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Joe and the Propane Tank

News flash! Could Joe and his truck be the next satellite to orbit the earth?

On this week's Car Talk, we heard from Joe in Charlotte, North Carolina. Joe's uncovered a 100 pound propane tank, complete with a compressed natural gas converter, strapped to the underbelly of his Ford F150. Is it safe? And, if it is, is it actually cost-effective to run his truck on propane?

What do you think?

Join the discussion and let us, and Joe, know. Assuming, that is, that he isn’t currently busy calculating reentry angles.

Since the early 1960s at least, nearly every taxi in Japan has run on liquid propane gas (LPG). I lived in Tokyo from 1959-67 and rode in many of these taxis. The only time I was aware that a taxi was running on LPG was when the driver opened the trunk to store luggage and I’d see that the LPG tank occupied nearly the whole space. I never heard of a tank exploding.
Jim Shaw
New Bern NC

I work for a natural gas utility company in Michigan and several years ago we had an extensive Compressed Natural Gas (CNG) vehicle conversion program; we had several hundred fleet vehicles of all makes running on CNG/Gasoline or dedicated CNG. The program was not a financial success so after several years we dropped the program - of course gasoline was only $1.25/gallon then - that had a LOT to do with it. Anyway, the first thing you need to get straight is that CNG and Propane are NOT the same. CNG is compressed natural gas - methane - and stays a gas even at operational pressures of 3,600 psi. Propane is liquid propane, is liquid in the tank and used at about 20 psi or less. They are NOT the same, not interchangeable, tanks parts etc., can only be used with one fuel - although there have been vehicles with kits and tanks added for propane and CNG along with gasoline. LNG - becoming more common today, is Liquified Natural Gas which is a cyrogenic process, not a pressure process - also is a completely different system. So, does the truck have a propane or CNG system? From what I heard on the show, it sounds like it’s a CNG system, not propane. Regarding SAFETY, natural gas at 3,600 psi is far safer than gasoline! The noise of rapidly blowing gas might be scarry - but try lighting a torch if the gas pressure is too high… you can’t do it. Natural gas is lighter than air - it goes up and by the time it is mixed with enough oxygen to be flamable it’s going to be way up in the air, not laying on a puddle and saturating vehicles and people with liquid fuel that is easily lit. Also, look at the tanks! Why would you ever think that a rock from the road would cause a tank leak?? That is crazy - all the fuel lines are stainless steel rated for the pressure too. Compare that to flimsy thin gasoline tanks of light metal and plastic and plastic fuel lines - that is the DANGER. We used to say that if we grew up with CNG vehicles and somebody tried to convert us to gasoline we’d throw them out as being crazy for suggesting such a dangerous fuel. CNG tanks have been shot at and drop tested; they been poven to be far safer for police cars and every other vehicle than gasoline tanks. Regarding sales, CNG should be sold by the GGE - gasoline gallon equivalent. If it is sold by the pound that is archic and out of touch - but I think the conversion factor is about 5 pounds CNG = 1 gallon for gasoline, so the cost quoted by the caller of 3 something per pound is not correct - it would be more likely to be 3 something a gasoline gallon equivalent and then they provide the approximate pound conversion. CNG must also be temperature compensated. I forget the exact conversion factors without looking up my old charts of pounds, BTUs, gallons, etc. The disadvantages of natural gas is that the tanks are large and heavy, the fuel density even at 3,600 psi is far less than gasoline so the tanks must be big and don’t go as far as the same volume as gasoline - and the conversion or add-on cost of the equipment - esp for dual fuel where gasoline must also be used. I hope this helps. Bob

A simple web search (no, I don’t use Google…I use a search agent) pulls up a world of info. It’s almost as interesting as biodiesel or homebrew electrics.

Try starting at and go from there. Even the State of North Carolina has a web page about CNG even though it is dated (vintage 2004). CNG and LNG aren’t trendy like other alternative fuels to gasoline. It doesn’t have the appeal of, say, ethanol or biodiesel because it doesn’t come across as ‘green’.

