I did a search here and couldn't find an answer to this question: Why can't I use a forklift propane tank in a car? I found a deal on a 100 gallon propane tank that has never been used. With the rising cost of gas, I am seriously looking into this. I can get propane for $3.28 a gallon here, where gas is quickly tickling the $4 mark.

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If it was easy, everybody would be doing it.

I have a slant with LPG. Because the high gasoline prices this part of the world (about 8 dollars a gallon) it is very common here.


You need some extra stuff under the hood though, and depending on the type of equipment you use you may get a little less power. Most of the converted cars use a bi-fuel system, so its still possible to drive on gasoline.

Do NOT use a DOT lift truck cylinder in your car. It is dangerous and illegal for on-road vehicles. For trunk-mounted tanks, you must use an ASME motor fuel tank with a vapor box around the fittings. See my Propane Fuel Tank page for more information.

A trunk-mounted tank will look like this when it is installed:

Is that because the lift tank won't vent properly if it leaks? Or is there something else inherently dangerous? Just curious; you know a lot about this stuff. I just went on the thinking that the off road guys are using propane and they use lift tanks. Mine would be open to the atmosphere more or less, under the tonneau of my pickup.

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If it was easy, everybody would be doing it.

Yes, venting has a lot to do with it. Motor fuel tanks with vapor boxes vent to the outside of the vehicle. Besides that, the vapor box prevents any vapors from leaking valves from accumulating inside the vehicle where the spark from a door contact (for example) could ignite it.

Another reason is that the tank brackets on a lift truck tank were never designed to withstand the g-forces from a collision. There are very good reasons that NFPA 58 requires the things that it does. I highly recommend that you buy a copy of NFPA 58 and understand it before doing anything.

One reason that the off-road guys like the DOT cylinders is that they can change an empty tank on the trail without having to drive back to a propane station for a fill. Motor fuel tanks are generally much larger than lift truck cylinders so the chances of running out of fuel are much slimmer. The largest tank that you can fit in a pickup truck (with a long box) is a 310L (82 USG) 24x60 tank. You can probably fit an 185L (48.9 USG) 18x62 tank under your tonneau cover.

Your tonneau cover could easily contain the propane vapors in your bed so this would be a good application for a tank with a vapor box and a remote fill valve.

BTW, are you sure it's a 100 gallon lift truck cylinder? The largest lift truck cylinder is a 43.5# tank (9.9 USG of LPG). You can see more on Manchester's Lift Truck Cylinder page. Portable fuel tanks for heating purposes are available in a variety of sizes including 100# (22.9 USG). These tanks are useless for motor fuel because they're designed for upright VAPOR WITHDRAWAL and motor fuel tanks are all LIQUID WITHDRAWAL.

You are correct, sir. It is not a lift cylinder at all. I went and looked at it, and it is a giant propane tank for a camper.

You have talked me out of trying the lift tank idea, though. I looked on youtube and saw some propane explosions. Not good! If I do this, I want to do it right, and I am many dollars away from it right now. With gas prices rising like they are, though, it won't be long before it is cost effective. I bookmarked your page for further reading.

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If it was easy, everybody would be doing it.

You might be interested to read a topic on my propane forum about a Volvo conversion that used a lift truck cylinder. He ended up replacing that tank with a proper motor fuel tank later on.

Thanks for the tips! I do want to do this, but I do not want to blow up! I guess I have to save up the money and do it right. That means four dollar a gallon gas for a while longer. Sigh.

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If it was easy, everybody would be doing it.

Frank,
What would be wrong with using the 20 pound cylinders that are available at every gas station? If they can sit in my trunk on the way home from the store, why can I strap it in my trunk with a proper bracket?

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Chris'
Autobody
Restoration
Service

First off, the 20# barbecue cylinders only supply propane VAPOR. Vehicle systems require the tank to supply LIQUID to the propane converter where it is then vaporized and regulated to produce a low pressure gas.

Second, while you can transport a 20# cylinder in your trunk, you don't want it in your trunk any longer than you have to. The relief valve will blow off vapor into your trunk if is upright. If it tips over or you mount it upside down to get liquid out of the tank, the relief valve will vent liquid into your trunk and propane expands 270 times as it vaporizes. I certainly wouldn't want to be near your car if this happens.

Third, there is no proper bracket that you can use for this application. A lift truck cylinder has a specific bracket that is designed for use in lift trucks. NO propane code allows this type of tank in a motor vehicle. Period.

As I said before, DOT tanks are illegal and dangerous for use as motor fuel tanks. If you use this type of tank in your car and you get into an accident, you can have a major liability. In the grand scheme of things, the cost of a proper fuel tank is quite small compared to the amount of fuel that you will be consuming. Do it right the first time.