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Old 08-10-2018, 12:33 PM   #1
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Propane powered bus - leave propane or convert to diesel?

I'm looking at buying a bus that is currently powered by propane. Owner says it would be relatively inexpensive to convert to diesel but that I can find propane fill stations across the country.

We currently live in a motorhome and travel full-time. We mostly dry camp in BLM or NFS areas and rarely go to "big" cities.

I've been researching but not finding a lot of information. Are propane fill stations very readily available? Can most large propane companies (thinking something like Amerigas, etc.) fill the tanks? Is it better to convert to diesel?

If better to convert to diesel, does anyone have a link on what needs to be done to do the conversion and a guess as to how much it would cost to convert?

Thanks!!
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Old 08-10-2018, 02:34 PM   #2
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Propane is not usually sold in places like 24hr gas stations. Separate fuel companies or places like TSC will only help you during business hours. So that issue of availability would be a concern.
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Old 08-10-2018, 03:37 PM   #3
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"Owner says it would be relatively inexpensive to convert to diesel". Relative to what? Repowering the bus with a different engine is never inexpensive! Unless you plan on never being more than a few miles from home with it, buy a diesel bus.

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Old 08-10-2018, 04:30 PM   #4
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Diesel buses and trucks are regularly converted to run on propane or CNG the largest fleets in the world have "LP diesels" or "CNG diesels" running daily in their fleets the conversion is fairly simple there or back. Most places that fill tanks larger than BBQ tanks can fuel your unit including all the majors most co-ops TSC and almost every small town has a propane supplier.The only real consideration is cost LP or CNG is cleaner than diesel and doesn't jack up the newer diesels as bad if at all but if I remember the btu avail is slightly lower than diesel but don't quote me on that if my diesel was LP I would leave it that way. Gene
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Old 08-10-2018, 06:42 PM   #5
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I thought propane ran with much lower compression more like a gas engine not a diesel? I know diesels can be built to run on propane or LNG but thought they were built with low compression?
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Old 08-10-2018, 06:47 PM   #6
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forgot need some spark plugs too for propane, so they would have to go away....
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Old 08-11-2018, 09:38 AM   #7
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Thanks, guys! We eventually decided to go with a diesel van-chassis bus instead of the propane conventional bus. The Wife thought it would be easier for her to drive the van chassis bus and decided she didn't want anything as big as the conventional bus
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Old 03-18-2019, 12:29 AM   #8
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Originally Posted by Gdog 5651 View Post
Diesel buses and trucks are regularly converted to run on propane or CNG the largest fleets in the world have "LP diesels" or "CNG diesels" running daily in their fleets the conversion is fairly simple there or back. Most places that fill tanks larger than BBQ tanks can fuel your unit including all the majors most co-ops TSC and almost every small town has a propane supplier.The only real consideration is cost LP or CNG is cleaner than diesel and doesn't jack up the newer diesels as bad if at all but if I remember the btu avail is slightly lower than diesel but don't quote me on that if my diesel was LP I would leave it that way. Gene

I suppose the question is, is the bus engine in question a converted diesel or a converted gas engine.
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Old 03-18-2019, 01:28 AM   #9
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1 gallon of diesel burned produces 139000 BTUs, gasoline 124000 BTUs propane (LNG)91600 BTUs, and CNG only 900. The average price of diesel right now is $3.01 a gallon, average price of propane is $2.32. That's a 30% difference in price but a 50% increase in power with diesel over propane
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Old 03-18-2019, 09:16 AM   #10
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Since a propane engine needs spark and some method of getting the gas, not liquid, into the engine, converting a diesel to run on LP would be quite an engineering and machining feat. You would need to lower the compression ratio, put spark plugs in somewhere,come up with some sort of spark delivery system, come up with some sort of fuel delivery system then make it all work together somehow. There are "kits" on the market that advertise diesel LP injection. Those run from simple to complex and will add some needed HP for climbing hills, etc. They DO NOT convert a diesel to LP, it's still a diesel running on diesel. All of them simply add LP to the intake system to add some extra btu's to the mix.

