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Oil Temperature vs Volatility #5041869 03/13/19 06:23 PM
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RDY4WAR Offline OP
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Hypothetical scenario. I have no real world testing on this.

Let's say Engine A has a typical operating oil temperature of 210-225*F. Let's say this engine has evaporative oil consumption (through the PCV system) at the rate of 1 quart per 5,000 miles.

We add an oil cooler and thermostat that now keeps the typical operating oil temperature at 175-190*F.

Would it be a reasonable assumption to say the evaporative oil consumption (volatility) would decrease with the decrease in oil temperature? If not, why?


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5041887 03/13/19 06:45 PM
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Logically it makes sense that higher temps would cause more evaporation.


I use the overseas manual to choose my oil viscosity.

Using AMSOIL

Hers: 2008 Jeep Liberty 149k, SS5w30/Amsoil

His: 2015 4Runner 55k, SS 5w20/Amsoil

Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5041919 03/13/19 07:20 PM
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Don't forget that oil in the ring belt is at a slightly different temperature. What's your hypothetical oil cooler going to do there?


2011 Toyota Prius now at 101K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5041940 03/13/19 07:54 PM
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That makes sense, though I wouldn't want an oil cooler for a DI engine. Need that heat to boil off the gas.


'18 Impala
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'07 Honda Accord
'09 VStar 1300
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5041943 03/13/19 07:55 PM
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This PhD thesis by Ertan Yılmaz of MIT is probably the best study on oil consumption ever, showing the contributions of evaporation (at the cylinder liners), blowby (through the PCV valve), and oil transport (past engine valves and cylinder rings) against various variables.

"Oil evaporation is mainly governed by engine liner temperature, mass transport in the gas phase, and the available time for evaporation. Increases in engine speed increase evaporation due to the enhancement of the mass transport in the gas phase and due to the increased liner temperatures. The available time for evaporation decreases per cycle as engine speed increases, which competes with the two above effects. Since the contribution of oil evaporation increases with engine speed, the effect of higher liner temperatures and increasing mass convection coefficients must have a higher impact than the lower time available for evaporation."

SOURCES AND CHARACTERISTICS OF OIL CONSUMPTION IN A SPARK-IGNITION ENGINE
https://dspace.mit.edu/bitstream/handle/1721.1/28293/55030522-MIT.pdf

There is also a shortened version of it published by SAE:

The Contribution of Different Oil-Consumption Sources to Total Oil Consumption in a Spark-Ignition Engine
ftp://ftp.astmtmc.cmu.edu/docs/gas/emissions_task_force/minutes/20060504/sae2004-01-2909.pdf

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[Linked Image]


1985 Toyota Corolla LE, 4A-LC engine, ~ 276,000 M
Mobil 1 Extended Performance 0W-20 SN PLUS (PAO-and-AN-based)
Fram Ultra XG3600 filter (full synthetic), 90430-12031 drain gasket (rubber on aluminum)
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042006 03/13/19 08:50 PM
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RDY4WAR Offline OP
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Can you define oil transport for me? What is that referring to?

EDIT: Nevermind. Reading through the articles, it seems transport is referring to oil getting past the rings and pistons and being consumed in the chambers.

Last edited by RDY4WAR; 03/13/19 09:18 PM.

"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042073 03/13/19 09:31 PM
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RDY4WAR Offline OP
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If I'm understanding those tests correctly, oil transport and cylinder wall temperature has a greater impact on oil consumption than oil pan temperature.

Given this information, what are ways to reduce transport past the rings? Would higher viscosity reduce transport? Higher or lower HTHS?


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042100 03/13/19 10:00 PM
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Gokhan Offline
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Originally Posted by RDY4WAR
If I'm understanding those tests correctly, oil transport and cylinder wall temperature has a greater impact on oil consumption than oil pan temperature.

Given this information, what are ways to reduce transport past the rings? Would higher viscosity reduce transport? Higher or lower HTHS?

That's correct regarding the temperatures but the coolant temperature is shown to directly relate to the liner temperature and load according to Figure 4-15 at Page 114 in the thesis.

The effect of the viscosity on the oil consumption by the piston rings is modeled in Section 3.3.2.2 (Page 62) and the increasing dynamic oil viscosity (HTHSV) seems to reduce the amount of oil being dragged by the blowby by the cylinder rings. However, the oil film-thickness is also there and makes it complicated.

According to Fig 4-17 on Page 116, the oil consumption is increasing with the liner temperature at small load, where the evaporation and PCV consumption should be minimal. So, it looks like the decreasing HTHSV is increasing the oil consumption by the rings.


