Moroso Explains How Engine Temps Tamper With Oil Movement
Oil pressure and engine temps not aligning with the pressure coming from your crankcase? Moroso thinks your oil temps may have affected flow.
www.enginelabs.com
Moroso article on pressure vs. temperature
- Thread starter SubieRubyRoo
- Start date
www.enginelabs.com
dnewton3
Staff member
There are a few points which need addressing, but overall I think the article was interesting and informative ...
- The oil temp does not "double", technically. We presume it does because of the Fahrenheit scale, but in terms of true thermal energy (based on the Kelvin scale), the oil temp does not "double". Even if you used Celcius, the temp does not "double". It only doubles because it was measured in Fahrenheit. When engineers truly calculate thermal energy transfer, it's typically done in Kelvin to properly account for expansion. This is a common misunderstanding and misapplication of thermodynamic laws. In this article, the stated conditions produced the following "temp" changes. Note that I round to the nearest whole integer:
80F to 160F (exact double)
27C to 71C (more than doubles)
300K to 344K (less than doubles)
- There is validity in the topic of how the flow rate changes with the temps. But this really can't be fresh news to any of us, can it? This is why sumps are (or at least should be) sized for the varied expectations of applications. In this case, it was a racing application. But the same holds true for "normal" cars, trucks, tractors, motorcycles, etc ... There is a known volume of oil needed to account for the variance of drainback from cold to hot operational conditions. There also needs to be a min specific volume of the sump in terms of physical holding capacity so that undesirable events don't occur. Kind of like Goldie Locks; too much or too little isn't good.
- Obviously (at least to most of us), this set of data only applies to the specific oil used under those conditions. There will be a different response curve for different lubes ... 15w-40 isn't going to flow the same as 5w-20, for those stated test parameters, etc.
The article is interesting and informative, but I fear the common BITOGer is going to take that info and run with it, assuming it applies to all lubes at all times, and that's flat out wrong. It does a good job of illuminating the concept of oil flow changing with temps, but it's NOT to be considered a one-size-fits-all engineering answer.
- The oil temp does not "double", technically. We presume it does because of the Fahrenheit scale, but in terms of true thermal energy (based on the Kelvin scale), the oil temp does not "double". Even if you used Celcius, the temp does not "double". It only doubles because it was measured in Fahrenheit. When engineers truly calculate thermal energy transfer, it's typically done in Kelvin to properly account for expansion. This is a common misunderstanding and misapplication of thermodynamic laws. In this article, the stated conditions produced the following "temp" changes. Note that I round to the nearest whole integer:
80F to 160F (exact double)
27C to 71C (more than doubles)
300K to 344K (less than doubles)
- There is validity in the topic of how the flow rate changes with the temps. But this really can't be fresh news to any of us, can it? This is why sumps are (or at least should be) sized for the varied expectations of applications. In this case, it was a racing application. But the same holds true for "normal" cars, trucks, tractors, motorcycles, etc ... There is a known volume of oil needed to account for the variance of drainback from cold to hot operational conditions. There also needs to be a min specific volume of the sump in terms of physical holding capacity so that undesirable events don't occur. Kind of like Goldie Locks; too much or too little isn't good.
- Obviously (at least to most of us), this set of data only applies to the specific oil used under those conditions. There will be a different response curve for different lubes ... 15w-40 isn't going to flow the same as 5w-20, for those stated test parameters, etc.
The article is interesting and informative, but I fear the common BITOGer is going to take that info and run with it, assuming it applies to all lubes at all times, and that's flat out wrong. It does a good job of illuminating the concept of oil flow changing with temps, but it's NOT to be considered a one-size-fits-all engineering answer.
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Apologies to the board; I meant to and should have commented, I found this on Engine Labs, and while dnewton3 points out there are definitely some caveats to the article, this was definitely an angle that most people do not even consider in their daily operation.
MolaKule
Staff member
Lubricating oil Densities change with Temperature:
www.tribonet.org
www.engineeringtoolbox.com
Density of Oil - About Tribology
www.tribonet.org
Lubricating Oil - Densities vs. Temperature
Variations in lubricating oil density as function of temperatur, together with volume correction factors.
www.engineeringtoolbox.com
Wasn't this article posted before in a different thread - I made comments about their testing flaws with regard to their comment near the end of the article. This can not occur in a real engine due to how a positive displacement oil pump works in an engine oiling system. Oil flow can not increase as the viscosity decreases in a real engine. Most know that a PD oil pump will basically move the same volume per RPM regardless of oil viscosity as long as the pump is healthy and not in pressure relief. In a real engine, the oil pressure at X RPM and corresponding Y flow will go down as as the oil temperature goes up. The only way to maintain 60 PSI as the oil temperature increases is to also increase the engine RPM. And that in turn also increases the flow rate.
Their table below shows they held the RPM and pressure constant, and the oil flow increased as the oil temperature increased. That's impossible in a real engine oiling system. You would basically need an oil pump that you could control the volumetric output to keep the output at a constant 60 PSI as the oil temperature increased while keeping its speed at a constant 1250 RPM. That's only possible on a special bench test setup that doesn't represent a real engine oiling system.
Their table below shows they held the RPM and pressure constant, and the oil flow increased as the oil temperature increased. That's impossible in a real engine oiling system. You would basically need an oil pump that you could control the volumetric output to keep the output at a constant 60 PSI as the oil temperature increased while keeping its speed at a constant 1250 RPM. That's only possible on a special bench test setup that doesn't represent a real engine oiling system.
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wemay
Site Donor 2023
^^^ A well designed and healthy PD oil pump used in an engine oiling system will not have much "slip" as the output pressure increases. They are capable of basically destroying something with very high oil pressure if there wasn't a pressure relief valve to limit the maximum output pressure. A PD oil pump also has less "slip" with thicker oil as the pressure increases inside the pump. Therefore, theoretically a PD pump could be a bit less efficient at pumping (ie, output flow decreases slighty at higher pressure) as the oil becomes thinner due to using a thinner oil and/or increased oil temperature. Every oil pump will have an output flow vs RPM vs fluid viscosity performance curve. It's also possible, depending on the pump design, for the pump to cavitate at higher RPM which will impact the output pressure and flow.