Warning - Editorial: Sadly, the side effects of the so-called green fuels may make a fuel like CNG/LNG a better near-future alternative. Too bad no one insisted on studies as comprehensive as those thrust upon other industries that would have revealed the effects that biofuels are having on the economy and food supplies. I guess if you can label it ‘green’, it’s always go not matter what the consequences. Oh, and has anyone investigated what the repair costs are if something goes wrong in a hybred vehicle? Try pricing the transaxle assembly in a Prius.

(Stepping down from soapbox)

Hickory, NC

Gentlemen and other readers/listeners:

I overheard this topic discussed on this morning’s show on WXEL in South Florida, where I live and I MUST answer, since I actually have a car fitted with a dual-fuel system. Mine uses compressed natural gas (CNG) and regular gasoline and was fitted with the system in Canada, like Joe in Charlotte’s truck. The fact is that CNG systems are quite safe and widely used; the storage tank under the truck is NOT going to explode since CNG is stored at pressures of 3000 or 3600 pounds/square inch. This doesn’t mean that you couldn’t detonate one of them if you were trying to, though. Ford F-150s were one of the most common truck conversion models; most CNG conversion cars/trucks in the US were former federal, state or local government fleet cars, although some large corporations used them too. They’re also popular for municipal buses. The chief advantage of using CNG is the fuel is both cheaper and produces, at least theoreti-cally, up to 70% less CO2 emissions than gasoline (1 gallon of gas yields >19 lb. of CO2 but one gge (see below) yields 5.66 lb. CO2). You don’t sell or buy CNG by the lb. either (as Joe had suggested), but rather by the gasoline-gallon equivalent (GGE) which is equal to 5.66 lb. of CNG. CNG is mostly methane (CH4), the simplest hydrocarbon.

I doubt the vehicle is actually propane-equipped, as both Tom & Ray and the caller suggested, since propane is a 3 Carbon molecule (actually, the formula is C3H8). If it is (and propane conversions DO exist and are for sale occasionally), this is good, since propane is MUCH more widely dis-tributed than CNG and is usually cheaper than CNG, meaning he could buy it almost anywhere campers and RVs are sold. Propane does release more CO2 into the air than CNG, however.

I’ve paid as little as $1/gge of CNG (formerly in Ft. Pierce FL), but am now currently paying $2.32/gge in Sunrise FL (in contrast, gasoline in South Florida sells for ~$3.50/gallon). If Joe has a natural gas line at his house, he can invest in an automatic compressor called a PHILL (which sells for ~$1500) which can fill his truck overnight in his carport while he sleeps and only pay the houslehold rate for natural gas he now pays to heat and cook. This is usually MUCH less than CNG bought at a filling outlet and may even drop his rate to $1.00 per gge. I think the price Joe was quoted most likely was for a gge of CNG. A big advantage of CNG is that you only need to change the oil every 10,000 miles or so (it burns much cleaner than gasoline), so maintenace costs are lower. Also, estimates that CNG conversions add $3000-$4000 to the value of used cars and trucks, so Joe up in Charlotte may actually be sitting on a Gold Mine. If he feels he must sell it, EBAY auctions for CNG vehicles are widely followed in the alternative fuel community and he might even be able to make a profit by selling it that way.

Good morning- My brother had a cng/gas car for years. Very dependable. Fuel cost was slightly less than gas
but the milage was less also. I think the BTU output is less for cng. Because of the clean burn the carbon created inside the engine is greatly reduced. Engines run on cng have longer lives because of the reduced wear on parts. BobFegan and jpcaru’s notes are well written and refect my brothers positive experience with cng. Jeff Salem, Oregon

I posted this in another part of the forum and it should have been posted here:

