Converting to LPG

[CraigS]

Seats, but not the valves.

[scraf]

I halved my fuel costs converting my 450 to LPG the other rmonth.

Although the "boy racer" in me has matured a little, I cruise now at 120 kmh instead of 160 kmh, ahem, mostly. The price here of LPG is about a third or maybe 40% of the price of premium petrol though, I believe LPG is slightly more expensive in Oz.

I am expecting to have to renew the valve seats on both heads in a couple of years, but that would be a nice time to do recon replacing the timing chain etc.

Installation with Polish parts cost me €1000, "Flashlube" an extra €65. I asked about backfiring, seems there is some sort of backfire protection built into the installation.

I'm happy I did it, I couldn't justify spending €100 to drive 400 km in a Mercedes, however I can justify spending €50 to ride in style for that distance. I drive a lot, btw, did a 650km return commute the other night, totally knackered on the home run, but enjoyed it none the less.

[Jaycee]

I got my 280 when it had done 200k. I don't think that the engine had been that well maintained up till then. I had an LPG conversion done by a shop in Sunshine, Melbourne that specialised in MB for $2000 (1993) I drove it up and down to Melbourne (150kl pr. day) until it had 450k up and was starting to puff a bit. I then had the engine rebuilt. A couple of the valves were throwaways, most would have been reusable but I got all new. The valve guides was the area where the most wear was evident. The rest of the engine was just normal wear but I did get 60 thou over pistons .  I have driven it another 170k. All these kls were done without the benefit of a flash-lube kit. I ended up getting a kit not long ago.

I get 6 kl to a litre of gas. I'm not sure what I get on petrol as I rarely use it and I've had a little play with the map sensor (and I'm going to have to have another little play with it one day .) The power is down a bit but with the 280 SE being a bit of a slug anyway it's no big deal to me. I trial and error the ign. timeing 'till it stops pinging on petrol.(About 4-5 degrees advanced),and I run NKG BP6EY plugs. I could hardly believe the difference these plugs made to the way the car ran. So much smoother idle and it seems to have a tiny bit more power and better economy.

This conversion used the old technology, did someone call it "fork lift LPG"? I'm sure today's conversions would give much better economy and power. I would do the same thing again. I am going to see about the cost of getting my 300 E converted.

[editjunk]

My 280SE - driven relatively hard and fast (I'm certainly no "granny"!) - returns 800+ km per tank (and, on a recent trip to Sydney - 800 km - with a boot full of tools and two persons on board, I got 900 km before filling up - just as the reserve light came on).

OBH, I know you to be a gentleman of impeccable honour & so would not dare to doubt your claim of 800+ km a tank from your car. However,  I was getting 350 km per tank city driving with my 350SE, which I thought was terrible. After consulting the forum (where most members concurred that this was about what I should be getting) & hassling my mechanic to tune the car "right", I finally accepted that a car built in 1973, weighing over 2 tonnes, with a V8 up front & a fairly erm... eager driver at the wheel, was not going to do much better. Would it be possible that your 800 kms are achieved on 100% freeway driving, going downhill with a tail wind stuck in the gap between two 18 wheelers?

I teetered on the edge of LPG coonversion indecision when I had my 116. I really wanted to save money, but was scared to damage the car, hesitant about making changes that may affect resale value, untrustworthy of gas conversion mechanics who had cut their teeth on Fords & Holdens. If I still had the car, especially if there were a $3000 rebate, I'd do it. Let's face it, a decent W116 can be picked up for as little as $1000 these days, even less if you're lucky. So if the conversion ruins your car, just pick up a new one. This may sound a little cavalier, but there's so much fog around this issue, I think it'd be worth it just to see once & for all about the hardened valves & engine wear.

[scraf]

Where I come from the bodies die, not the motors.

[OzBenzHead]

[...] Would it be possible that your 800 kms are achieved on 100% freeway driving, going downhill with a tail wind stuck in the gap between two 18 wheelers? [...]

Certainly those are my highway consumption figures, not town.  On the open road, using the speed limits as set minima, my M110 drinks 10.5 litres per 100 km, 11 (which is what it's supposed to do) at worst - say when there's a headwind or heavy weather.  A couple of years ago, on a super-fast trip to Melbourne via the inland roads - 2,000 km - when I cruised at highly illegal speeds and encountered nothing but B-doubles and locusts, I managed to use 13 l / 100 km.

When I want to overtake - or otherwise require a power surge - I use the stick rather than the kickdown switch.

Stop-start around town consumption is more like 15 l / 100 km.

There is a "Fuelstar" Link fuel catalyst inline device fitted (was there when I acquired the car) that supposedly is beneficial to fuel consumption and helps the car to digest unleaded.  Although usually sceptical of such devices, as it has never caused any problems I've left it there.  I've no idea what - if any - effect it has on my car's performance or consumption, but I'm not complaining.

