If your car is running on LPG and you want to save even more money you can run on propane from cylinder propane tanks sold for domestic use (heating, food cooking). In this article I will explain how to transfer LPG from cylinder tank to car LPG tank.
LPG or liquid propane gas is a mixture of propane and butane. Different proportions are used in countries from as low as 40% propane 60% butane to as high as pure 100% propane.
Why propane is better fuel than butane?
Firstly, propane boiling point is much lower than butane. Propane boils at -43.6°F (-42°C) while butane boils at 30.2°F (-1°C). Why it matters? In cold weather you need steady supply of gas to your engine or else it will stall. If you have open loop system LPG could actually backfire breaking your intake manifold or air filter box. Running on butane your LPG reducer can freeze instantly and cut the supply of gas. Some northern countries change the LPG proportion in the winter to help drivers avoid such problems. Usually from 40% propane 60% butane it switches to 60% propane 40% butane.
If you consider transferring LPG from domestic cylinder tanks you must know that gas composition is probably worse than what you get at the gas station. Hovewer in theory you can drive on pure butane as long as it is in gas form. But keep in mind that at freezing temperatures you will probably have many problems. If the air outside is for example –20C it would again liquify butane in the intake manifold even if the reducer supply butane in gas form.
What you need for LPG transfer?
This is the list of items you need for LPG transfer:
- Hose clamps;
- Pressure hose rated at least for 10 BAR or 145PSI;
- Used inline fuel pump (more on this below)
- Fittings for your LPG inlet and outlet ports
- Inline GAS filter
- Electrical wire
- Switch and clamps (optional)
Now more about the items from the list. Basic diagram for connecting all of this together is as follow: propane cylinder tank-> outlet adaptor fitting –> hose and clamp->infline gas filter->hose and clamp –>fuel pump-> hose and clamp-> inlet port fitting.
You can find hose for LPG online or at your local auto parts store. It must be suitable for pressure and liquid gas because while transferring there is quite a substancial pressure inside. Basically pressure is determined by LPG composition and outside temperature. Look at the diagram below.
For example, lets take 60/40 propane/butane mix and at 80F (or 26C) you can see that pressure is 86PSI. So your hose must be rated to support that.
Next comes fuel pump which will act as LPG pump. (Un)fortunatelly this is the most important part of the entire system. And not every fuel pump is suitable for the job. I can tell you that you should look for inline fuel pump that are rated for as high pressure as you can find. The one I am using is from old Renault Espace 2.8 liter gasoline engine.
Is it safe to use ordinary fuel pump as a LPG pump? Yes and no. This fuel pump is not rated for LPG and for this pressure but it has aluminum housing and all ports are also aluminum, so no plastic parts to break easily. Worst that can happen is the pump will seize inside but my setup actually lasts half a year and still works. The pump itself will cost you about 20$ or 15€ (that’s what I paid for it) but of course it depends on your local market. Try to use ebay if you can’t find anything nearby. The cheapest I could find online was about 90$ is a fuel pump for Renault Espace II 2.0i/2.1TD/2.2i/2.8i 91-96 EP2190 but you should really look at scrap yards instead.
For the fittings I can’t tell exact how to get these, but basically you just need to connect everything so that every part will hold the pressure. Cylinder tank fitting are usually easy to find and buy, the hardest part would be inlet port fitting to your car’s LPG gas tank. Aftermarket fittings are basically non existent because most of the people don’t transfer LPG from cylinder tanks to their cars themselves but you should look at the connection type on your car’s filler point and find lathe man to make custom fitting with threads on 1 side and nipple for hose on the other.
GAS filter is also very important because domestic cylinder LPG tanks are often very rusty and dirty inside and you must protect your fuel pump at all costs. It’s better to change or clean gas filter than to find another fuel pump. What I use is metal case gas filter which actually is sold as gas filter for gaseous stage. But again, metal casing is very strong and it should hold without any problem.
Electrical wires are optional. Operation of fuel pump is very simple. You connect ground (usually black cable) to battery negative and power to battery positive. While pump gets power it will operate non stop. Be sure to check correct inlet and outlet ports so you won’t accidentaly try to transfer LPG in reverse. You can install simple ON/OFF switch for easier control and operation but you could just connect wires directly to the battery ports.
Hose clamps help to keep everything together so tighten all parts really firm.
You can see how all system looks like in the photo below:
Connect everything like in the picture and slowly turn LPG cylinder tank valve open. At the same time be prepared to turn on fuel pump so it can start pumping easily. When not powered, the pump acts as a 1 way valve. If everything is connected well then you should hear the LPG flowing into your car’s LPG tank. Be carefull not to run the fuel pump dry. It’s best to use opaque hose and actually see the stream flowing. When cylinder tank gets empty the sound of pumping will suddenly change. You should immediatelly turn the pump off. Usually I can transfer 50 liter cylinder LPG tank in about 15 minutes running on car’s battery (12V). In theory this pump should work even faster when car is on (14V alternator).
To be safe, run this setup only in open area because if there is a leak, gas can quickly accumulate in your garage making dangerous situation. Also don’t smoke or have any open flames nearby.
Total cost and savings
In this economy running on LPG is the way to save money and running on domestic LPG you can save even more. The total price including fuel pump and fitting was about 40$ and it paid for itself only after 100 liters of LPG or about 2 domestic 50l tanks. I have BMW E38 730i and it consumes about 20l/100km but according to my calculations it is still cheaper driving this gas guzzler than runing on diesel.
Additional photos of the setup:
People selling these LPG transfer pump kits on Ebay get exorbitant prices like £400 or $500, you can DIY for less than $40. If you have any question, you can ask below.