Viscosity at startup
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Read this article by Shell:
Deposit Formation and Control in Engine Lubrication - Mechanisms & Models
Ian Taylor, Harold Gillespie, Richard Dixon, Bob Mainwaring, Graham Smith & Steve Nattrass
Automotive Lubricants Group Shell Global Solutions (UK)
It shows that the oil film thickness at the piston rings is greater as one goes from 40 to 30 to 20 wt. oils. The opposite is true of main journal bearings. Therefore, be careful what you assume when you talk about oil film thickness. Main bearings almost never wear out whereas cams and pistons / rings do wear the most.
Here is an article that people quote that points at the importance of HTHS viscosities:
Properties of Engine Bearings Lubricated with Low HTHS Viscosity Oils, Ono et al: Presented SAE oil Congress Detroit Feb., 1998, SAE 980702:
Tests were performed using experimental paraffin mineral based oils with some SG, API rated additives. The 100 C k. viscosities were 5.6 to 10.6, HTHS was 1.8 to 3.0. Engine testing was done at 4,800 and 6,500 RPM with sump oil temperatures at 150 C and thermocouple monitored bearing temperatures at 180 C.
They concluded that the minimum oil film thickness needed to get “normal” wear was 1.4 - 1.6 micrometers. The Minimum HTHS at 150 C needed was 2.4 to 2.6. I also noted that the wear decreased with tighter bearings (less clearance) for the oils.
Whereas main bearing wear increased with the viscosity below 2.2 HTHS, the con-rod bearing showed virtually no wear at the lowest tested 1.8 oil. Of the 3 bearings types tested 2 showed minimal wear and only one was adversely affected by HTHS viscosity below 2.2.
Critical analysis:
The testing is over 8 years old now with SG, SH, SJ, SL oils by the wayside. If HTHS of 2.4 resulted in minimal wear (only in some bearings) with those experimental oils, what would the result be using today’s oils?
The test temperatures were among the most severe. What would the test show, even back then, if the sump was kept at say 120 C or 100 C? My Ferrari sump runs at 85 C under all of my driving conditions. Also, the bearing temperatures were kept high artificially, to combat the additional cooling encountered with the thinner oils. All other things kept constant, wear increases with engine temperature.
How would modern SM or SL, thin synthetic oils, perform in the same test? What would the test show if fully formulated SG oils were used instead of the experimental oils?
I thought it was a good paper but my conclusions are that thin oils today, especially synthetic oils, are not only safe, but preferred. The other article often quoted, stating that HTHS viscosities should be 3.5 or more, is 10 or 15 years old and even more outdated. The 20 wt. oils as we know them today were not even in production.
The statement that the higher the HTHS viscosity the less the wear is incorrect. It is not a linear correlation.
I have been saying that significant wear occurs during the start-up period:
Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al: This is the benchmark study:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up).
The Effects of Crankcase Oil Viscosity on Engine Friction at Low Temperatures, Cockbill et al:
By using lower viscosity oils there is less friction, improved cold weather starting, improved fuel economy, a savings of starting system components and less wear by increasing the rate of oil pressurization and flow in the upper oil galleries.
From Nick Scianna, Posted on another board, Thursday, October 18, 2001: "Film strength" refers to the amount of pressure required to force out film of oil from between two pieces of flat metal.The higher the film strength,the more protection is provided to such parts as piston rings, timing chain, cams, lifters, and rocker arms...wherever the lubricant is not under oil-system pressure.Synthetics routinely exhibit a nominal film strength of well over 3,000 psi, while petroleum oils average somewhat less than 500 psi.The result is more lubricant protection between moving parts with synthetics.The remarkable ability of synthetic oils to reduce internal operating temperatures is far too important to ignore, since high operating temperatures contribute directly to premature failure of mechanical components and gaskets and seals.Coolant (i.e. water/antifreeze) cools only the upper regions of an engine.The task of COOLING the crankshaft, main and connecting rod bearings,the timing gears and,the camshafts and its journals,and numerous other components must borne entirely by the oil.