1985 Toyota Corolla LE, 4A-LC engine, ~ 276,000 M
Mobil 1 Extended Performance 0W-20 SN PLUS (PAO-and-AN-based)
Fram Ultra XG3600 filter (full synthetic), 90430-12031 drain gasket (rubber on aluminum)
Re: Oil Temperature vs Volatility [Re: Gokhan] #5042180 03/13/19 11:27 PM
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RDY4WAR Offline OP
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Originally Posted by Gokhan
Originally Posted by RDY4WAR
If I'm understanding those tests correctly, oil transport and cylinder wall temperature has a greater impact on oil consumption than oil pan temperature.

Given this information, what are ways to reduce transport past the rings? Would higher viscosity reduce transport? Higher or lower HTHS?

That's correct regarding the temperatures but the coolant temperature is shown to directly relate to the liner temperature and load according to Figure 4-15 at Page 114 in the thesis.

The effect of the viscosity on the oil consumption by the piston rings is modeled in Section 3.3.2.2 (Page 62) and the increasing dynamic oil viscosity (HTHSV) seems to reduce the amount of oil being dragged by the blowby by the cylinder rings. However, the oil film-thickness is also there and makes it complicated.

According to Fig 4-17 on Page 116, the oil consumption is increasing with the liner temperature at small load, where the evaporation and PCV consumption should be minimal. So, it looks like the decreasing HTHSV is increasing the oil consumption by the rings.


So in any form, it seems an oil with high HTHS and low volatility is key to reduced consumption. Could this explain situations where consumption increases the longer the oil is used if the HTHS goes down from shear?


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042265 03/14/19 05:21 AM
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Originally Posted by RDY4WAR
Hypothetical scenario. I have no real world testing on this.

Let's say Engine A has a typical operating oil temperature of 210-225*F. Let's say this engine has evaporative oil consumption (through the PCV system) at the rate of 1 quart per 5,000 miles.

We add an oil cooler and thermostat that now keeps the typical operating oil temperature at 175-190*F.

Would it be a reasonable assumption to say the evaporative oil consumption (volatility) would decrease with the decrease in oil temperature? If not, why?


isn't the oil temperature MUCH higher where the moving parts and especially the cylinders are and that's where the bulk of evaporation takes place? I'm guessing keeping the pan temperature 30° lower won't make a significant diff in evaporation loss. I would try a lower Noack oil before adding an engine oil cooler just for that (consumption) purpose.

Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042346 03/14/19 07:00 AM
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Originally Posted by RDY4WAR
So in any form, it seems an oil with high HTHS and low volatility is key to reduced consumption. Could this explain situations where consumption increases the longer the oil is used if the HTHS goes down from shear?

I think many people overfill the oil sump, which gives the false impression that initially the oil consumption is a lot lower, as it takes a while for the oil level to fall to the full mark, especially if the sump widens above the full mark.

When the oil ages, HTHSV could drop due to permanent shear or increase due to base-oil oxidation -- it's hard to say.


1985 Toyota Corolla LE, 4A-LC engine, ~ 276,000 M
Mobil 1 Extended Performance 0W-20 SN PLUS (PAO-and-AN-based)
Fram Ultra XG3600 filter (full synthetic), 90430-12031 drain gasket (rubber on aluminum)
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042452 03/14/19 08:32 AM
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RDY4WAR Offline OP
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I've seen cases where oil consumption increased after switching from a GTL synthetic (PP) to a PAO/POE synthetic (RL) despite having a lower volatility and higher HTHS. It went from 1 quart every 7,500 miles to 1 quart every 6,000 miles. In such a case, where would you start looking to find the issue?


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042755 03/14/19 12:27 PM
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I could well be wrong, but I think there is an oil consumption tradeoff between engine wear vs. emissions where lower consumption would equate to lower emissions and higher consumption would equate to lower wear.

Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5042857 03/14/19 01:26 PM
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RDY4WAR Offline OP
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That explains the correlation between ester content and oil consumption. In my experience, an oil with ester will have higher consumption than an oil without ester, even with the same volatility. Has anyone else noticed this? The theory being that esters are more polar and cling to cylinder walls causing more consumption... but also providing a better film for the rings to ride on.

Last edited by RDY4WAR; 03/14/19 01:30 PM.

"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Oil Temperature vs Volatility [Re: RDY4WAR] #5043072 03/14/19 04:59 PM
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There are so many variables involved and it can't be generalized.
One oil change in one car, different seasons and different driving conditions ... you can't draw any conclusion.
I've experienced same thing (more consumption) between comparable oils (noack) after switching brands but by the next oil change, the consumption was back to normal. did the engine get used to the new oil or was it due to the other variables i mentioned above? I couldn't draw any conclusion.
Maybe the way different oil interact with seals or the way they form tribofilm, etc. can contribute to consumption ... You always here this car likes this or that oil but you can't judge by just one oil change.

Originally Posted by RDY4WAR
I've seen cases where oil consumption increased after switching from a GTL synthetic (PP) to a PAO/POE synthetic (RL) despite having a lower volatility and higher HTHS. It went from 1 quart every 7,500 miles to 1 quart every 6,000 miles. In such a case, where would you start looking to find the issue?

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