Oil Fuel Dilution, the Russian perspective

[Sandstorm]

Fuel Dilution, being a topic of interest to me, I have had the chance to communicate with Dr. Mikhail Zlenko, PhD of Central Scientific Research Automobile and Automotive Engines Institute (NAMI) in Russia.

His response to my question of "how much oil fuel dilution do you think is too much" put me at more ease. Often time we discuss UOAs with flagged dilution levels and get concerned about those levels and it's good to see a different perspective.

 

[BornSlippy]

The job of oil in an engine is to COAT surfaces with oil. Gasoline does the EXACT opposite.

 

[ZeeOSix]

He didn't say what oil viscosity was being used in this high fuel dilution testing.

 

[bonjo]

So for short periods, the engine seems to survice but how about over a 50 or 100 k miles??

 

[ZeeOSix]

The job of oil in an engine is to COAT surfaces with oil. Gasoline does the EXACT opposite.

Fuel dilution decreases the effective oil viscosity, and therefore decreased the film thickness between moving parts. May also have an adverse effect on the AW/AF additives.

 

[JimPghPA]

In World War II it was common practice to dilute the engine oil of aircraft that were operated in Arctic conditions by adding gasoline to the oil. In fact many of those big radials could not be started in extreme cold conditions if the oil had not been properly diluted with gasoline. However, it needs to be noted that those aircraft had a huge oil tank that continuously added oil to the engine to make up for loss, which was considerable. Therefore, after a while of running the majority of the initial oil that had been diluted would have been burned out of the engine and replaced with oil from makeup supply, which although I have no actual data about, probably was not diluted or at least not as heavily diluted. Keep in mind that they did not have multi-grade oils back then.

Years ago an elderly gentleman who was an aircraft mechanic during World War II told me about how they used to dilute the oil with gasoline on those aircraft. He also told me that for the Corsairs they used to shim the wing where it met the body to adjust the angle of attack of the wing with respect to the rest of the aircraft to get the aircraft to be able to fly at a higher rate of speed than it would be able to initially fly without that shimming, but that's an off topic subject. If I remember correctly, I think we actually said was they adjusted the angle of Attack Of The Wing by removing some of the shims that were on the back part of the wing.

 

[FowVay]

Can you imagine the upper cylinder wear rate of an engine that has the lubricant diluted with a solvent at the rate of 2:1? That's just crazy to think there'd be no adverse affect.

 

[Jetronic]

Fuel Dilution, being a topic of interest to me, I have had the chance to communicate with Dr. Mikhail Zlenko, PhD of Central Scientific Research Automobile and Automotive Engines Institute (NAMI) in Russia.

His response to my question of "how much oil fuel dilution do you think is too much" put me at more ease. Often time we discuss UOAs with flagged dilution levels and get concerned about those levels and it's good to see a different perspective.

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The issue isn't at high speed but at low speed. Load does play a part, but not as much as speed. at high spped you could run a very thin oil reliably, but everytime the engine speed drops you get issues. a 30% concentration of fuel would drop the HTHS viscosity from 3.5 to about 2.6 cP, and the zddp concentration from 900ppm to 600 ppm. That's still not in imminent death territory especially at higher speeds. But start with 2.6 cP and 600 PPM and it's a different story. Drop speeds from 4-5000 rpm to 1100-1500 rpm aswell and you're in much bigger trouble

 

[Sandstorm]

In World War II it was common practice to dilute the engine oil of aircraft that were operated in Arctic conditions by adding gasoline to the oil. In fact many of those big radials could not be started in extreme cold conditions if the oil had not been properly diluted with gasoline. However, it needs to be noted that those aircraft had a huge oil tank that continuously added oil to the engine to make up for loss, which was considerable. Therefore, after a while of running the majority of the initial oil that had been diluted would have been burned out of the engine and replaced with oil from makeup supply, which although I have no actual data about, probably was not diluted or at least not as heavily diluted. Keep in mind that they did not have multi-grade oils back then.

Years ago an elderly gentleman who was an aircraft mechanic during World War II told me about how they used to dilute the oil with gasoline on those aircraft. He also told me that for the Corsairs they used to shim the wing where it met the body to adjust the angle of attack of the wing with respect to the rest of the aircraft to get the aircraft to be able to fly at a higher rate of speed than it would be able to initially fly without that shimming, but that's an off topic subject. If I remember correctly, I think we actually said was they adjusted the angle of Attack Of The Wing by removing some of the shims that were on the back part of the wing.

Pretty interesting!

 

[Stimp]

Wait'll everyone here finds out how 2-stroke gasoline engines operate.

 

[JimPghPA]

With the World War II aircraft engines and oil that had been diluted with gasoline in Antarctic conditions, those engines would have been operated at low speed when the oil was still very cold and thus very thick even with the addition of gasoline. And, they would have been throttled to a higher RPM and kept there for the entire operation of the flight.

So keeping in mind what Jetronics said, I can see where they could have gotten away with it without a problem because during the time it was run at low RPM the oil would have been much thicker and whenever they got the engine warmed up they would have been running it at higher RPM continuously and also at high load.

 

[FowVay]

In World War II it was common practice to dilute the engine oil of aircraft that were operated in Arctic conditions by adding gasoline to the oil. In fact many of those big radials could not be started in extreme cold conditions if the oil had not been properly diluted with gasoline. However, it needs to be noted that those aircraft had a huge oil tank that continuously added oil to the engine to make up for loss, which was considerable. Therefore, after a while of running the majority of the initial oil that had been diluted would have been burned out of the engine and replaced with oil from makeup supply, which although I have no actual data about, probably was not diluted or at least not as heavily diluted. Keep in mind that they did not have multi-grade oils back then.

