With the price of gasoline and insurance skyrocketing today, you might want to consider doing a do-it-yourself LPG project like this one.  Often, when a person picks a car, they don't often consider the operating costs (fuel, insurance, maintenance, depreciation, etc.).  As an example of a vehicle cheap to own and maintain, let's look at a used General Motors full-size (B-body) car.  They are durable (see how many are still being used in taxi service) and they are still plentiful and cheap in the used car market.  Besides, replacement parts are readily available and are dirt cheap.  These cars are also easy to repair by any backyard mechanic.  With it being large, utilitarian, and not new, these cars are about as cheap to insure as you can get.  An added benefit is that, at least in Ontario, cars older than 20 years are not required to be emission tested.  Other manufacturers' full-size cars would be similar.  Of course, you will still need to visit a mechanic who can certify that your DIY conversion meets provincial or state safety standards.  This certification will allow you to fill your vehicle with fuel.  Do NOT drive the car until has been certified to be properly converted.

Now these cars don't seem to be very fuel-efficient running on gasoline but are actually similar to modern minivans.  They carry a family of four comfortably and have enough trunk room to carry plenty of stuff.  Obviously, minivans can carry a more due to their blobbier design but we are looking to save money.  If you have to do any towing, full-size rear-wheel drive cars are a better choice than most minivans.  For this example, let's look at how we can convert a 1977 Pontiac Parisienne (Bonneville in the USA) to straight propane.  The car in this project was already converted to propane years ago but is a good example of what components are required and how they are installed.  Luckily, General Motors provided this car with a Chevrolet 350 engine, which makes replacement engine parts even cheaper and more readily available.  Dual fuel is another option but, since for this example we live in an urban area with readily available refueling stations, we will replace the gasoline tank to maintain our trunk space and optimize our conversion for maximum fuel efficiency.

You will need the following major components for this conversion:

The easiest and cheapest way to get these components is to scour the junkyards for a complete vehicle.  Since junkyards don't often get calls for these parts, you can get everything you need for $100 to $200.  If the donor car was from a northern area, the fuel line fittings may be corroded which will mean you will need to buy new ones.  You will need to check the tank for the expiry date.  If the tank has expired, you will need to have it recertified which could may or may not be cheaper than buying a new tank.  Your chances are much better obviously if the tank is in good condition and not too rusty.

You will need to check with your certifying authority if your planned conversion will meet their requirements.  Newer vehicles may require a electronically controlled feedback system to pass local emission requirements.

If you can't find a suitable donor car, the other option you have is to buy new parts:

DIY propane conversion kits are not generally readily available for most cars.  LPG is a very common conversion in Europe so newer European cars would be the most likely vehicles for which to find a DIY kit.  Other gaseous fuel suppliers may be able to put a kit together for you but this would probably done on a case by case basis.  I may start putting kits together for propane conversions some time in the future depending upon the feedback I receive.

There are not many automobile tank manufacturers and we are aware of two:  Manchester and Sleegers.  Sleegers has tank drawings available on-line you can use to determine which would fit best.  They also ship direct to the customer and have a tank recertification service.  Manchester will give you a recommendation after you send them the particulars of the application.

You will have to fabricate some brackets to mount the tank to the vehicle if the donor car is different from your project car.  You will also need to remove the gas tank if you are placing the propane tank in its position.  The tank should be securely mounted to the car so that it cannot come loose in the event of a collision.  The tank must be secured to the frame with high strength bolts.  The mounted fuel tank must have adequate ground clearance or you will end up scraping it or (worse) bumping it on the ground.  A good way to determine whether your tank will have adequate clearance is to first draw an imaginary line between the place where the rear tire meets the ground and the bottom of the lowest part of the back of the car (usually the rear bumper).  If all parts of the new fuel tank fit above this line, your tank installation will be OK.  If not, you will either have to look for a different tank or move the bottom of the the lowest part of the back of the car even lower.  This lowering could be done with a new class III trailer hitch but you will need to check with your certifying mechanic.

Since the tank is the most expensive part of the installation, it would not hurt to protect your investment with rust-preventative coating.  Do this after you have done the trial fitting and just before you are about to make the final installation.  Brand new tanks will usually have a fresh coat of white paint from the factory but you can still improve upon the finish with an additional coating of rust-inhibitor paint or rubberized stone-guard.  The white color is to reduce the adsorption of solar heat and is completely unnecessary for an under-car tank. 

To design the brackets, you will need to trial-fit the tank to the car and this will be much easier if you put the entire car up on blocks.  The car should be as close to level as you can make it and only high enough for you to easily work under the car.  Put the tank on a board and then place the tank and the board on a floor jack.  You may need to use leveling blocks if you are using a manifolded tank with different cylinder diameters.  Lift the tank into position with the jack.  The brackets you need to fabricate will securely connect the tank to the car so use cardboard as a template for your design.  Once you have a design that will securely connect the tank to the car, go to a machine shop and have it fabricated.

Bolt the brackets onto the tank and again fit the tank to the car.  Mark the frame rails with the location of the new brackets' bolt holes.  Remove the tank and drill the holes.  Finally, put the tank back in position and install high strength bolts long enough to pass through the brackets and the frame rail with enough thread showing to install a washer and a nut.  The new brackets will probably not meet the frame rails so you will have to use  washers to take up the clearance between the bracket and the frame rail.  Use the same number of washers on each side of the tank if possible.

If you decide to go with a trunk-mounted tank, you must have a way to sealing off any leakage from the fittings to the interior of the car.  Trunk-mounted tanks normally are equipped with an enclosure to contain any leakage and direct it outside of the car.  It is possible to retrofit a tank with an enclosure but this may require a recertification, which could add considerably to the cost.  I did do such a thing to a trunk-mounted tank and this turned out quite well.  Sleegers Engineering did this work and this tank will be used in Project 2 (look for this later).

If you find this project interesting and you would be interested in doing something similar, please visit the Raso Enterprises Alternative Energy Systems Forum.  You can find other like-minded people there who can answer your questions and give you good advice.

Send mail to fraso AT mergetel.com with questions or comments about this web site.
Last modified: November 12, 2004