Propane:  Page 1


How to Convert Your Engine to Propane

When I go wheelin' I am always surprised at the first questions to come out of people's mouths when they see my Jeep:  "What are those tanks on the back?"  I don't know, I guess I expected them to ask about axles, suspension, or something, not the fuel delivery.  But the tanks do kind of stick out I guess.

Anyway, when I tell them that the tanks are propane tanks and that my truck runs on propane, people become amazed ... they stare at me like I'm some sort of mad scientist and I might have a nuclear reactor under the hood.  I find this funny because, to me, propane is easier to figure out than both a carb AND fuel injection.  The next inevitable question to be asked is, "How does that work?"  In response, I write this article.  I hope it will educate those who want to know.  The first section will be a Pros and Cons section and the rest will be pics of my setup and explanations.  After reading, I hope people will see that propane is so simple that it is ridiculous.


LPG is the correct term for liquid petroleum gas, also known as propane.  In the world of wheeling, there are numerous reasons to convert to propane and, as far as I am concerned, only one NOT to.  We'll start with the pros:


  • LPG runs at any angle.  Since propane is in a gaseous state when it enters the engine, it is mixed homogenously with incoming air.   There is no float bowl to spill, no liquid for gravity to pull down and, therefore, no way to choke your engine.  This is extremely useful on those really steep hill climbs and off-camber side-hills. 


  • Simple and reliable.  Propane carbs, also referred to as mixers, are simple.  They vary depending on model, but even the most complex models have only a few moving parts and two diaphragms.  So to start off with there is very little that can go wrong with them.  But if something SHOULD go wrong with them, they're COMPLETELY rebuildable on the trail.  My carb can be completely disassembled, rebuilt, and reassembled with a simple flat-head screw driver in a matter of minutes.  There are no computers controlling them, so your not out of luck like the EFI guys are if their computer gets fried.  There's also no wiring to screw up for the average propane mixer.


  • Greenie-friendly!  The only byproduct of a properly-tuned propane carb is carbon dioxide, a naturally occurring gas that everyone releases when they breath.  If the greenies complain about that then they are truly insatiable!


  • Cooler engine temps.  My engine runs cooler, and cools down faster since I converted to propane.  I don't know if this is due to the extra cooling effect from running my heater hoses through the converter or just properties of propane burning, but it's a fact, man!


  • Cleaner engine.  Propane has little to no particulate matter in it.  It leaves no carbon buildup in the cylinders.  Therefore, your oil stays cleaner longer.  In fact, the recommended oil change interval for propane-burning engines is 13,000 miles!!!!  (And even then only due to viscosity breakdown.)  Even after 13,000 miles, most propane owners report that the oil they remove from the engine is still golden-clear like it was when it was put in!  This leads to ...


  • Longer engine life.  Some people say that the slow burn rate of propane as compared to gasoline wears down valves and valve seats quicker and therefore lessens engine life.  However, having hardened valves, as most engines manufactured since the 70's have, is reported to help, or even completely alleviate, this problem.  Since my engine is new, I can not attest to how many miles I have put on it.  However, I can attest to the fact that the man that I buy propane from runs propane on his 350 Tahoe and has put 435,000 miles on his engine without ever having had to turn a wrench.  His valves have never gone bad either.


  • 100% tank usage.  Propane is a liquid in the tank.  However, once exposed to atmospheric pressure, it expands into a gas.  Thus, even though the fuel pickup in a propane tank is at the bottom, as the converter regulates the pressure down to 4psi for engine consumption, liquid in the tank expands to fill the void left.  Therefore, when your tank gets low, it continues to suck fuel in through the pickup.  Even though the liquid may slosh around, it will not result in your pickup running dry.  Getting on a steep incline and having your engine shut off because all the gasoline sloshes away from the pickup sucks.


  • 110 octane rating!!!!  Propane is rated at 110 octane.  Does your engine have pinging problems?  Is your high compression ratio causing you to have to run expensive 93 octane to keep the pings away?  No more worries there, buddy!  Engines built to run propane have been built with up to 16:1 CR!  Mine is 10.25:1 and I have ZERO pinging.  This also means you can advance your timing to get that extra power!  It's as close to racing fuel as you can get without running racing fuel!


  • Easy to tune.  Propane is easy to tune.  Once I got my timing right, my engine started up and idled perfectly after over a year sitting.  The nature of the mechanics of a propane carb will not let too much or too little fuel enter the engine at idle.  Sure, the idle speed can be adjusted slightly with the carb, but for the most part, if you have the correct carb for your engine CID, most of the time the idle is within 250 rpm of where it should be before tuning even begins.  To tune it correctly, I just closed the fuel metering valve in the carb as far as it would go and revved my engine to 6000 rpm.  It skipped a little, so I turned it up until it stopped.  My engine roars all the way up to 6000 rpm with ease now with the stock GM HEI!



  • Hard to find refill stations.  This is not 100% true, although I do have to admit that it is probably 70% true.  As a propane runner, I can not just borrow gasoline from someone on the trail if I run out.  I have to plan my fuel consumption and fills a little more than gas users do.  If I'm going somewhere for the weekend, I have to know in advance if there is somewhere that I will be able to fill my tanks.  If there is not, I have to bring spares.  This problem could be solved either by just getting a big enough tank to fuel my needs for an entire weekend or by not running fork-lift bottles.  Even though they hold less fuel, conventional grill tanks can be used and exchanged out at most gas stations anywhere.


  • Loss of power.  I did not find this to be true at all.  As compared to a perfectly tuned carb, converting to propane will result in a small loss of horsepower at the top end of your power spectrum.  However, it has been true of the vast majority of gasoline carbs that I have known to not have been tuned properly to begin with.  Tuning those things is not easy, much less getting them tuned perfectly.  Many people that convert to propane actually report a GAIN in seat of the pants hp!  This is because propane carbs are simple to tune to max efficiency.  Once you get them tuned properly, there will be no way for your engine to suck in too little, or too much fuel.  That and the ability to advance your timing will compensate for, if not completely eliminate, any loss of power.


!!!01/15/06 - UPDATE!!!:

Recently, or to be more specific, a long time ago, a veteran of the LPG industry contacted me to educate me on some topics that were discussed in this article.  My lack of free time has resulted in a severe delay in getting the info here.  Some additional things that I would like to point out are:

  • While it is technically possible to use 20# grille tanks with a system as outlined in this article, it is not recommended.  This is because they do not have a special excess flow valve on them that will severely reduce the LPG flow in the event of a line being severed.  Certified motor vehicle tanks, such as the forklift tanks used in this article do have the valves and are therefore safer.

  • Again, while a lock-out valve is no a technical requirement, it is HIGHLY RECOMMENDED as a way to stop fuel flow during an emergency.

My thanks go to Sandy Kicliter both for reading my article and offering his years of experience to me and my readers.  I hope to someday wheel Moab with him.


Enough chit-chat!  On to the tech!