For those who say their oil is hot because it is hot outside:
Engine Lubrication System Model for Sump Oil Temperature Prediction, Zoz et al., SAE Congress Detroit, MI 2001.
The object was to design a model to predict engine temperatures before actual engine development. They used empirical correlations and component models including Flowmaster and ORBIT mathematical models and non-referenced actual engine temperature data for dyno tested V8 SI engines. The paper’s model was of a V8 SI engine with central camshaft and push rods.
They showed that 75 percent of engine oil heat gain in wide open throttle, full load conditions, is from the piston undercrown and that 15 percent was from the main bearings. The camshaft was only 1 percent and the oil pump energy was 8 percent. They stated that the oil heat gain from piston-bore friction was not significant.
They predicted a decrease of oil temperature of 7 F by using an aluminum vs iron block. Going from an ambient engine cooling temperature of 68 F to 122 F increased the oil temperature 14 F. It was the same for full load at 2,000 or 4,000 RPM. Increasing the ambient air temperature 86 F only increased the oil by 14 F at wide open throttle.
They compared their mathematical model to real engine data. The conclusion of the study was that the test model accurately predicted oil sump temperatures. It would be useful as a preliminary design and engine evaluation tool. (Note the heat gain through the oil pump).
aehaas
Deposit Formation and Control in Engine Lubrication - Mechanisms & Models
Ian Taylor, Harold Gillespie, Richard Dixon, Bob Mainwaring, Graham Smith & Steve Nattrass
Automotive Lubricants Group Shell Global Solutions (UK)
It shows that the oil film thickness at the piston rings is greater as one goes from 40 to 30 to 20 wt. oils. The opposite is true of main journal bearings. Therefore, be careful what you assume when you talk about oil film thickness. Main bearings almost never wear out whereas cams and pistons / rings do wear the most.
Here is an article that people quote that points at the importance of HTHS viscosities:
Properties of Engine Bearings Lubricated with Low HTHS Viscosity Oils, Ono et al: Presented SAE oil Congress Detroit Feb., 1998, SAE 980702:
Tests were performed using experimental paraffin mineral based oils with some SG, API rated additives. The 100 C k. viscosities were 5.6 to 10.6, HTHS was 1.8 to 3.0. Engine testing was done at 4,800 and 6,500 RPM with sump oil temperatures at 150 C and thermocouple monitored bearing temperatures at 180 C.
They concluded that the minimum oil film thickness needed to get “normal” wear was 1.4 - 1.6 micrometers. The Minimum HTHS at 150 C needed was 2.4 to 2.6. I also noted that the wear decreased with tighter bearings (less clearance) for the oils.
Whereas main bearing wear increased with the viscosity below 2.2 HTHS, the con-rod bearing showed virtually no wear at the lowest tested 1.8 oil. Of the 3 bearings types tested 2 showed minimal wear and only one was adversely affected by HTHS viscosity below 2.2.
Critical analysis:
The testing is over 8 years old now with SG, SH, SJ, SL oils by the wayside. If HTHS of 2.4 resulted in minimal wear (only in some bearings) with those experimental oils, what would the result be using today’s oils?
The test temperatures were among the most severe. What would the test show, even back then, if the sump was kept at say 120 C or 100 C? My Ferrari sump runs at 85 C under all of my driving conditions. Also, the bearing temperatures were kept high artificially, to combat the additional cooling encountered with the thinner oils. All other things kept constant, wear increases with engine temperature.
How would modern SM or SL, thin synthetic oils, perform in the same test? What would the test show if fully formulated SG oils were used instead of the experimental oils?
I thought it was a good paper but my conclusions are that thin oils today, especially synthetic oils, are not only safe, but preferred. The other article often quoted, stating that HTHS viscosities should be 3.5 or more, is 10 or 15 years old and even more outdated. The 20 wt. oils as we know them today were not even in production.
The statement that the higher the HTHS viscosity the less the wear is incorrect. It is not a linear correlation.
I have been saying that significant wear occurs during the start-up period:
Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al: This is the benchmark study:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up).
