Thread: More Km for BP Auto gas

There is, but a lot is variable and not neccessarilly particular retailer orientated. It depends on the mix of lpg (butane/propane from memory). My FIL was Kleenheat Gas manager for years and he did tell me the mix was a primary reason and mixes could vary dramatically. The mix can depend on what they have available, hence why there is some variance in performance and economy.
I have had 3 lpg vehicles and the variance in general could be up to 10% economy and power. We also found that when we drove to SA as soon as we hit servos supplied by SA the fuel economy improved by 20% eg Pajero would go from 400kms per tank to 500kms per tank every time and the opposite coming back and we had done this a few times to verify. RR would go from 500kms to 600kms per tank (100 litre).
It can also do with when you fill up to. If you fill up on a really hot day you actually get less for your money as lpg expands and when it contracts you can lose around 5-10% volume. I know with the RR if I normally filled the main tank from empty run dry, I would get 100litres in on a normal day/same on a hot day, but would lose economy on the hot day fill. If I filled up on a real cold morning at 0445 going to work I could sometimes squezze in 105 litres and even if it was only 100 litres would get much better economy. I would only fill like this before a drive as if filled on a cold morning and not driven and left in the sun the lpg can expand and vent. I learnt not to do this very quickly.
The same is actually true to petrol and diesel as well but to only a very minor degree due to molecular reactions with cold and heat extremes.
Hope this helps.

CraigE , I concurr with most of what you say , but arent overly convinced that the SA LPG is that much better , Everything you say about the "Cold" fillings is spot as can be expected by the blends Vapour pressure ,which is dictated by Ambient temperature. The interesting part is usually the debate over the Butane to propane Mix ratios. Some think that the more propane in the mix the better the power . Alas ,from my Drag racing experiences .I found the opposite to be True . The More butane the better !!! . Its a tradeoff between the Octane level in Propane (being 10 points higher than Butane) and the Calorific value or BTU's of Butane , some 20% greater BTU's in butane than Propane. So while Propane has less propensity to Knock (ping , pink , Detonate . Diesel , pre-ignite etc )the butane has more bang for your buck , just careful control of the Spark/ignition timing and Butane allways workerd out better .

Removed - see full answer in my next post below.

Dont Know where your getting yours from either , Propane is C3H8 , Butane is C4H10
Youve got it badly wrong Isuzurover !! While your there, look up the Effect on VE between Propane and Butane and Petrol , look up the difference in Entropy ,
Have a look at this simple chart , remembering that the the LPG we use is a Vapour , so Comparisons by Volume are relevant , by weight are not !!

Originally Posted by 400HPONGAS

Dont Know where your getting yours from either , Propane is C3H8 , Butane is C4H10
Youve got it badly wrong Isuzurover !! While your there, look up the Effect on VE between Propane and Butane and Petrol , look up the difference in Entropy ,
Have a look at this simple chart , remembering that the the LPG we use is a Vapour , so Comparisons by Volume are relevant , by weight are not !!

OK - seems we are both correct - you will notice in the table you posted it gives Btu/lb - and Propane is slightly higher. But in terms of Btu/ft^3 - Butane is higher.

Originally Posted by black betty

How come I thought Auto gas was Auto gas?

Where I live Apco outlets consistently have gas as good as the best of the others and I would rate BP as one of the best, but it is slightly dearer.

The supermarket discount stuff is consistently the worst. Talking maybe 15% less k's per tank, sometimes a bit more.

In fact if I have a bit of Apco gas in the tank and fill with supermarket stuff then drive off I can actually feel the loss of power as the new stuff comes through the system.

cheers, DL

Actually I am pretty sure there are no standards applied to "autogas".
This is primarily a blend of Propane & Butane. Its currently around 50/50.
Its swings and roundabouts with regard to energy value between the two when you buy via a bowser ie the energy value of a 60/40 blend is much the same as a 50/50 blend. Before jumping at this comment,look at the weight difference between the butane & propane on the above chart.
CraigE You get charged for the energy value each time you fill with LPG, forget about litres. The weights & measures people check bowsers all the time.
Basic maths.
My 72 litre tank (@80%) can take between 68 & 76 litres when totally empty. The reason is I really take 72 litres every time but the bowser has a tempreature probe which factors in the volume variations due to expansion- or contraction which is supposed to be 1% for every 5 deg increase in product temp- not the atmosphere.
I used to drive a LPG tanker & laugh at the taxi drivers at the depots I filled, who went beserk at being charged for "more than their tank could hold" but quietly handed over thier cash when they thought they were short charged. I gave up explaining to the console operators.

The reason for mileage improvement? Some servos take 100% propane, cant say who, as its a moving target. Some vehicles run better on it as the overall octane rating is higher, but a vehicle tuned to autogas will run just as good.
Simple fact is until there are enforceable standards - there are at the refinery- there will be a wide range of LPG mix out there. If your car runs well on a particular brand ( Gogas is sold in house - not W.A) Mobil also is mostly internal that doesnt mean a 3rd party wont get called in to fill the Servo tank from time to time so there is no guarantee IMHO.