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Here I go again - oil temp too low

rv8ch

Well Known Member
Patron
I bit the bullet and installed some aluminum sheet to block the intake side of my oil cooler. It allowed the temps to rise from about 150°F to about 175°F, according to similar flights with similar OAT according to my savvy data.

I have seen a peak of over 180°F for the first time.

So, all good, right?

My question is - besides "getting the water out of the oil" - is there really any reason to have hot oil?
 
It was recommended to me to get oil to 100F before takeoff, anything more just heat removal. Obviously heat helps with viscosity, flow, oil pumping etc. My 2cents worth.
 
My question is - besides "getting the water out of the oil" - is there really any reason to have hot oil?

No. Once warm enough to get pressures down to a normal level, the only benefit is faster water removal. Water will be removed from the oil at 150* also. Hotter is faster, but I don't know the stats on how much faster. My speculation is that it is not as much faster as most think it is. My temps only get to 160* in the winter months. Doesn't bother me. If I did a lot of short flights, I might think differently. When I worked in the auto shop in college, you wouldn't believe the amount of gunk inside the engines of the ladies that only took short trips around town (water based sludge). Those that drove to work every day for 30 minutes had zero sludge.

Larry
 
Thanks Larry.

My Blackstone reports show zero water in the oil. I use an engine dryer, not sure if that helps with this part of the oil analysis. They recommend that water in the oil should be kept low, but I don't have any comparison info.

blackstone water in oil 20210831 clip hb-ymm.png

I wonder if the engine dryer is enough to remove combustion water. Sure seems like a cool engine is a good thing.
 
Thanks Larry.

My Blackstone reports show zero water in the oil. I use an engine dryer, not sure if that helps with this part of the oil analysis. They recommend that water in the oil should be kept low, but I don't have any comparison info.

View attachment 17999

I wonder if the engine dryer is enough to remove combustion water. Sure seems like a cool engine is a good thing.

At shutdown, the air in the engine has a lot of water vapor from combustion. That moisture will condense out as things cool down after shut down and thanks to gravity, most of this water ends up at the bottom of the oil sump untill it gets chrurned up and mixted in on the next engine run. If you use a dehydrator, I don't see how you would ever get water in the oil to begin with and therefore no worries about evaporating it out.

I don't think that an oil analysis would ever show water. Water and oil molecules simply don't bond. put a bit of oil and water in a jar and shake aggressively until mixed. Come back tomorrow and have a look. A high pressure pump can churn it all up and mix it together, but once that stops, the oil and water will eventually separate and stratify. Maybe it separates out in the sealed container and blackstone agitates it to mix the water back in before going to the Mass Spectrometer. This would make sense, as they advise to drain quickly after shutdown for the sample. Maybe this is why.

Larry
 
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This isn't an engineering proof, but Lycoming says this:

"OPERATING CONDITIONS
Average *Oil Inlet Temperature

Ambient Air Desired Maximum
Above 80°F 180°F (82°C) 245°F (118°C)
Above 60°F 180°F (82°C) 245°F (118°C)
30° to 90°F 180°F (82°C) 245°F (118°C)
0° to 70°F 170°F (77°C) 245°F (118°C)
Below 10°F 160°F (71°C) 245°F (118°C)

* - Engine oil temperature should not be below 140°F (60°C) during continuous operation.
Revised September 2007 "

I think the "0° to 70°F" is a misprint, should say 30°. Or they might mean you get to choose 180°F or 170°F. and 245°F seems mighty high to me ...

From "O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf"
 
Engine oil temp

The engine oil needs to be at least 180 degrees F on the gauge (220 F return) to burn off all the deposits and accumulated water vapor. For every pound of fuel burned in an engine, the combustion process also generates a pound of water! If engine sump temperatures rarely exceed 212 degrees (water's boiling point), the water will mix with sulfur (another combustion by-product) and create acids that can eventually damage bearings.

Good luck
 
It was recommended to me to get oil to 100F before takeoff, anything more just heat removal. Obviously heat helps with viscosity, flow, oil pumping etc. My 2cents worth.

I’ve heard this “old wives tale” from several folks who heard it from a friend who heard it from someone else.
Never, ever seen anything official, except from round motor folks. If anybody has something in print from an engine source, I sure would like to see it. Until then, another “old wives tale”!
 
I’ve heard this “old wives tale” from several folks who heard it from a friend who heard it from someone else.
Never, ever seen anything official, except from round motor folks. If anybody has something in print from an engine source, I sure would like to see it. Until then, another “old wives tale”!

Agree, however, I do wait for 100F to takeoff though because if I don't that dang Dynon lady is screaming in my ear about oil pressure. :D Although she does start screaming well before the 115psi redline (for my engine) on takeoff.
 
Oil

My understanding is that 100-115 oil pressure is only for starting and low r/m ground operations. Never an issue for me because I rarely see ambient temps below 40F and at 50F the oil pressure never goes above 100. I think the 115 is for really cold ambient temps and in that case the engine should be preheaated.
Decades ago at Oshkosh a Lycoming rep told me the engine would run to TBO with oil temp at 245.
The Reno racers, especially the F1's, run some extreme temps for both oil and CHT.
The Lycoming protocol that the engine is ok for takeoff whenever it will take full throttle without stumbling. Other Lycoming info contradicts that.
 
The engine oil needs to be at least 180 degrees F on the gauge (220 F return) to burn off all the deposits and accumulated water vapor. For every pound of fuel burned in an engine, the combustion process also generates a pound of water! If engine sump temperatures rarely exceed 212 degrees (water's boiling point), the water will mix with sulfur (another combustion by-product) and create acids that can eventually damage bearings.