The Effects of Crankcase Oil Viscosity on Engine Friction at Low Temperatures, Cockbill et al:
By using lower viscosity oils there is less friction, improved cold weather starting, improved fuel economy, a savings of starting system components and less wear by increasing the rate of oil pressurization and flow in the upper oil galleries.
From Nick Scianna, Posted on another board, Thursday, October 18, 2001: "Film strength" refers to the amount of pressure required to force out film of oil from between two pieces of flat metal.The higher the film strength,the more protection is provided to such parts as piston rings, timing chain, cams, lifters, and rocker arms...wherever the lubricant is not under oil-system pressure.Synthetics routinely exhibit a nominal film strength of well over 3,000 psi, while petroleum oils average somewhat less than 500 psi.The result is more lubricant protection between moving parts with synthetics.The remarkable ability of synthetic oils to reduce internal operating temperatures is far too important to ignore, since high operating temperatures contribute directly to premature failure of mechanical components and gaskets and seals.Coolant (i.e. water/antifreeze) cools only the upper regions of an engine.The task of COOLING the crankshaft, main and connecting rod bearings,the timing gears and,the camshafts and its journals,and numerous other components must borne entirely by the oil.
For those who say their oil is hot because it is hot outside:
Engine Lubrication System Model for Sump Oil Temperature Prediction, Zoz et al., SAE Congress Detroit, MI 2001.
The object was to design a model to predict engine temperatures before actual engine development. They used empirical correlations and component models including Flowmaster and ORBIT mathematical models and non-referenced actual engine temperature data for dyno tested V8 SI engines. The paper’s model was of a V8 SI engine with central camshaft and push rods.
They showed that 75 percent of engine oil heat gain in wide open throttle, full load conditions, is from the piston undercrown and that 15 percent was from the main bearings. The camshaft was only 1 percent and the oil pump energy was 8 percent. They stated that the oil heat gain from piston-bore friction was not significant.
They predicted a decrease of oil temperature of 7 F by using an aluminum vs iron block. Going from an ambient engine cooling temperature of 68 F to 122 F increased the oil temperature 14 F. It was the same for full load at 2,000 or 4,000 RPM. Increasing the ambient air temperature 86 F only increased the oil by 14 F at wide open throttle.
They compared their mathematical model to real engine data. The conclusion of the study was that the test model accurately predicted oil sump temperatures. It would be useful as a preliminary design and engine evaluation tool. (Note the heat gain through the oil pump).
aehaas
I have to partially disagree with you on this one. If we were talking dino oils, yes I'd limit how far one would want to extrapolate out. However, since the D5133-01 Gelation Index starts it's measurement at -5C or if the viscosity exceeds 400 P, I believe one can reasonably extrapolate out to about -10C or -20C for full synthetics. Mobil published viscosity curves also substatiate this method for comparison purposes.
The calculator above uses ASTM D341-93 for viscosity-temperature relation calculations. The VI calculations use the method described in the Appendix X2 of ASTM D2270-93 and use Table X2.2.
And if you still buy into any of that, there's always the home freezer test.
[ August 22, 2005, 12:24 PM: Message edited by: 427Z06 ]
I didn't say higher HTHS oils produced less wear (though I do believe it, I didn't say it). What I said was "oils w/ a higher HTHS left thicker films on surfaces." Period.
Dave
Dave
I noticed that Dr. Haas' example was in Orlando, Florida [@104F].
So does that make thick oils a Mickey Mouse solution, or just plain Goofy?
So does that make thick oils a Mickey Mouse solution, or just plain Goofy?
Dr. Hass, I'm going to give in to your idea of thinner oil and try my wife's Turbo Volvo on 5w30, down from 5w-40. I'm using Red Line and had a great uoa. But your logic is worth trying. She drives the same route every day (50 miles one way) and I'm going to check the mileage over a few thousand miles.
I am sorry, I was not trying to pick on specific people or phases, just trying to dispel some common beliefs.
I am trying to point out that viscosity is but one criteria. As another example, a mineral based oil and an ester based oil of the same viscosity will have different levels of tenacity. Just try to wipe an ester off of your workbench. It is not easy. The mineral based oil is easier to clean. This tenacity is in itself a property of a lubricant.
