Solar Ricardo

Solar Ricardo

Sunday, October 2, 2011

Ridin’ w/ Sweet Lady Propane: A few notes about propane powered vehicles

by W. Joe Hoppe
photos by P.S. Monear

From OBSOLETE! Magazine #4

Here in Texas it’s pretty much a given that every family needs at least one pick-up truck. And everybody knows that old trucks are way cooler (and infinitely more affordable) than new ones. Even though there are lots of arguments for old cars and trucks being less damaging to the environment than newer vehicles, claims that re-use zeros out pollution over time, concern with the toxic chemicals, petrochemicals, and silicone in new cars, lead or other heavy metals in batteries, etc, there’s no denying that old trucks from the pre-catalytic converter days pump out a lot of hydrocarbons when you’re driving them around. So I’ve got to admit that driving around Austin in my ‘71 Dodge pick-up, even with its economical and bulletproof slant six engine (225 cubic inch displacement) made me feel like I was more of a problem than a solution in the fight against global warming.

Fortunately, there’s a lot of information out there on the interweb about converting your vehicle to propane. And even more fortunate for me, one of the country’s premiere gurus, Franz Hoffmann ( lives about 30 miles away in Bastrop, Texas. I also was able to access a lot of good advice through a website devoted specifically to slant six engines at

After some research, I decided to take the plunge and convert my truck whole hog, not to some system that would switch back and forth from gas to propane, but a deep commitment to Sweet Lady Propane, and only Sweet Lady Propane. One advantage that quickly becomes obvious is that you get to make a lot of “King of the Hill” jokes.

Chemically, propane comes from the distillation process when crude oil gets converted to gasoline. It’s a by-product. All of those flares and flames at an oil refinery? That’s propane being burned off. So in an environmental sense, you’re making use of something that is being underutilized in general, and making more complete use of an existing product. This doesn’t get around all of the inherent evils of the petroleum industry, but it does lend to a deeper effectiveness, which can’t be too bad.

Although it’s called propane what one really is buying is liquid petroleum gas, or LPG, which is a mixture of propane and butane (Hank Hill calls it a “bastard gas” for reasons we won’t get into here). LPG is readily available, although generally expensive, at U-Haul stores and RV centers. It’s much less expensive at places that sell propane (or more accurately LPG) for rural heating, etc. The last time I filled up the thirty gallon tank in the back of my truck, propane was three dollars a gallon. That’s about eighty cents less than a gallon of gas. When travelling in Texas, I use a book put out by the Propane Association that lists fuel sources in towns across the state. I’ve used it in trips to Houston and San Antonio, but should probably get an updated version. Odds are that most states have some equivalent directory.

LPG is pumped into a tank under pressure in liquid form. It turns into a gas somewhere around 20 degrees below zero Fahrenheit, but pressure keeps it a liquid. Propane burns clean. The exhaust of my truck has fewer hydrocarbons than a brand new car.
The conversion, if you are working with an older carbureted engine, is simple as well. Basically you’ll need four main components:

1. A propane tank – this needs to be sturdy and build for the specific purpose of storing liquid petroleum. It should include a blow-off valve and a gauge. I have a 30 gallon tank in the bed of my pick-up. Trucks are probably the easiest vehicles to convert because all you have to do is give up some bed space for the tank. Tanks are usually cylindrical, and can be found in auctions of state and municipal vehicles and their parts (many City of Austin vehicles run on propane) or in areas where there are lots of oil wells, as often oil riggers will have converted vehicles that make use of a cheap and plentiful gasoline by-product. The tank can cost a couple of hundred bucks, but often you can find them used for much less.

2. A vacuum shut-off valve—this is a safety device that uses engine vacuum when the engine is being started to release propane, which is under pressure, from the tank.

3. A vaporizer/regulator – this part has two functions, even though the propane is going to come out in vapor form unless you’re in a very cold place, it just makes sure by diverting hot water from the truck’s heater core in order to vaporize the propane. The regulator functions just like the regulator on a scuba tank, ensuring proper flow to the next piece you’ll need—

4. A mixer---what gets mixed is the propane and air. There’s a big diaphragm in the top of the mixer that helps with this process. Just like any air fuel mixture, somewhere between 16:1 and 18:1 is the ideal proportion between air and fuel. In my truck, the mixer is bolted to the throttle plates of an old Carter BBD carburetor to control the mix of fuel and air being sucked into the engine. Since the propane is under pressure, a fuel pump is not needed.
Important note: because of less density than gas droplet/fuel mixture usually found in an engine’s combustion chamber, you must upgrade your engine’s ignition system as well.

All told, parts for a conversion should run between $1,000-1,500.

--Clean burning and extremely small hydrocarbon emissions
--Since it’s already a gas, more equal fuel distribution to all cylinders
--Since under pressure, not effected by gravity, hills, etc (rockclimbers make extensive use of propane)
--Smoother idle, easy cold weather starting
--High octane (approx. 108) so engine’s compression and efficiency easily raised
--Unique and different
--Hank Hill references galore

--fewer BTU’s (British Thermal Units) than gasoline –poorer gas mileage by at least 33%
--fueling stations can be difficult to find
--really doesn’t save you any money
--need to buy yearly propane tax sticker (in Texas, anyways)
--hard to find knowledgeable mechanics—you’ll need to do most of your own work

It took me about a year to get all the bugs out, but I’ve been running w/ Sweet Lady Propane pretty much trouble free for two years now. If you can resign yourself to the poor gas mileage, and having to plan ahead to get a fill up, going propane is definitely recommended. I’ve got the satisfaction of driving an old vehicle but not pumping out hydrocarbons, and I’m driving something different that I’ve done all by myself.

Places for more info:
Raso Enterprises Alternative Fuels Discussion Board:
Info on Impco Propane Delivery Systems:

Franz Hoffmann’s Alternative Fuel Site: