Motors running on propane

[Rich'sToys]

My 730 is also propane, but I run it almost exclusively on vapor. I've never pulled anything heavy enough to really demand full power from the engine so haven't ever needed to open up the liquid valve. I do open it occasionally just to make sure the valve never gets stuck shut or other problems with it.

I don't use mine a lot either, and could probably get away with doing that. In fact, I probably have a few times. I mainly open the liquid valve because that's what it says in the owner's manual. Then when I shut it down I close the valve and let it run till it dies.

 

[Mcrafty1]

Rate of evaporation (turning to vapor) in/from the tank comes into play. If you have run a space heater or "weed burner" (vapor draw) off a 20 lb. tank in cold temperatures, you will see the tank show frost on the outside. That is cooling from the process of the liquid turning into a gas (vapor). Flow of vapor from the tank will drop off as it chills, reducing heater output. The same hold true for an engine using propane. Using a liquid draw system with a coolant heated evaporator to convert the liquid to vapor provides for a better flow during heavier draws seen with larger engines.

A system starting on vapor and changing to liquid after a warmup would be letting the coolant warm while there is vapor flow available from the tank which will drop off as the tank cools from the withdrawal. Once the coolant has warmed some the evaporator can take over, changing the liquid to vapor.

Larger tanks are often used on vapor draw uses to give more surface area for vaporization inside the tank.

Thanks, that explains it very well, I have a 14k standby generator and the installer said I'd need a 250 gal. bullet tank to get surface area enough to get the conversion I'd need to run it...or three of the 100 gal upright tanks. that is probably the same principal and that's just a small twin cylinder engine so I can understand a somewhat bigger engine needing the heater method.

 

[buickanddeere]

I have a tractor that is setup for propane. Was originally butane. It has valves labeled liquid, or vapor. it has a water heat exchanger. I have a fork lift that runs on propane. All fuel goes through a heat exchanger to turn the liquid to a gas. I have a generator that runs on propane straight off a small tank, like a BBQ tank. I don't understand why some propane motors don't need fuel to be heated before it enters the motor. Stan

on a side note, use low ash LP motor oil

 

[m16ty]

I have a tractor that is setup for propane. Was originally butane. It has valves labeled liquid, or vapor. it has a water heat exchanger. I have a fork lift that runs on propane. All fuel goes through a heat exchanger to turn the liquid to a gas. I have a generator that runs on propane straight off a small tank, like a BBQ tank. I don't understand why some propane motors don't need fuel to be heated before it enters the motor. Stan

If it's small engine running off a grill tank it is running off vapor. Grill tanks only supply vapor, the older ones you could turn upside down to get liquid out but the newer ones have a safety valve that won't allow you to do that.

Smaller engines can run off vapor, which is why your generator doesn't have a vaporizer. Larger engines require liquid to provide enough fuel, but require a vaporizer to vaporize the fuel before it enters the carb.

Common practice on a LP tractor is to start on vapor when it's cold, and then switch to liquid after the tractor warms up. If you don't do this the fuel system can freeze up. The tractor will idle fine on vapor, and will even rev some, but won't have good power until you switch it to liquid.

I prefer LP powered things like tractors that don't get used often over gas engines. You can take a LP fueled tractor, let it sit for years, and put a hot battery on it and it will start right up like you ran it yesterday. Try that with a gas tractor. Also engine will last longer and less maintenance all around because LP doesn't go bad and doesn't gum stuff up.

On a side note, the correct term for the fuel is LP or more correctly LPG. While there is pure propane like you buy in those little bottles of propane that you use on a small torch, usually what you buy in bulk or grill tanks is mostly propane but hasn't been refined enough for it to be pure. It's common for it to have some butane and other gasses in the mix. Which is why they have to call it "liquified petroleum gas" (or LPG), because it's not pure propane.

 

[rustred]

I do not agree with the engine lasting longer on propane. Any propane engines I have seen the heads are worn right out from lack of lube. This includes the stationary engines running pump jacks in the oil field.

 

[m16ty]

I do not agree with the engine lasting longer on propane. Any propane engines I have seen the heads are worn right out from lack of lube. This includes the stationary engines running pump jacks in the oil field.

That's not been my experience, having worked on propane forklifts for over 30 years. Propane doesn't contaminate the oil like gasoline does.

Engines running in the oil field usually run 24-7 and rack up a lot of hours pretty quick. Of course in that application nothing is going to last very long before wearing out.

 

[rustred]

That is true they burn cleaner than gas. And have cleaner oil . But there is no lube in propane for the valve guides. I am a mechanic also and seen many heads with the guides worn right out. It’s a proven fact.

 

[BarnyardEngineering]

That is true they burn cleaner than gas. And have cleaner oil . But there is no lube in propane for the valve guides. I am a mechanic also and seen many heads with the guides worn right out. It’s a proven fact.

So you've seen it a couple times, that makes it a proven fact?

Gasoline does not have any lube in it for the valve guides either. The oil being pumped up to the top of the head has lube in it for the valve guides.

