LPG Discussion Forum

For the past month my average MPG readings from tank to tank have dropped from 16MPG to under 13MPG. It did exactly the same over the winter last year too.
I'm only running short (sub 5 mile) journeys so its not really getting a chance to get to full operating temperature, with the gauge just getting out of the cold zone by the time i'm shutting the engine off again.

Could it be just down to the drop in temperature (and therefore the amount of time it takes to warm the vehicles coolant up)?

As i understand it, the liquid LPG stured under pressure in the tank is turned into a gas by the heat of the water running through the reducer/vaporisor and its tapped into the heaters circuit would the fact i'm now using the heaters (so taking some of that heat away) make a difference or is it likely to something else?

One of my mates has the same vehicle but running an injected engine with SGIS and he's not noticed a drop at all.

I'm running a BiGas open loop single point system on a carb'd engine with only about 9000 miles use on it. Its still registering the same emissions as it always has so the system hasn't gone way out of tune.

It's open loop. There is no compensation for any climate or altitude effects.

So its just down to the cold then?

Looking forward to my engine conversion with SGIS then.

you will also no doubt be using your heater, lights etc, it all adds up.

john_d wrote:you will also no doubt be using your heater, lights etc, it all adds up.

Sorry to contradict you john-d. What engine is this? If you're getting 13 to the gallon, I'm guessing it is something pretty large. V8? If so it won't make a 3mpg difference having your lights, wipers etc. on. If it was a small engine then it make a bit more difference but not on a big torquey engine.

But your heater? Not sure about that one, as I'm not an expert in LPG vaporisers and what temperature they require to change the liquid to a gas.

sportston wrote:I'm not an expert in LPG vaporisers and what temperature they require to change the liquid to a gas.

anything above -44 degrees Centigrade. So that isn't significant unless you live above the Arctic circle.

It will be changing to gas, the problem is that the gas will be colder and therfore more dense. In multi point systems there are corrections for teh gas tempratue, a closed loop system will compensate from the lambda but open loop can not.

You might need to lean the mixture down a littel during the colder months.

classicswede wrote:It will be changing to gas, the problem is that the gas will be colder and therfore more dense. In multi point systems there are corrections for teh gas tempratue, a closed loop system will compensate from the lambda but open loop can not.
You might need to lean the mixture down a littel during the colder months.

Ah, that would explain it. Density factor. Thats another new thing I've learnt today.

All cars do a bit less in the cold

Its not a big torquey V8 engine unfortunately but a relatively underpowered 1.9WBX vw engine running a pierburg 2e3 twinchoke carb on open loop trying to push a 2 ton minibus around.
Vans manual says 20mpg urban on petrol so 16mpg is 20% loss. 13mpg is a 35% loss.

Never thought about gas density. It does appear to have more power when the cold weather sets in.

Zebedee wrote:Its not a big torquey V8 engine unfortunately but a relatively underpowered 1.9WBX vw engine running a pierburg 2e3 twinchoke carb on open loop trying to push a 2 ton minibus around.

Crumbs thats bad economy then.

It is but it also means that the extra load on the electrical system and hence the extra drag from the alternator, would have a greater effect. There's this poor little engine working it's socks off to drag a huge great, highly un-aerodynamic shed around and then it's expected to drive an alternator that is supplying power to run heater blowers, headlights, heated rear windows, wipers, etc as well. Not surprising it's using a lot of fuel really.

Gilbertd wrote:It is but it also means that the extra load on the electrical system and hence the extra drag from the alternator, would have a greater effect. There's this poor little engine working it's socks off to drag a huge great, highly un-aerodynamic shed around and then it's expected to drive an alternator that is supplying power to run heater blowers, headlights, heated rear windows, wipers, etc as well. Not surprising it's using a lot of fuel really.

I agree. In this case the engine is being worked pretty hard and the extra load of all the electrics may contribute to the problem. I take back what I said earlier as it is obviously not applicable in an engine this small and overworked.

petrol vans are never good on fuel mostly because of the stupid low axel ratio,s as they are originally designed for diseasal engines,this means they go like stink but are constantly revving their tits off.
My old sprinter 2.3 lpg only, used to give 3.5 miles per litre , empty, loaded, loaded with a loaded trailer,did,nt make any difference.