I worked for the upfitter that installed these systems for Ford. This was a factory approved installation sold through certain Ford dealers. The tank is either a 3000 or 3600 PSI Compressed Natural Gas tank with a kevlar wrap, VERY STRONG, so no worrys about an explosion. CNG can be cost effective but actually has less energy density than gasoline, it is cleaner to burn and doesn’t have the byproducts that dirty the oil. These were originally sold to fleets. The same company that built that system also provided systems for the Contour also in a “bi-fuel”(gasoline & CNG) configuration, as well as a CNG only pickup, also they produced an LPG bi-fuel pickup. Here’s the bad news, the tanks for CNG are only good for 12 years, and then must be replaced, the expiration date can be found on the tank, if its expired it should not be used, drive it until its empty then don’t use it until the tank gets replaced! The LPG models had the tank in the bed only. You have to run a tank of gasoline at least every 90 days, keeps the fuel injectors from gumming up as well as keeping the fuel from going bad. These systems were built by GFI from Kitchener, Ontario and were installed by Transportation Design & Manufacturing.


Hello to all: Today was the first time i had ever listened to CarTalk during a brief ride to my office and i must say, as a recent newcomer to the NPR listener audience, i am starting to become comfortable in admitting to myself that i dont need big subwoofers and a fancy stereo to impress people, but rather to use the knowledge and wit i gain from listening to the programming. In any event, i will partake in this discussion as it brings up a very interesting point. In my experience, having lived and visited many parts of the world and being fortunate enough to be able communicate with the respective citizens i have the basis to say that the joke that was refered to regarding the propane tank blowing up points out the true narrow-mindness and over-political attitude that this country has. Let me explain:

Coinciding with the aforementioned posts, CNG is used in a plethora of countries around the world, and is mentioned in conversation much the same way as gasoline would here in the States. In Argentina for example CNG is offered in literally every other gas station. The interesting part is however, that to my knowledge, new CNG-powered cars that are sold in that country are not the major demand source for the fuel, rather, much like the example brought on in the discussion topic, the demand stems from individuals modifying their current car to run on both gasoline and CNG. Doing so costs roughly $800 USD, and believe me, in that country it may equal to many people’s 3-month salary. Even with this factor, you will not find lack of business in any “shop” that performs these alterations. On average they say it costs roughly 2/3 as much as running on gasoline alone. Diesels cannot be converted, as they are spark-free, and under the after-market modification procedure, the car cannot be started with CNG, the lines need to be activated once the car is running. I tell you what, from the impressions that i received, people love them. With a lack of performance, less calculated mpg, and an obtrusive tank in the trunk of your car, if youre not the guy thats holding up your foursome buddies at the links because you had to spit shine a bug encounter on your fancy sports car’s windshield resulting in a grand theft auto like dash to the course, its a no-brainer.
But the sad fact is that apparently our country represents “that guy”. Think about it. We think we are all that and a shaken martini rinsing a crackered caviar. Although we may have that fancy sports car, an appeariangly large bank account (we’ll call that a large line of credit), and a gorgeous english babe at our side, we are the same person that gets up to the tee with confidence, a smile, and a driver that could have been a conceptual representation of NASA’s latest propultion lab’s experiment. And then what happens: well we take an infinitely long time taking our practice swing, checking the wind using the latest sharper image or skymall gadget, adjusting our stance to the nearest millimeter (remembering all the tips you read about in magazines sitting at the john). Your buddies in the meantime are putting for par in the next hole; and at that point in time, just when you realize you might need a new group to join-in, you take a hack at the ball, completely shank it, and end up hitting in the mouth the mentaly handicapped “landscape beutitian” whose only savant"ish" gift was to have the ability to communicate with ducks and other course-dwelling animals. You know, for someone whom you at least thought had a high regarded rank amongst its peers, you would think that this would be the last place you’d end up: the main topic in every local (eventually national, what else would the media use that would be so attention grabbing) conversation.
Sadly, i feel that again, we are that guy. If you have made it this far in my post, you must have been creative enough to decipher some of my analogies and personalifications throughout, and there was a lot. If not though, i would be more than happy to address them, give examples, and possibly even share a conceptual idea of how we can change other’s perceptions of us from being “that guy”.

