Converting to LPG

[Ryan1980]

Hi All,

I am considering converting my 1974 450SE to run on LPG. Currently i am getting around 400km's from a tank, i believe the tank is 90L . So economy is very bad. I would love to be able to drive my 116 more!

The government gives you $3000 to convert here in perth ($2000 federal, $1000 state) so i only have to pay anything over $3000.

Has anyone converted their 450? Just after people's opinions. I've heard various things , such as it wears out your injector's and valve's quicker.

Also can anyone reccomend a place to get it done?

Thanks

Ryan

[OzBenzHead]

Ryan:

1.  How about a tune-up first?  Many 450 owners claim their fuel consumption to be not much higher than that of a 280.  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).

2.  Many LPG proponents recommend going gas-only - not dual-fuel.  With dual-fuel, and an "old-fashioned" ignition system such as in the 116, you'll only ever have your ignition set optimally for one fuel or the other; the fuel for which it is not optimised is likely to give you terrible performance in all respects.

3.  If you decide to go LPG, be sure you find someone who specialises in doing the conversion on older Benzes; your average Holdon and Fraud corner-servo LPG convertor likely won't have a clue and you'll get a bodged job.

4.  From what I've read in the past - here and on the Ozbenz forum - a proper LPG conversion job on something like a 116 is likely to cost you about $5K, so you'll still be handing over at least $2K of your own money.  Unless you do extensive distances in the car while you own it, you might never save a cent.

5.  The federal government intends to tax LPG sometime in the next couple of years (2010?), so then there will be little, if any, advantage in converting to gas.

Just my 2 cents' worth.

[WGB]

An LPG conversion sounds good and appears to make good sense until you live with it.
I owned a Dual Fuel Landcruiser that had all the gizmo's like Automatic Petrol start (Starts easier and keeps the injectors working a little), Dual advance curve ignition, automatic valve lube system and also owned two other petrol only Landcruisers.

The consumption on LPG was around 10 mpg while Petrol was 14 MPG vs 16 MPG overall for a normal-petrol Landcruiser in my hands.

Wear on Vaves was measurable over a 60,000 km span and I subsequently sold the vehicle because of this factor - but really it needed Stainless steel valves.

If you want any further info try "Wheels" magazine or suchlike and compare the fuel consumption for a petrol and LPG Falcon - it reads significantly higher and this is with a manufacturer doing his best.

As you can see I am very off the idea until they make specific motors with high compressions that better suit the stuff.

Bill

[Ryan1980]

well i guess i should look into why my fuel consumption is so bad... if 400km's per tank isnt the norm. I certainly hope it isnt!
The car does seem to be running very well though...I suppose this doesnt neccesarily mean it doesnt need a tune up?

Is this something most mechanics would be able to do, or should i be looking for a mercedes specialist?

I wonder if the mercedes valves would handle the LPG - ive heard they are hardened valves.

[13B]

400km/tank is what I get from my 6.9 

BUT

when Road & Track reviewed the 450SE/SEL in '73 and the 6.9 in '76 they found both returned the same 13mpg (average) for equivalent driving.  On the 6.9 its put down to the 2.65:1 diff. 

I did some freeway driving and found I got an extra 50km to the tank, so constant speeds at 100 or thereabouts will net better distance per tank.

Sucks to be me and (by the sounds of it) you, because most of my driving is in Melbourne traffic where getting to do more than 60km/h is as rare as being able to do a constant speed for any distance.

Moral here: don't expect miraculous improvements on 400km/tank

Now to LPG, my infamous red 1977 450SE in the 90s was converted to LPG at around 1/2 million km and went on to just over 1 million km on gas before it just died due to lack of compression.  I didn't think at the time to disassemble the engine and see what damage was done.  That car was dual fuel but to be honest I never ran it on petrol after the conversion and adjusted the tuning to be optimised for LPG.  LPG back then cost 16.5 c/litre and it was still possible to do interstate cruising at elevated speeds (140-150km/h seemed to suit it fine).

I.

[SELfor50]

well i guess i should look into why my fuel consumption is so bad... if 400km's per tank isnt the norm. I certainly hope it isnt!
The car does seem to be running very well though...I suppose this doesnt neccesarily mean it doesnt need a tune up?

Is this something most mechanics would be able to do, or should i be looking for a mercedes specialist?

I wonder if the mercedes valves would handle the LPG - ive heard they are hardened valves.

Ryan, for the last 6 months i've gotten pretty much right on 400km a tank.
Most I had gotten was about 440, and half of that was highway cruising and I ran it till it ran out! (carried a jerry can of course)

In the last week since I did the major service (Oil / Filter, Fuel Filter, Transmission, Exhaust tightening, Spark Plugs, Timing) I actually got 450km's from the first full tank after that (city driving) and didn't run it dry, still had some left.

However, when the car was on the hoist I noticed that the fuel pickup line from the bottom of the tank that runs to the fuel pump (i think) had actually kinked - almost completely kinked so to cutoff the supply.

