Autos