My cars mpg is getting better though now the weather is cold and damp,petrol consunmption is slightly worse due to the extra 500 yards or so before change over.



woody

Possibly doing less mpg in the cold as running richer due to more dense lpg coming out of reducer, but not necessarily.

Consider this also: Colder LPG is more dense, but so too is colder air. Colder air (for a set flow of LPG) would make the engine run leaner. True, the driver will compensate for the colder air by applying slightly less throttle because the engine will have better volumetric efficiency, but the colder air will have less velocity going through the mixer unit and this could affect the 'signal' that the reducer receives and therefore the amount of gas that is mixed with the air. The net effect of cold LPG and cold air could affect the mixture either way depending on the dynamics of the components and the calibration.

Generally, a slightly over-lean mixture will slightly improve economy but this effect drops away very quickly as the mixture goes leaner still. A too lean mixture (at this extent) will have a much worse effect on mpg than a too rich mixture. A 10% rich mixture won't use 10% more fuel, a 10% lean mixture might use more than 10% more fuel. The system would have to be very rich to cause the 20% loss in economy that you're finding, more than the temperature difference between winter and summer running could account for.

Besides the point previously raised (by others) about effects on fuel economy, another point that can affect them is driving habits. In the cold, driving habits can cause interpreted differences in fuel economy. If you only drive 5 mins to work but have the engine running for 5 mins before you set off to clear the windscreen etc, this could easily cause the economy to drop by more than you're saying. Driving slower, the engine may be in a different load range where the mixture of the LPG system isn't efficient, or the vehicle speed may be too low for the torque convertor to lock up in an automatic gearbox, an automatic gearbox probably won't lock the torque convertor anyway until the fluid warms up.

There are many more variables than just gas temperature!

Simon
www.Lpgc.co.uk
07816237240

Looks like i'm just stuck with it then for now.

I'm saving up the pennies and planning on an engine conversion next spring.
It will be going from a 78bhp 1.9 carb'd engine (the design of which hasn't changed since the early 80's) on single point open loop to a 115bhp 2.0 fuel injected engine running sequential gas injection. Been told by those in the know that have done the conversion before that a 10-15mpg increase is possible.

Why not do what they do in Sweden and fit a real engine....

Volvo B23

classicswede wrote:Why not do what they do in Sweden and fit a real engine....
Volvo B23

Hahhhaaaaaaaahahhhaaa.

You want a real engine, buy a Hayabusa.

Wanna fun engine, by an Alfa V6 or an Alfasud cloverleaf (but be prepared for the bills).

Super sexy engine, Ferrari (but be prepared for bankrupcy)

Wanna good all rounder, go japanese and 6 cylinder.

Wanna reliable but boring tank, buy a hideous Volvo. From the company that hasn't made one good looking car for the last 50 years, in fact they've made a point of progressively producing ugglier cars year after year. Yes they make tough engines, but its hard to own one of them without thinking about where you are going to get your next set of slippers to go with your new pipe and cloth cap and... "whoops there goes another one of those pesky pedestrians under my wheels. I wish they'd stop doing that, they make the road so bumpy! I nearly spilt my cup of tea. No Fido get back into the back seat. You naughty dog! Hmmm. What's that strange smell? Whoops I left the hand-brake on again...."

Please think carefully about this...The last thing this world needs is more volvo drivers. Keep death off the roads and crush a Volvo. Or invite a few bikers over for a ritual sacrifice of that most evil spawn of Satan, the Volvo Estate! You'll find no shortage of takers I guarantee it. In fact, I personally volunteer to supply the petrol to pour all over it. And the matches too.

That's a pretty stereotypical view, even if there may be a little truth in it. But, you have obviously never driven a Volvo V70R, that would change your views of Volvo estates forever. The V70 T5 is the one used by most police forces as a motorway pursuit car, for good reason, but the V70R is something else!

The V70R engine is quite weak and will not make massive power.

The classic 4 cylinder engine will make massive power with far less work.

And one of the fastest 4 cylinder drag cars is

http://www.youtube.com/watch?feature=pl ... kgGZqbgYYo