I'm sure the increase in fuel efficiency is partly due to the service and partly to not making the fuel line so restrictive?! (I'd assume the pump sucks it hard if it's being restricted?)

The timing was wound back to 0 degrees.  I haven't yet re-adjusted the air/fuel mixture so it's still running a little rich from when i advanced the timing....but i'd expect the fuel consumption to increase a little more after i've done that.

A good solid service and checking these things (in my minimal experience anyway) should increase your fuel cons.

THE MAIN cause of bad fuel consumption though, for me anyway, is a Man's Right Foot!!   

[Martin 280s]

OBH, Funny you should mention this "The federal government intends to tax LPG sometime in the next couple of years (2010?), so then there will be little, if any, advantage in converting to gas." The government intends to do the same thing over here. There are a couple of good reasons! One is the natural gas used here, domestic and for vehicles, comes from Hugo Chavez' Venezuela and the other is a lot of folks converted their cars so now the Gov can tax a captive audience as much as they like!

[OzBenzHead]

[...] a lot of folks converted their cars so now the Gov and tax a captive audience as much as they like!

Yep.  I saw it coming in Oz and refused to be suckered (this time around).  Governments are such cynical bastards.   

Years ago, when LPG conversions became available in Oz (the early '70s), I had a car converted.  The power output was abysmal, the car needed constant re-tuning and still ran unhappily, and it developed a tendency to overheat.

Over a period of five years, when that car - a 3-litre P5 Rover - was my main drive, I recouped via the price difference between gas and petrol about one third of the conversion cost.

Never again. 

[Ryan1980]

Thanks for your opinions guys.

I guess the main thing im concerned about , is whether it will do any damage mechanically... i.e. will it damage the valves/seats , will it damage the injectors, and will it do any harm to anything else.

Today i got quited $3200 to do the installation over the phone...meaning i will only have to pay $200.

They tell me that with the valvesaver fluid they use, there shouldnt be any problems.

I'll give it a go if im satisfied it wont do any harm...

[peterq]

I know a couple of LPG installers (in the country, not in Perth) and their view is that a gas-only set up is better than dual fuel, and that modern electronic gas injection systems are much better than the old systems (described as fork lift truck systems by somebody on another forum).
If your 450 is a D-Jet it may get better results than a K-Jet as they can piggy back their electronics on existing systems.
On my 6.9 the big problem is finding space for the gas unit under the bonnet, so that's on hold while the installer does some research. This installer has a Ford Falcon XY GT-type ute on gas that he uses as a test bed for different tuning methods.

[oscar]

Now to LPG, my infamous red 1977 450SE in the 90s was converted to LPG at around 1/2 million km and went on to just over 1 million km on gas before it just died due to lack of compression.  I didn't think at the time to disassemble the engine and see what damage was done.  That car was dual fuel but to be honest I never ran it on petrol after the conversion and adjusted the tuning to be optimised for LPG.  LPG back then cost 16.5 c/litre and it was still possible to do interstate cruising at elevated speeds (140-150km/h seemed to suit it fine).

13B, I didn't realise you did that mileage on the 450.  Amazing.  You've probably mentioned it before but I missed it. 

Was most of those LPG km's done at those higher speeds you speak of?  Was there any rebuilds along the way?  Shame about no teardown afterwards. It'd be interesting to know if compression lost was cylinder/ring related or upper cylinder and valves or both but if it did 1mill all up without new rings or valves that's fantastic.

[13B]

I attribute it to the harder valves in the K-Jet M117 engines, the Penrite HPR-Gas engine oil, and long consistent high speeds which the car was designed to run at.  Other than that normal servicing... spark plugs every 50,000, leads every 100,000, oil top-up every week or two.

The car was also driven normally, no full throttle take offs or other stuff...

[Ryan1980]

would a 1974 D-JET m117 have the same hardened valves/seats as the k-jet?

[oscar]

That's a real toughie ryan.  I haven't found one official comment to say they do.  I mean, I've heard comments like all post ww2 mercs had hardened valves and seats for instance, yet a few times on this forum and the MBCNSW forum, the official line regarding upper head lubricant additives and unleaded fuel use for example, will stop short of including pre 76 w116 V8's.  Not only did k-jet come in after that but so did hydraulic tappets. 

In a way I reckon MB just cover themselves by not saying "we're not 100% sure, but she'll be right".  In the end I don't know one way or the other.  There's just stories like my 350 that is nearing 400,000km and has done nearly half of that on cheaper 91 RON unleaded without additives.  But like someone suggested earlier, some kits in other cars I've seen also have a valvesaver reservoir under the bonnet.

[bb]

The LPG itself does not bugger up an engine, a poorly installed conversion kit does. As far as I'm concerned, all else being equal, an engine will last much longer running on gas because it burns so much cleaner.

If the numbers stack up to make a good financial case to convert your 116, I would do it.