I wasn't going to say anything but this information is erroneous. Radial engines are dry sump systems with no engine mounted sump to be diluted. There are two scavenge pumps and one feed pump on nearly every system and since the F4-U was mentioned, that is precisely how the R-2800 Pratt & Whitney 18 cylinder radial worked. If any oil was diluted then it was diluted in the oil tank that was external to the engine. The tank wasn't there to replenish any burned oil but was in fact the only source of oil for the engine.

 

[wpod]

I wasn't going to say anything but this information is erroneous. Radial engines are dry sump systems with no engine mounted sump to be diluted. There are two scavenge pumps and one feed pump on nearly every system and since the F4-U was mentioned, that is precisely how the R-2800 Pratt & Whitney 18 cylinder radial worked. If any oil was diluted then it was diluted in the oil tank that was external to the engine. The tank wasn't there to replenish any burned oil but was in fact the only source of oil for the engine.

The blow by is what dilutes and contaminates the oil with fuel moisture carbon and acids from the combustion etc.. Engine sump or remote sump.

 

[walterjay]

In World War II it was common practice to dilute the engine oil of aircraft that were operated in Arctic conditions by adding gasoline to the oil. In fact many of those big radials could not be started in extreme cold conditions if the oil had not been properly diluted with gasoline. However, it needs to be noted that those aircraft had a huge oil tank that continuously added oil to the engine to make up for loss, which was considerable. Therefore, after a while of running the majority of the initial oil that had been diluted would have been burned out of the engine and replaced with oil from makeup supply, which although I have no actual data about, probably was not diluted or at least not as heavily diluted. Keep in mind that they did not have multi-grade oils back then.

Years ago an elderly gentleman who was an aircraft mechanic during World War II told me about how they used to dilute the oil with gasoline on those aircraft. He also told me that for the Corsairs they used to shim the wing where it met the body to adjust the angle of attack of the wing with respect to the rest of the aircraft to get the aircraft to be able to fly at a higher rate of speed than it would be able to initially fly without that shimming, but that's an off topic subject. If I remember correctly, I think we actually said was they adjusted the angle of Attack Of The Wing by removing some of the shims that were on the back part of the wing.

A few years back a WW11 aircraft mechanic worked with me. He said that yes they pumped gasoline into the oil of the aircraft engines. Technically this was prohibited. When certain higher ups got word of it they began an investigation. They tore down some of those engines and found no ill effects.

 

[Brons2]

The job of oil in an engine is to COAT surfaces with oil. Gasoline does the EXACT opposite.

Coat, is not the adjective I would use. There needs to be a hydrodynamic film in the bearings to prevent wear on either opposing surface. To me "coat" describes a passive activity akin to oil contacting metal and remaining there.

 

[Owen Lucas]

He didn't say what oil viscosity was being used in this high fuel dilution testing.

Bunker fuel/ tar? /s

 

[Oliveoil2]

In World War II it was common practice to dilute the engine oil of aircraft that were operated in Arctic conditions by adding gasoline to the oil. In fact many of those big radials could not be started in extreme cold conditions if the oil had not been properly diluted with gasoline. However, it needs to be noted that those aircraft had a huge oil tank that continuously added oil to the engine to make up for loss, which was considerable. Therefore, after a while of running the majority of the initial oil that had been diluted would have been burned out of the engine and replaced with oil from makeup supply, which although I have no actual data about, probably was not diluted or at least not as heavily diluted. Keep in mind that they did not have multi-grade oils back then.

Years ago an elderly gentleman who was an aircraft mechanic during World War II told me about how they used to dilute the oil with gasoline on those aircraft. He also told me that for the Corsairs they used to shim the wing where it met the body to adjust the angle of attack of the wing with respect to the rest of the aircraft to get the aircraft to be able to fly at a higher rate of speed than it would be able to initially fly without that shimming, but that's an off topic subject. If I remember correctly, I think we actually said was they adjusted the angle of Attack Of The Wing by removing some of the shims that were on the back part of the wing.

Fascinating! Thanks

 

[ZeeOSix]

Wait'll everyone here finds out how 2-stroke gasoline engines operate.

I have rebuilt a lot of 2-stokes. The piston, rings and cylinder wears out pretty fast compared to a 4-stroke. If course, the fuel to oil ratio is much more extreme, but still a 4-stroke with 30% fuel dilution is getting up there pretty high and way above what the industry considers the fuel dilution limit.

 

[ZeeOSix]

The issue isn't at high speed but at low speed. Load does play a part, but not as much as speed. at high spped you could run a very thin oil reliably, but everytime the engine speed drops you get issues. a 30% concentration of fuel would drop the HTHS viscosity from 3.5 to about 2.6 cP, and the zddp concentration from 900ppm to 600 ppm. That's still not in imminent death territory especially at higher speeds. But start with 2.6 cP and 600 PPM and it's a different story. Drop speeds from 4-5000 rpm to 1100-1500 rpm aswell and you're in much bigger trouble

Using a viscosity mixing calculator (Widman's), a 30% fuel dilution in oil of 13.5 cSt would make the resulting viscosity 5.06 cSt. Gasoline is around 0.55 cSt at 100C.

The dynamic viscosity of gasoline would be around 0.38 cP (SG = 0.7), so using the calculator with dynamic viscosity units it would be as shown below. Since the input units are in cP, then the resulting mixture units will also be in dynamic viscosity units of cP in this case.

 

[ZeeOSix]

But start with 2.6 cP and 600 PPM and it's a different story.

Units are in cP. Oil #1 is gasoline at 100C with 0.38 cP viscosity. Gasoline is around 0.55 cP with a SP of 0.7.