On the other hand, converting a gasoline engine to LP is relatively simple. There are plenty of kits around to convert one and two cylinder engines. The compression ratio is pretty close, the spark ignition is already there and there is a fuel delivery system of sorts. To do it right you also need to change cam timing. Back when we had carburettors it was really easy. There were kits to do it that were relatively inexpensive. the good ones also had an oil injector because, LP has no lubricating qualities (I'm not sure todays gasoline lubricates all that well but, that's a different discussion). If I remember correctly they just dumped LP into the top of the carburettor. Any of you other old farts remember these? We had two customers that had them but, that was a loooooong time ago.

You could probably do something similar to a fuel injected engine but, with todays computer controlled everything again much engineering and programming would be involved. I've not seen any kits lately for a car/truck engine.

Dick
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Old 03-18-2019, 01:43 PM   #11
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Since a propane engine needs spark and some method of getting the gas, not liquid, into the engine, converting a diesel to run on LP would be quite an engineering and machining feat. You would need to lower the compression ratio, put spark plugs in somewhere,come up with some sort of spark delivery system, come up with some sort of fuel delivery system then make it all work together somehow. There are "kits" on the market that advertise diesel LP injection. Those run from simple to complex and will add some needed HP for climbing hills, etc. They DO NOT convert a diesel to LP, it's still a diesel running on diesel. All of them simply add LP to the intake system to add some extra btu's to the mix.

On the other hand, converting a gasoline engine to LP is relatively simple. There are plenty of kits around to convert one and two cylinder engines. The compression ratio is pretty close, the spark ignition is already there and there is a fuel delivery system of sorts. To do it right you also need to change cam timing. Back when we had carburettors it was really easy. There were kits to do it that were relatively inexpensive. the good ones also had an oil injector because, LP has no lubricating qualities (I'm not sure todays gasoline lubricates all that well but, that's a different discussion). If I remember correctly they just dumped LP into the top of the carburettor. Any of you other old farts remember these? We had two customers that had them but, that was a loooooong time ago.

You could probably do something similar to a fuel injected engine but, with todays computer controlled everything again much engineering and programming would be involved. I've not seen any kits lately for a car/truck engine.

Dick
I had a van on dual gas/propane ( still have it but use it for storage now ) -not sure of the mechanics of it, but to switch from one fuel to the other was a simple as literally clicking a switch - also had a one ton flat deck on duals that was 100% propane - I traveled to places like Ft Simpson and Yellowknife in the NWT, from south east BC, across the prairies to Manitoba, then north heading to Ft St John in northern BC, and also travled south to Truckee Ca with the same truck,
and the only time I had trouble getting propane in the remote areas was when I didn't check ahead for availability, or one time when I didn't take into account how strong the head winds were and how much it would affect my high load - that was a good many years ago and I would imagine things have changed for the better over the last 30 +/- years
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Old 03-18-2019, 02:18 PM   #12
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To convert a diesel to CNG, you litteraly take the injector out, replace with spark plug, install ignition system and a throttle body with fuel injection, CNG will not compression ignite, octane rating is over 140, not sure what propanes is
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Old 03-18-2019, 02:23 PM   #13
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1 gallon of diesel burned produces 139000 BTUs, gasoline 124000 BTUs propane (LNG)91600 BTUs, and CNG only 900. The average price of diesel right now is $3.01 a gallon, average price of propane is $2.32. That's a 30% difference in price but a 50% increase in power with diesel over propane
The cng number is misleading, you would need to compare to LNG, cng would be pressure dependant.

That being said, they really are only useful for route trucks and must be filled every day due to short range, however they are easier to get to meet Californias clean air mandate for ports, many of them pulling containers out of the port of oakland.
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Old 03-18-2019, 05:00 PM   #14
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CNG is sold at gas that have it in gas gallon equivalent units, so when you buy 1 "gallon" of CNG, you are getting the BTU amount of 1 gallon of gas
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Old 03-19-2019, 11:08 AM   #15
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CNG is sold at gas that have it in gas gallon equivalent units, so when you buy 1 "gallon" of CNG, you are getting the BTU amount of 1 gallon of gas
Interesting...
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Old 03-19-2019, 11:28 AM   #16
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How much CNG equals a gallon of gas?
This volume of natural gas has the same energy content as one US gallon of gasoline (based on lower heating value: 900 BTU/cu foot of natural gas and 115,000 BTU/gal gasoline) One GGE of CNG pressurized to 2400psi (17MP) is 0.77 cubic foot (21.8 liters or 5.75 Gallons).
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