First, we don't "burn off" anything in the crankcase. We do wish to convert any liquid other than oil to vapor so it can leave the crankcase via the breather. Luckily it's easy, because water and other liquids with high vapor pressure will evaporate just fine at low temperatures. Oil has a very low vapor pressure, so it mostly remains in liquid phase even at very high temperatures.

Second, boiling point is merely the temperature at which vapor pressure, a physical property of the substance, exceeds local pressure, which is highly variable. Even if boiling had anything to do with evaporation of water in a crankcase (it doesn't), a 212F boiling point is only valid at sea level, on a standard day.
 
My understanding is that 100-115 oil pressure is only for starting and low r/m ground operations. Never an issue for me because I rarely see ambient temps below 40F and at 50F the oil pressure never goes above 100. I think the 115 is for really cold ambient temps and in that case the engine should be preheaated.
Decades ago at Oshkosh a Lycoming rep told me the engine would run to TBO with oil temp at 245.
The Reno racers, especially the F1's, run some extreme temps for both oil and CHT.
The Lycoming protocol that the engine is ok for takeoff whenever it will take full throttle without stumbling. Other Lycoming info contradicts that.

Lycoming operators manual states 115 is max for "start,warm-up, taxi, and takoff".
 
This isn't an engineering proof, but Lycoming says this:

"OPERATING CONDITIONS
Average *Oil Inlet Temperature

Ambient Air Desired Maximum
Above 80°F 180°F (82°C) 245°F (118°C)
Above 60°F 180°F (82°C) 245°F (118°C)
30° to 90°F 180°F (82°C) 245°F (118°C)
0° to 70°F 170°F (77°C) 245°F (118°C)
Below 10°F 160°F (71°C) 245°F (118°C)

* - Engine oil temperature should not be below 140°F (60°C) during continuous operation.
Revised September 2007 "

I think the "0° to 70°F" is a misprint, should say 30°. Or they might mean you get to choose 180°F or 170°F. and 245°F seems mighty high to me ...

From "O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf"

Thanks Bill, so Lycoming is saying keep it over 140°F. I'm not clear on why they change the minimum temperature depending on OAT. Could be just a courtesy hint to the operator to expect lower oil temps when it's cool.

I might be reading into this what I want to hear, and that's that there is no magic minimum temperature. Make sure that the oil is warm enough to flow properly, and not so hot that it breaks down.

Aeroshell seems to be saying that the driver for the min low temp is removing water and fuel from the oil:

https://www.mcfarlaneaviation.com/media/documents/aeroshell-oil-w15w-50-tds.pdf said:
Because of the improved flow characteristics of AeroShell Oil W 15W-50, operators may observe slightly lower oil temperatures in some aircraft. On larger aircraft, the oil cooler flap will normally compensate for this change. However, in small aircraft, oil temperature could be reduced slightly. Operators should always check the oil temperature to ensure that they are in the range specified by the manufacturer. Most manufacturers recommend cruising oil temperatures between 82 to 930C (180 to 2000F). Oil temperatures significantly below this range can result in excessive water and fuel contamination in the crankcase.
 
Sit back and think about the crankcase environment. It's complex.

Water is a significant byproduct of combustion, but the vast majority of it goes out the exhaust pipe. The small amount of water introduced to the crankcase enters via blow-by, i.e. leakage past the piston rings. Leakage on the compression stroke introduces atmospheric water only, in vapor phase. Leakage on the power stroke is a hot gas. As a hot gas, the combustion byproduct water is also in vapor phase. If it remains vapor, it's going out the breather with all the other gasses.

The water vapor only changes to liquid phase when cooled. The only periods of operation capable of cooling the hot gas are just after cold start and later, after shutdown. When we discuss removing water from oil, that is the water we're talking about, not water produced when everything is at full operating temperature.

Returning to hot operation, the manufacturer's stated minimum oil temperature, in the context of water, is probably based on saturation. The quantity of water vapor supplied via blow-by is some small percentage of combustion water. The percentage would vary with leakage rate, worn engines passing more into the case and tight rings sending more of it out the exhaust pipe.

Although variable, for any given quantity of fuel burned there will be a quantity of water introduced to the case. Hot air will hold far more water than cold air. At saturation (i.e. 100% RH), air at 140F will only hold about 130 g/m^3, while 160F will hold 206 grams and 200F will hold 470 grams. Because piston ring leakage is variable across the fleet, we can't know an exact figure for the quantity of water we must maintain as vapor, but I'll bet it's less than 130 g/m^3 with good tight ring sealing. Leaky rings might require some higher temperature to keep a greater quantity in vapor phase. On the other hand, an increase in the quantity of water might not drive the temperature requirement up proportionally because more leakage would also increase breather flow, thus the grams per cubic meter might not change very much.

A few years ago I beat my wee brain pretty hard to establish a dew point for breather outflow based on combustion chemistry, and came up with 125 to 145 F. It seems to align pretty well with Lycoming's minimum oil temp recommendation.
 
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Thanks Bill, so Lycoming is saying keep it over 140°F. I'm not clear on why they change the minimum temperature depending on OAT. :

I believe it is there way of saying we want 180, but 140 will work (Dan's posts explains the differences in water production based upon cyl wall/ring condition and showcases the wide variability expected out in the field) They know that the vast majority of the fleet has no way to modulate cooler performance and it is not possible to get 180* OT on most aircraft when the OAT is 0.

Larry
 
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