OT Gas/Diesel mixed fuel

Occasionally someone puts gas in one of our small diesel machines or mowers (18-23 hp range). So I usually drain the tank and I end up with a mix of say 1 or 2 gallons of gas/ 5 to 8 gallons of diesel. In the past I have dumped the mixture into our 250 gallon diesel fuel tank. My thinking was that less than 1% gas in our diesel will not hurt at all. I got that idea from the manual for my 1983 diesel VW rabbit which stated that a 10% gas mixture into the diesel was ok and maybe even preferable in the winter. But lately I have been studying diesel engine textbooks which state that gas should never be added to diesel because "it will make a powerful bomb".

I don't want to pay to have the mixture disposed up every time this happens and I'm not going to pour it into a ditch. And yes I am working on implementing a system to prevent the problem in the first place. My question is will a 1% gas mixture hurt anything?

Roland

Give it to a gasoline engine, then go fill up the tank.

A passenger car diesel doesn't have the very high compression ratio as other diesels, especially if glow plugs or airbox heaters are employed.

Or give it away on craigslist.

We would do this at the gas station when one of the kids filled up the wrong car or truck. Push it over the fill pipe in the ground, put a funnel in the neck and drain the tank. Never any issues.

I've also used gasoline cut heating oil in furnaces with above ground tanks to help with winter gelling. And added alcohol to soak up condensation, too.

Back in the days before anti waxing additives (30 years -yeah I know old fart time ) :-

1/2 gallon gas in 10 gallons diesel was the ''standard brew'' in this part of the world, it stopped waxing and never did any damage I knew of.

RMac,

You won't have any problem with that mix. As you said, and I was thinking before I read it, my Audi Diesel manual also said to use up to 10% gas in severe weather. I think I was remembering 25% but won't swear to it.

You don't make a "bomb" with gas in Diesel in a Diesel engine. Gas is 125 thou BTU. Diesel is 138,200. Gas burns quicker, tho, and it doesn't lubricate the precision fits in the injection system.

S_W_B,

I think that VW and my Audi (VW) had 23:1 compression. Big rig Diesels run about 18:1, bigger engines, I think even less.

Cheers,

George

rmcphearson said:

...lately I have been studying diesel engine textbooks which state that gas should never be added to diesel because "it will make a powerful bomb".

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I think they are referring to what is going on at the fuel tank, not within the engine. A fuel mixture with a small amount of gasoline creates a vapor mixture above it that is lean enough to explode, whilst the vapor in a tank of pure gasoline will be rich enough that it won't explode...

they are referring to the diesel motors having a higher compression ratio maybe, since the gas would likely light off before it could reach top dead center and possible cause engine damage, but like others have said at that low of % its just like running number one fuel or some kerosene or jp1 in it. At least that is how i look at it.

S_W_Bausch said:

Give it to a gasoline engine, then go fill up the tank.

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-No, definitely not. I asked here about this exact subject last summer.

Long story short, a 4:1 to 5:1 estimated gasoline/diesel mix was enough to make the gas engine run horribly and knock horrendously. Forrest suggested that even as low as 100:1 was enough to make the gas engine ping and run bad.

Apparently having the gas in the diesel engines isn't bad, and even recommended during very cold weather, but diesel in the gas is bad news. We eventually had to pump the boat dry- almost literally- replace all the filters, rebuild the carburetor and replace the spark plugs before it'd run well again.

Doc.

For the most part it will not matter to most of your small diesel engines if you mix that small amount of gas into the diesel. I expect that all of your small diesels are still using a mechanical pump for fuel injection and the older style pumps will survive this treatment.

Now, if you fuel your trucks out of this tank and you are running a newer common rail injection system then you may well experience problems.
The older VW and Audi diesels where mechanical injection systems as where the older US made engines in pickup trucks. Even as far up as 97 the 12 valve Cummins in my Dodge is still a mechanical pump.
My newer VW diesel is common rail and electronic injectors. The old systems ran at about 10,00 psi the new ones at 23 to 25,000 psi. Your prolems will come from a lack of lubrication to very tight fitting parts in the fuel injectors rather than the pump itself. 24 valve Cummins are common rail the Duramax and all the renamed International /Navistar engines in Fords are common rail electronic injector engines. And if you have an older (98 up) 24 valve cummins with a VP44 pump -well they are only a matter of time before they fail when you run really clean diesel in them...
Bryan

Virtually any gasoline in the tank of one of VW's 2009 or 2010 common rail diesels will end up requiring a nearly complete fuel system replacement to the tune of over 9k$......The high pressure pump begins to slough off metal particles and pieces very quickly. Some of the particles do get as far as the injectors. The way VW designed the system, the low pressure pump feeds the high pressure one the instant the key is turned on. Once you've done that, the destruction has begun....
If you want to read about the cost and damage, there are a number of threads over on TDIClub dot com, including one couple that the dealer misfueled their car on delivery.