 

[timcasbolt]

 

[buickanddeere]

LP, NG abd DI gas engines do not have liquid gasoline to keep PCV deposits washed off the backs of the intake valve .

 

[ss55]

That is true they burn cleaner than gas. And have cleaner oil . But there is no lube in propane for the valve guides. I am a mechanic also and seen many heads with the guides worn right out. It’s a proven fact.

Running 24/7/365 is over 8000 hours per year, most gas engines need an overhaul in less hours than that. How many hours are on the heads with worn out valve guides? How does that compare to the life of a gas engine?

 

[used red MN]

LP, NG abd DI gas engines do not have liquid gasoline to keep PCV deposits washed off the backs of the intake valve .

Was PCV the intended acronym, Positive Crankcase Ventilation? Deposits on the back sides of intake valves come mainly from oil that has made its way down the guide an onto the valve stem. Never really thought about it much but even positive seal valve seals meter some amount of oil into the guide for lubrication. I would not argue that the gas droplets in the intake mixture do “wash” the back side of the valves to a degree, but very minimally I would say. The amount of oil/carbon deposits on valves from the PCV system in a healthy engine should be minimal. The amount of oil vapors that get into the intake through the PCV system is all a component of the design of the baffling in the oil/vapor separation unit and the amount of blow-by of the engine. Even the fairly small separator in a small block Chevy valve cover was fairly effective. This is proven by the fact that many of those engines could go 2000 miles and not use a quart of oil. Wasn’t mentioned here but again in an engine in good condition, exhaust valve deposits are from a mix of guide lube oil and combustion products molecularly transferred to the valve surface due to it high operating temperature.
Yes, LPG engines do require a more robust valve package due to higher combustion temperatures, particularly better exhaust valves and seats. I would guess the majority of experiences with valves that didn’t last as well in a LPG engine were in those regular gas engines that were converted to run on LPG without any valve upgrades.

 

[rustred]

propane runs hotter and dryer than gasoline, naturally this will cause more wear on the valve guides and seats. also propane heads should have sodium valves to help cool them. i know what i know from actually working on them in the dealership. seams to me like hands on experience dont count here. every time a propane vehicle came in for a valve job there was always comments on how hard propane was on heads. I'll just leave it at that.

 

[TheBartman47]

That's not been my experience, having worked on propane forklifts for over 30 years. Propane doesn't contaminate the oil like gasoline does.

Engines running in the oil field usually run 24-7 and rack up a lot of hours pretty quick. Of course in that application nothing is going to last very long before wearing out.

My family had a 1947 LP fuel John Deere model 50 that sat for 8 years after a long life working a 90 acre farm. I put a battery in it one day and it cranked right up like it had never been sleeping all that time. The LP fueled 730 I have now also sat for about 5 years or so before I bought it. It too cranked right up after putting a battery in it.

 

[John M]

SHHHHHH! Dont tell my forklifts propane wears out the valves, they might decide to go on strike. 2 of my outside lifts have over 10000 hours with nothing more than oil changes, an alternator, and a couple of houses. Our backup yard truck is propane, and its got well over 15000 on it and has never been touched, at least sine Ive been here, but of course none of our diesel yard trucks give up any trouble either.

 

[TheBartman47]

propane runs hotter and dryer than gasoline, naturally this will cause more wear on the valve guides and seats. also propane heads should have sodium valves to help cool them. i know what i know from actually working on them in the dealership. seams to me like hands on experience dont count here. every time a propane vehicle came in for a valve job there was always comments on how hard propane was on heads. I'll just leave it at that.

I would think engines originally designed specifically to run on propane would have already taken such considerations into account. Maybe gasoline engines converted to LP might have issues?

 

[m16ty]

SHHHHHH! Dont tell my forklifts propane wears out the valves, they might decide to go on strike. 2 of my outside lifts have over 10000 hours with nothing more than oil changes, an alternator, and a couple of houses. Our backup yard truck is propane, and its got well over 15000 on it and has never been touched, at least sine Ive been here, but of course none of our diesel yard trucks give up any trouble either.

We have a 1978 Cat propane forklift Dad bought used in 1984. That thing has been run for several hours at least 2-3 times a week since then. I don’t know how many hours that equals but the Continental flathead in it has never been touched since we’ve had it.

 

[buickanddeere]

My family had a 1947 LP fuel John Deere model 50 that sat for 8 years after a long life working a 90 acre farm. I put a battery in it one day and it cranked right up like it had never been sleeping all that time. The LP fueled 730 I have now also sat for about 5 years or so before I bought it. It too cranked right up after putting a battery in it.

LP 50’s were built from late 1954 model year to the end of production 1956. Earliest LP 50’s were single barrel carbs and B heads .

 

[zuhnc]

Generally purpose-built LPG engines have premium valve and seat assemblies to mitigate wear. Stellite valves and hard seats. I think the guides are standard, but some might have harder guides, I don't know for sure.

 

[Sberry]

We used to install hard valves then engines went to no lead and they seem to be fine. I yanked an oil sample from a unit I had remote, got to be close to 2k hrs and 15 years on an oil change and ran near wide open. I am intending on sending it in yet.