Hi Tom and Ray,
I heard your show recently and had to comment on your CNG LPG story. I live in Germany and drive a Ford C-Max (kind of looks like a Galexy that was too long in the dryer). We have converted it to run on LPG (and Normal Super) or as it is called here Autogas. Do a Google search using the term “Autogas” and you will see how much it is used here in Europe. In England, Poland, Italy, Holland, Germany, and Austria it is growing in use. CNG on the other hand has problems in that you can only open a gas station were ther is a pipeline. It does not matter if you use CNG or LPG there is a percent power loss. You also need more of the gases as apposed to Normal gas. You can find out more info at: Autogas is sold here in Liters and CNG is sold in Kilos. The Injectors that are used in our Ford come from Poland where there many more LPG driven cars than here in Germay. Each Year over 2,000 new LPG gas stations open up and that number is increasing. I will let you know how our car is doing when we have our “final adjustments”. Then we will see how much more “Gas” we will need in comparrison to Super. The values that come out of the Tail pipe with LPG are more “Green” than Super could ever hope for.

I drive a small Nissan Micra in London. It has a 1.0 litre engine. About 3 years ago I had it converted to LPG (liquified petroleum gas), which is a mixture of propane and butane. In Europe it is usually known as Autogas. The car is now dual fuel - it will run on liquid gasoline (or petrol, as we call it) or LPG. If it runs out of LPG, it automatically switches over to petrol - there’s a small micro-switch on the dash. LPG costs about $1.10/litre in England. Petrol costs about $2.20/litre. Although the gas mileage with the LPG is not quite as good, the cost makes it much more economical. But the real advantage in London - this is the reason I had the car converted - is that LPG cars are exempt from the London congestion charge. If you want to drive into the centre of London you have to pay a $16.00 daily charge. In my Micra (even if I’m running it on petrol!), I don’t have to pay the charge. It cost me $3600 to convert the car, but over the last three years I have saved about three times that much by not having the pay the congestion charge. I don’t know how much I’ve saved on gas - I’m not that obsessional. The LPG tank is in the trunk (we call it the boot) where the spare tire used to sit. The spare tire is now in the main part of the trunk, which means there’s no room for anything else. If you have an LPG tank you’re not allowed to take the car through the Channel Tunnel (under the English Channel). They tell me the tank is safe, but I wonder why the Channel Tunnel people disagree. I listen to the Car Talk podcast on my Ipod - my wife thinks I’m nuts, and I think she’s right.

Here is some good info on this subject- In this month’s Best Life Magazine, in the Cars section, it reports that Honda offers now a car that runs on compressed natural gas and the fuel is half the price of gas in most cases, abundant, domestically produced, and very eco friendly. The majority of the American homes are already on natural gas and once company offers a home based natural gas machine that hooks up to home lines-The Phill from FuelMaker costs about $4000 and can refill a car overnight.

Honda has had ben producing CNG powered civics for about 4-5 years. No new news. In my opinion it makes a helluvalot more sense to own one of those vs. a hybrid.

We listen to your show on KUFM in northwestern Montana and we love you guys! In 1999-2000 my wife & I were lucky enough to celebrate the millenium and our 30th wedding anniversary with a memorable six-month trip around the entire continent of Australia. We bought an old Toyota camper that was equipped to run on either gasoline or LP gas, and we re-sold it at the end of our trip. We were amazed that even then gas stations all over Australia sold both gasoline and LP gas, most of them with self-serve pumps! Not as many gas stations had LP gas, but we rarely had trouble finding it, even “out beyond the black stump.” The LP gas was somewhat lower in energy content per liter, and gave slightly poorer performance in acceleration, but it was cheap enough to be more cost-effective than gasoline. We heard the odd anecdote about the car that had supposedly blown up, and we ran into two or three gas station owners who refused to let us pump our own LP gas, citing safety concerns. But we never read or heard any authentic accounts of LP gas disasters in the time we were there, so I suspect that such problems were as rare as with gasoline. My question: if the Aussies have been doing this for at least a decade now, why are we so backward in adopting alternative fuels in the U.S.? I fear that we Yanks are falling behind the rest of the world because our big entrenched corporations are stifling innovation. Keep up the great programs!
Don Schwennesen (rhymes with venison)
Bigfork, Montana

