Thinking of sticking an LPG tank in the boot of the Merc. I do about 15K per year at 22-23mpg average hitting 24-26mpg on long motorway journeys. i recently filled up at a motorway service station and shoved over £120 in the tank which got me thinking about LPG.

Apart from £2K to fit it, are there any down sides? Long term engine wear etc?

Other than losing the spare wheel I am struggling to see any. Any recommendations for places near Southampton?

Cost goes up per cylinder, so on a V12, don’t expect it to be cheap. That said, you’ll get your money back after probably only 20k miles.

LPG works better on big lazy engines than small high revving ones, so can imagine your merc would be ideal. Speak to some convertors first though, check it’s on the application list. Many cars can’t be converted for various reasons!

My Dad had his astra converted at about 9000 miles & it is still running fine after over 200,000. He has only had minor problems easily repaired, the tank is a little small & LPG stations can be rare in some areas. I can’t think of any other issues, if the maths meant I would be better off I’d have it done. Future LPG prices against petrol is a gamble you will have to take though.

Tank size is the biggest problem. You can only fill them to 80%. MPG is 10% lower as the calorific value of gas is lower than petrol (unless you had a crap fuel injection system in the first place).

So… if you’re not careful you can end up with a 100 mile range.

Merc’s boot is reasonably big and only needs to take a couple of suitcases as I have the truck for the bikes and big stuff.

I understood that LPG had been fixed to 2014 which means I should get payback within that period.

Rubber – what ‘little’ problems? When the merc has a ‘little’ problem it still seems to cost £500 to drive past the garage.

We buy used petrol Mitsi Shogun wagons and have them converted to LPG and use them for the farm vets. Seem pretty reliable and the figures do make it worthwhile. Most important bit would finding somebody experienced to convert it.

Recommendations around Southampton?

I’d be interested in any recommendations around S’oton/Pompy too; wanting to get my Range Rover V8 done.

We have about 40 LPG vans here, some factory converted (Ford) some aftermarket. These vans have a harder than average life, problems happen when they breakdown as there are few garages that deal with lpg repairs and so are priced accordingly.

I thought the decreased duty on LPG was being dropped in 2012?

Main benefit for us is that LPG vehicles are exempt from London Congestion charge (for the moment).

Also be aware you cannot take an LPG vehicle through channel tunnel.

LPG is very common in Oz. Sis and BiL have there Land Cruiser converted and the only precaution they take is to run it on petrol for the first few miles as the gas burns ‘dry’ in the engine.

I had a Merc SE380 with an LPG tank in the boot.

Pluses – There was still plenty of room in the boot for kit bags. I used to put my bike on the back seat. It was very cheap to run. I paid £1500 for the conversion. I estimated that this would pay for itself in 2 years. Had the car about 5 years, then my brother had it for a couple of years. It was a great car for long distances.

Minuses – You had to start the car on petrol then switch to LPG when the engine warmed up. If you switched too soon you risked a blow-back through the carb’, this would sometimes be enough to blow one of the vacuum pipes off. You’d know this had happened because the engine would idle rough. It was a simple fix of taking the huge air filter off and pushing the pipe back on.

SB

The little problems I mentioned, I don’t know exactly what they were but something like a filter or similar meant the gas wasn’t kicking in so the car just continued to run on petrol. Fixing took less than 30 mins on the couple of occasions it happened.

People have mentioned starting on petrol then switching to gas. Dad’s car does this but it all happens automatically, the only reason I know what the car is running on is because there is a little light to tell me. His conversion is now very old and I would get one even if they haven’t improved in the last five years though I would expect they have.

Went LPG with a BMW 6 cyclinder.

Drives on petrol till warm enough (3 minutes) for LPG to kick in with a beep and light indicator.

Just check the LPG model is recognised by your insurance and you get a fitting certificate and can buy spare filters cheaply.

My garage offered free lifetime servicing etc £1500 cash…

I work at a pump filling cars at one of 2 places on the island, people are in regularly for the lpg, up to twice a week on normal driving and thats combined with petrol!