Thanks for the help. All our diesels are mechanical injection pump type. I might continue to do it.

I just thought of another option. It just so happens that the other day someone busted the padlock on the gas pump trying to steal some, but they gave up because they couldn't get power to the pump. And it just so happens our diesel is not dyed. If I come across an old throw-away plastic gas can I may leave the mixture out there by mistake...

Mc,

Do as you wish.

zach123 they are referring to the diesel motors having a higher compression ratio maybe, since the gas would likely light off before it could reach top dead center and possible cause engine damage, but like others have said at that low of % its just like running number one fuel or some kerosene or jp1 in it. At least that is how i look at it.

Have you ANY idea what a Diesel IS? It is a Compression Ignition engine. It does NOT inhale a gulp of Diesel-Air, and compress it till it ignites. It COMPRESSES the air, and gets it HOT, THEN it INJECTS Diesel fuel, atomized, into that HOT air, about 6 deg before top dead center, and it ignites, hence the "ignition" part of it. IF you have gasoline in the mixture, it will STILL be injected at the proper time, BUT, you will lose power, because gasoline does not have as much heat as Diesel fuel has.

It will NOT explode, nor do I believe some of the others who say you will have a 9 grand replacement of the injection system.

"I think they are referring to what is going on at the fuel tank, not within the engine. A fuel mixture with a small amount of gasoline creates a vapor mixture above it that is lean enough to explode, whilst the vapor in a tank of pure gasoline will be rich enough that it won't explode... "
Good try, but no cigar. Where do you get the ignition? Where do you get enough O2 to mix with a closed tank?

"Long story short, a 4:1 to 5:1 estimated gasoline/diesel mix was enough to make the gas engine run horribly and knock horrendously. Forrest suggested that even as low as 100:1 was enough to make the gas engine ping and run bad."

I'll call bullshit on that. My daughter ran my 18 HP Sears GT a number of years ago. Thought she should fuel up, poured Diesel in the GASOLINE tank. That sumbitch never ran better. I have to try that, come Summer. At least the exhaust will smell better.

BRILLIANT people can come and tell us what is real, but when we listen to any reply, we get bullshit.

Cheers,

George

George: The 9 grand figure is pretty well documented as a US wide average for all those folks that have had a high pressure pump failure on a VW 2009 or 2010 common rail motor. When the hpfp fails, it has, in almost every case, spewed metal particulate from one end of the system to the other. About the only thing that doesn't get replaced is the fuel tank itself, but it still has to come out for cleaning. By the time you add up the parts, labor and the ancillary rework this causes, you get to the average price I quoted.

Just for an example, the injector pump (non high pressure) for my 2001 runs between 1200 and 2200$, depending on which of the two sizes I would need. A set of injectors will run me about 500$. These prices are from various non dealer sources. Dealership prices are going to be a lot higher. I would suspect that if we were talking about big common rail motors, we would see number just as big for similar problems

9K wouldn't surprise me on a VW. Turbo went in a friends VW golf, they did only a couple other maintenance schedule things at the same time, $3500 later, then they sold it and said never again. Another friend had the engine on his Golf also destroyed after a timing belt change done wrong at the dealer(couldn't prove it of course), putting a used/rebuilt VW engine in cost also around $3500 and that was a "deal".


Regarding diesel/gas mix, good for starting fires in winter
Now hopefully they stop mixing the 2 together though, big impossible to miss labels on everything, maybe even a custom coupling to make sure they can't get one in the other?. All that nightmare because people tend to be asleep and not paying attention at work...

gmatov, you are behind the times on diesels. The technology has changed alot in the last 15 years, as well as the fuel itself. High pressure common rail injection systems running as much as 30,000 psi don't leave a lot of room for error, nor do the latest piezoelectric injectors.

The changes in the fuel are also significant to the injection system. The 15 ppm sulfur limit of ULSD has resulted in a fuel that has very poor lubricating properties. The sulfur element did not provide lubricity, but it was attached to a molecule that did provide lubrication.

Bottom line, $9,000 full retail for a complete fuel system replacement may be unreasonable but is the going rate. The fuel injection system on a modern diesel costs more than a complete running engine did in the pre-emission era.

gmatov said:

I think that VW and my Audi (VW) had 23:1 compression. Big rig Diesels run about 18:1, bigger engines, I think even less.