Also, it is a beneficial property of oil to thin when at higher RPM and temperature and load. The oil can act as a solid if too thick and result in chunks of metal release from bearings. Ergo thicker is not necessarily better, it is just thicker.
Again, to all - You need to use the oil viscosity that works best for your situation. To understand your situation you need to know things as - oil is not over heated because the a/c is on in Florida.
'Not sure about the Castrol "startup" oil but they do define the start up period as the first 15 minutes of engine operation, not the first 5 or 15 seconds as some people define it.
aehaas
Dr. Haas, how does a thinner oil (such as a 5W-20) compare with a thicker oil (a 5w30) when it comes to protecting a camshaft and lifters in a pushrod, flat-tappet engine?
I don't know much about Ferraris, but I suspect they don't use flat-tappet cams.
Can I safely run a 5W-20 oil in a flat tappet cam, pushrod V8? I am intrigued with the concept of using such an oil in a situation where most trips are short, which is my situation.
I don't know much about Ferraris, but I suspect they don't use flat-tappet cams.
Can I safely run a 5W-20 oil in a flat tappet cam, pushrod V8? I am intrigued with the concept of using such an oil in a situation where most trips are short, which is my situation.
If the engine was designed to run a 40 wt oil at high load and RPM then it can run a 20 wt at low load and RPM regardless. A 40 wt at 240 F is thinner than a 20 wt at 180 F and my Ferrari oil temperature is 180 - 185 F no matter what I can do to the car. At this temperature my 20 wt oil is as thick or thicker than a 40 wt oil but the parts are cooler therefore less wear and tear. Some people say they get more gas mileage with a thicker oil. This would explain that. The car running the 40 wt oil has more internal friction and runs hotter with a resultant thinner acting oil. You have to keep in mind that oil does not have a viscosity by itself. It is totally temperature dependent.
For short stop and go trips a 10 wt. oil with the current additives should be good enough. If there was a fully formulated 10 wt. oil I would try it in my Ferrari.
aehaas
For short stop and go trips a 10 wt. oil with the current additives should be good enough. If there was a fully formulated 10 wt. oil I would try it in my Ferrari.
aehaas
Thanks for your reply!
I noticed that and do not know what to make of it.
aehaas
Ali,
Start up wear is a concern but the answer may be more complex than just a viscosity choice or the Castrol view.
The ester/polar element within oils IMO holds a key to the ultimate oil and the balance with AW additives.
The highly polar RL may
Start up wear is a concern but the answer may be more complex than just a viscosity choice or the Castrol view.
The ester/polar element within oils IMO holds a key to the ultimate oil and the balance with AW additives.
The highly polar RL may
...may what? I'm dying of curiosity!
So, back to my original thought. If you live in a wasrm climate and run a 40w oil, the startup difference between a 15w40 and a 5w-40 is too small to worry about, and a 15w40 might be a bit more shear stable, making it a better choice.
Pick 3500 cSt as your cut-off viscosity. Apply your temperature, voila, question answered.
427, great chart! I wonder what the temp scale for M1 0w-20/5w-20 looks like...
The better mileage with a thicker oil comes from the sealing effect that occurs with these lubes. Less blow-by gives you more power, torque, combusion efficiency and therefore better mileage.
Not by the 2-10F higher the oil temp. is with a 5-40 over a 5-20. Common... It would take a lot more than that to thin a 5-40 to a 5-20 level...
Not by the 2-10F higher the oil temp. is with a 5-40 over a 5-20. Common... It would take a lot more than that to thin a 5-40 to a 5-20 level...
That may be true if the 5w-40 and the 15w40 were made with the same basestock and VII's, in general I cannot think of a single instance where that is the case though.
As is said, Viscosity is just one paramater, tenacity is another, HTHS is yet another. One more variable, not really a parameter as it is a determinant of other properties, is base stock. 15-40's in general are made of lower refined basestocks and may not be more shear stable than a 5-40.
Due to this 20 weights are generally more shear stable than 40 weights, but after shearing the 40 weight still ends up slightly thicker than the 20 weight at the same temp.
All things must be looked at in concert.
shoudl I add , in general, once more?
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