I agree with you. Refer to my post above about “that guy” in evrybody’s golf foursome. …we are still looking for our ball…

Compressed Natural Gas is a great alternative fuel. As the others have posted, it is an inexpensive, abundant, domestic resource which burns very clean. We have 3 of them in our garage. Here in Utah the public pumps dispense at 63 CENTS PER GALLON. In Oklahoma they pay 91 cents per gallon. Most pricing around the country is better than half the price of gasoline. The Honda Civic GX has been rated the cleanest vehicle on the road for 5 years in a row.

The caller should find a CNG certified mechanic to inspect his tanks (they do expire after 20 years), and if all is well he should by all means use this fuel if it is available in his area.

Propane tanks are used safely on motor homes and camper trailers. I don’t see why one on a truck would be unsafe, unless it is allowed to deteriorate beyond safety standards that RV users must follow. Those who refill propane tanks have strict rules they must follow. The valves must be safe and there can be no rust on the tanks. If they are unsafe, they will not fill the tanks.

Hi Tom & Ray!

Hello Joe,

I got a semi-frantic call from my girlfriend yesterday morning as she was listening to KPCC and heard your predicament. She felt that I should respond to your question. So, to make mama happy (everybody knows if mama ain’t happy, ain’t nobody happy), here’s my $0.02:

The first thing to do is determine, exactly, what system does your F150 have? CNG or Propane? Ford sold the F150 with a number of bi-fuel options, e.g. gasoline & CNG, gasoline & LPG (propane).

From clues given, I would guess that you have an F150 with the bi-fuel CNG option. The difference between these two alternate fuels is that CNG is mostly methane (CH4) while LPG is mostly propane (C3H8). OK, wise guy, tell us something we don’t know! I can almost hear everyone saying. Well, the system operating pressure makes the big difference. LPG systems are 100-150PSI while CNG systems are either 3000 or 3600 PSI.

For now let’s just say you have bi-fuel CNG F150. If the CNG option does not work, it is most likely the combined metering valve and computer (compuvalve). This component’s location is immediately downstream of the pressure regulator and it is also downstream of the VCL (vehicle communications link module). It is located in the engine compartment on the passenger-side of the vehicle. Integrated in the compuvalve are pressure & temperature sensors as well. With all these connections & functions, you can probably gather that if the compuvalve ain’t happy, ain’t nobody happy.

The compuvalve was made by Teleflex GFI of Canada but you will not be able to buy it directly from them. This & other CNG-specific devices are made by GFI, exclusively, for Ford. In short, it is available from your local Ford dealer$hip only so just drive it on gasoline mode - unless you decide move to OK or UT where CNG is under a dollar per gallon, then it’s worth fixing.

If you are concerned about the CNG components remaining on your truck, Natural Gas Vehicles or NGVs are very safe. Learn more about the CNG systems by watching this 13 minute video (large file download). You can also learn more about NGVs at this website

Since 2004, my personal vehicles have been OEM 100% electric vehicle or dedicated natural gas (CNG only) vehicles. These AFVs are fun to drive and offer challenging maintenance work. Should you decide to take the red pill, contact me directly at Google mail (same ID), and I will try to help you as much as I can via e-mail. And if you do not care to keep the CNG components, I would be happy to take them off your truck & off your hands as well!


referring to the caller with the CNG tank on his pickup, the energy density per pound is greater for CNG than gasoline. CNG is 53.6 MJ/kg and gasoline is 46.9 MJ/kg. (

You had a caller who was puzzled/concerned by what sounds like a CNG rather than a LPG system in his pickup. A good source of information and advice would be the local natural gas utility, which in his case would be Piedmont Natural Gas, if I am correct that he was calling from Charlotte. Another source of information and referrals might be the American Gas Association’s website, <>. I also think he mentioned that this had been a fleet vehicle. Many natural gas utilities equip operate their light vehicles with natural gas/gasoline dual-fuel conversions, so this truck’s origins may be the local utility. Since there are very few retail filling stations in the USA that supply natural gas, that can be an impediment to taking advantage of any potential economies that may exist in Joe’s market. However, if Joe has natural gas service at his home, he or the local utility may be able to install filling equipment if it has such a program. Such programs are few and far between in the USA.