The car now has 300,000 km up.  It is serviced, religiously, every 5,000 km (1,000 km sooner than the recommended interval); I use only good quality consumables - including brand-name-only 98 RON fuel (normally Caltex Vortex 98), and run my tyres at 36 psi (unladen) and 38 psi laden / on long highway runs.

By contrast, my M130 W108 280SE drinks a good 15%-20% more than the M110 under similar conditions.

[BAR]

I wuld be amazed to find any LPG conversion where the car or van returns better fuel consumption and for that matter power.

Read any comparison done by motoring press [Wheels / Motor in Australia] or even the stated figures for Ford or Holden on their factory built LPG models.

Where one wins is in utlimate running cost, where LPG is significantly less to buy than Petrol.

At $1.50 per litre for ULP vs say $0.75 for LPG your $3,000 buys 2,000 litres of ULP.  Even with your range of 400Kms per 90 litre tankful.. well that's 22 refills roughly.  Given that you know how many times you refill, well then work out how many years it would take to pay it off.

Now if you spent a few hundred dollars tuning the engine, then you should get abut 500Kms per tankful.

Also consider that you will lose most of your boot space and have the body work affected by the installation of the filler cap for gas, then decide if you should gas and go or just gULP gown the fuel and pay the bills.

[SELfor50]

Well sad BAR.  Every time I see your name I think of BAR Honda.... anyway.

Just on the fuel consumption...it's been raining here a fair bit recently.
Anyone else notice that there fuel consumption gets really bad all of a sudden when it's wet?
If it rains for 3days i only get about 300km's to a tank..  Can't figure out why. 

[Andrew280SEL]

If it rains for 3days i only get about 300km's to a tank..  Can't figure out why. 

Is it all that extra time you spend shredding spinning your tires?

[johnnyw116]

mercedes needs hardend valves and seats , LPG gives a hotter combustion and LPG has a low octane
value that is not optimal for your engine , you also must drive regular on petrol otherwise it does your carburator or injectors etc etc no good , they dont operate smoothly annymore when you only drive on LPG and in an emergency were you must switch over to petrol it would be nice that it operates properly             

regards : johnny  .                                   

[craigb]

I feel like we have had this conversation before but it is interesting to read all the different opinions and ideas. My feeling is that there is more difference due to state of tune, condition etc. and quality of conversions than in the fuels themselves so a lot of experiences are not necessarily 'apples with apples'.

I have had a good lpg experience on an old worn relatively worthless benz. I didn't worry about the condition or effects on the old worn carb - I haven't run out of petrol for 20 or so years because I am flush enough with funds now to fill when I get to quarter tank or so, so I don't run out of lpg either and therefore never ran on petrol. The car never went anywhere where supply of lpg was a problem. If this isn't the case for you then you really need to consider the usefull comments made by others.

LPG is actually higher octane (100? 110? or something like that) but it has a lower calorific (or a word something like that - see you can tell I am an expert!) value, so yes, litre for litre there is more 'energy' in petrol and should produce more power - but you can adjust timing and compression and not ping on the lpg. So I reckon BAR is right about new cars, tuned properly for straight lpg v petrol, but how much is the difference in these circumstances? I reckon you would need a stop watch to tell.

I am not sure it runs hotter (because it has less 'energy' in it) but mine never overheated so even if it does run hotter if your cooling system is in good shape it isnt a prob. I found and heard from others that the condition of your ignition system is really important and a dual fuel car will run crap on lpg and fine on petrol just because of dodgy lead etc.

Anyway horses and courses and all that and great we can all choose whatever we want but still good to share ideas and experiences. I love a car being just as the maker had it, nice condition and in good tune and you can travel back in time in effect as to how it was. I have my original cars but the lpg was a cheap handy runabout. I think my earlier comments have always been basically that I think it is possible to have a good running lpg car but most important is to get a good conversion by someone who knows what they are doing with the specific model it is fitted to.

[Ryan1980]

Thanks for all your opinions guys.

I've been to a couple of LPG places and although a lot of them have no idea what they are doing on the merc's , i managed to find a guy who sounds like he knows what he's doing, is honest and resonably priced. So i'm keen to go ahead with it.

The decision i have to make is whether to go dual fuel or dedicated gas.

duel fuel apparently has less chance of backfiring as it starts on fuel (Although the guy says it shouldnt backfire anyway, and if it does it wont do any damage on this engine).

dual fuel means i have to put a gas tank somewhere in the boot, perhaps where the spare tyre is... and maybe i could carry one of those tyre inflater/fixer things around. With straight LPG i could replace the existing fuel tank.

Obviously my injectors etc would eventually wear out if they aernt used on straight LPG, i guess thats something else to consider.

Any ideas/opinions?

Ryan