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Correct. Smaller engines require higher compression ratios due to their higher heat rejection. This is particularly true of prechamber engines.

Contrary to popular belief, the goal when designing a diesel engine is to minimize compression ratio. The Carnot efficiency equation is missing some terms which, when included in the calculations, put maximum efficiency between 14:1 and 16:1. Higher ratios are only used to improve starting and to account for poor fuel quality.

Adding gas to diesel fuel lowers its cetane rating. 10% added gas might make starting a little harder in some engines but will not harm the engine.

OTOH, 10% diesel in a modern gas engine can cause damage.

Doug

Well, I'm not a petrochemical engineer, but the diesel fuel we get now is low sulfer, and the lubricity is marginal at best, not really any comparison to the stuff we got back in the '80's (that VW apparently found would work with a little gas in it). If you seize an injection pump its going to cost high hundreds to thousands to repair/replace. Not worth it over 40 bucks of gas. I wouldn't chance it even if it has been working for you, either use it in the parts washer or burn it in an old pre emissions truck. Some guys used to put maybe 1% diesel in their gas as a top oil, I've done it, never saw any difference either way.

Dale.

If all you have are older diesel engines, I say use it. We had big problems with gelling when the drivers would forget to add the fuel additive.

Long story short--I went across to the diesel doctor at the trucking company and he said to have our diesel delivered mixed with 10% regular unleaded. That is what they did from Oct. thru Apr. He told me upwards of 20% would work in extreme cold, but around 20% and higher, it starts to throw the timing off.

The trucking company ran the entire east coast, to the top of Maine, so we did what he said and never had a fuel related problem after that.

WOW, a lot of washy info.

Personally, I would not used mixed fuel in either in a modern engine. Maybe up to 10% gasoline in an old, mechanical, non-turbo diesel, but not a modern diesel.

Listen, the properties of the two fuels are totally different. We build performance engine products and have tuned the shit out of both engine types. You are asking for trouble in either situation.

Gasoline - ignition combustion, burns much faster than diesel, burn rate increases with heat/pressure, gets to a point of uncontrolled combustion (knock) if pushed too far. Timing is advanced through rpm range to increase heat in the charge and tune MCP to be around 10-12* ATDC. After 20* ATDC, any additional burned does not contribute to engine power output but may causes excessive heating of the cylinder thus our preferrence to burn fuel efficiently and quickly without running into knock.

Diesel - Diesel has an extremely LOW octane rating and will auto ignite very easily. Fuel burns slow and steady. Does not get violent in burn rate with additional heat/pressure like gasoline. Fuel is introduced to a pre-compressed cylinder and ignites as soon as it enters the cylinder. Fuel is designed to burn much longer in the cylinder thus the reason a diesel makes so much torque and also why a diesel makes so much heat. Cetane levels will dictate the burn rate of diesel fuel. The higher rpms require more cetane or faster burn rates. Diesel fuel is an oil and us used as a fuel system lubricant.

Gasoline in a diesel - Gasoline will ignite instantly when introduced to the cylinder. Will respond violently because the CR is way above the peak power CR for gasoline and will nearly explode when it goes in. Small amounts may not be noticed but will disturb the slow/steady pressure rise in the cylinder and can change when the MCP occurs thus reducing eff of the engine. Gasoline will also "cut" the diesel fuel and will damage high dollar injection pumps and can cause injector damage due to the instant, voilent combustion and will lead to injector leaking or nailing which can destroy a diesel in seconds.

Diesel in a gas engine - Diesel has a severely low octane so it will start burning way before TDC and will light the rest of the gasoline in the charge. This will kill the peak MCP and will put way more stress on the rod bearings and will excessively heat the piston. This can give the "illusion" of more power but this is only the case with low tuned engines and simply increasing timing of the engine will yield similar results but in a much safer manner. In a gas engine, we want a fast burn. Diesel burns slow in comparison and will cause excessive heat,stress, and EGTs in the engine but that is not to say they will always blow up. many low output engines are built like tanks and handle abuse better but you will not get away with this on a modern HO engine.

O2 sensing can also be affected with diesel in a gas engine due to the incomplete combustion and lack of air to complete the burn. Diesel requires a ton of air to completely burn thus why most engines today are turbod.

My question is will a 1% gas mixture hurt anything?

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1% Gas in a Diesel?

Hell NO........but do not put -any- diesel in a gas engine.

I have put up to 10% in my VW Diesel (1985 vintage) with no ill effects.
A direct injected engine may be different....

I'm guessing the small Kubota or Yanmar engines in the OP's mowers are old-style mechanical systems as well.
dk