These trucks are fairly common. I noticed one guy that replied worked for an upfitter that set them up. They were listed for several years in Ford’s F series brochures and came in F150’s and F250’s. I’ve seen some 650’s and 750’s running on propane as well. The local propane distributors just about all run their trucks on Propane. Schwann’s (The yellow trucks that peddle ice cream around the neighborhood) run on propane. Schwann’s advertises that it’s entire fleet is propane powered. Middlesboro, KY Coca Cola bottling plant ran it’s trucks on one of the two, I don’t remember which, for years, and I believe yet has some gas trucks.

For the F-series Fords, there were some that were propane and some that were CNG. Joe needs to make positively certain which he has. The 2 gasses aren’t compatible or interchangeable. For instance a Warm Morning gas stove can run on either fuel, but you have to change the orafice out to change fuels. The orafice is a ball stop in the line with a hole through it. The size of the hole varies between the 2 gasses and the size of the stove. I assume that in a vehicle, it’s likely not that simple, but the long and short is, if you put the wrong fuel in with the wrong system you’ll either create something that won’t run or will blow sky high from having too much fuel.

There are lots of vehicles that run on gas not to mention equipment (Most fork lifts are propane powered). The safety isn’t an issue. As was said, a typical gasoline tank is made with sheet metal while a compressed gas cylinder is 50,000 times stronger than that. Think of a dive cylinder v’s a typical gasoline tank. There’s no comparison in strength.

I actually thought seriously about buying one of these trucks once. (CNG Truck) A local dealer had one (96 model I believe) on their lot and had it discounted down in a big way because they were having trouble selling it. This truck was listed as an F150, but it was on the light duty F250 chassis that Ford made for 1 year before they came out with the current look F250. The advantage I had was owning a farm with a gas well on it. I thought I could hook a pump to my well and fill my truck up F.O.C. (free of charge). I got to checking on what would be required to fill the cylinder and at the time the pump was astronomical. It would have cost in the tens of thousands to set it up. No way to recover that much expense, plus getting it on the road away from the farm would have been an exercise in futility to find fuel.

The thing about it, CNG would be a much more practical option than the nutty ideas we keep coming up with like Bio Fuels that are doing nothing other than sucking up tax money in incentives to produce it not to mention driving the price of corn, soybeans, and other grains through the roof that will result in higher beef prices, higher cereal prices, and currently bio fuels take about 1 gallon of fuel to produce 1 gallon of bio fuel. Hence, we aren’t going forward.

The thing about Natural Gas is it’s plentiful enough to run vehicles on, vehicles can be set up to use either natural gas or gasoline, so it provides some hedge against oil companies artificially increasing prices. It’s cheap to ship, at least relative to gasoline, and wouldn’t require delivery trucks to haul it from terminals to stations. Likely the biggest problem is the government hasn’t figured out how to road tax it yet without taxing people’s home heating gas. Owning a farm with a well on it, I can say that in recent years, the Arabs have been buying up wells and systems throughout this area from the original developers. I suspect they realize the potential and plan to eventually cash in on it. One of my questions to the dealer was, “If I buy this truck do I have to buy a fuel user’s bond and pay road tax in some alternative method.” The answer at the time was “No”. At close to 50 cents a gallon in road tax on gasoline and diesel, the government is not going to be inclined to promote such a system until they figure out how to tax it like everything else.

I’m sure his truck is perfectly safe, although it’s likely not practical for an individual to use the CNG system. Gas utilities and propane distributors have the advantage of at cost fuel to burn plus the money to invest in the facilities to fill the vehicles, and their trucks generally don’t get more than a few miles away from their plant.