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2012-2013 Boss 302 Mustang
Something to consider when the oil change topic happens here
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<blockquote data-quote="Swiss Boss" data-source="post: 14239954" data-attributes="member: 153050"><p>I can't stop reading this subject. Very interesting but pretty difficult to understand.</p><p></p><p>Found another thread on BITOG about HTHS shears.</p><p><a href="http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2501138" target="_blank">http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2501138</a></p><p></p><p>It seems that HTHS shears by half of what the viscosity shears. EX: if your oil shears by 10% then your HTHS only shears 5%</p><p></p><p>Quote from BITOG</p><p>/I tried but don't understand how the examples relate to both KV and HTHS viscosity. The latter is at one high temp of 150 C and a shear rate if 1 million per second. The former is at any temp. And a very low shear rate, driven by gravity only. Polymeric thickeners are what make the relationship between viscosity and shear rate a dependent one. The higher the shear rate, the lower the viscosity, generally. That's because the stress causes them to align in a way to reduce resistance to flow (reduce viscosity). When the stress is removed, the polymers that were not torn apart in the process go back to their original shape. That's called temporary shear. Permanent shear refers to when polymers are torn apart in the process and when the stress is removed, the KV is lower than what it was prior to the shear stress. Studies have found that when KV drops X percent from permanent shear, the HTHS viscosity drops around X/2 percent. This is because the polymers affect the KV much more than they do the HTHS viscosity.</p><p></p><p>The shear rate and temp. in the HTHS test were arrived at by analyzing a lot of data to find a good correlation between it and minimum oil film thicknesses in journal bearings and between piston rings and cylinder walls. I do not recall what engines were tested or what the oil temps. or load or RPMs were. To find this correlation with the HTHS test, they tried various temperatures and various shear rates. Each part of an engine causes different shear rates and temperatures, which varies by the engine type, load, oil properties, RPMs, and many other things. Yet, they ended up using one shear rate and temp. for the HTHS test. It does NOT completely replicate what oil experiences in every part of a hot engine; for example, oil on cylinder walls near TDC and BDC sees low shear rates because the piston speeds are low there. Oil consumption was found to decrease when polymer-containg oils with the same HTHS viscosity as monograde oils were used and it was attributed to higher actual viscosity of the multigrade oils on the cylinder walls. The HTHS test was necessitated by oils with polymers in them becoming prevalent. Monograde oils without polymers are Newtonian fluids so the viscosity is independent of the shear rate. </p><p></p><p>Those solvents are probably Newtonian fluids and the fluid shear rates were probably always much lower than 1 million per second. Sorry if my post does not address your comments or questions./</p><p></p><p>So quick math:</p><p>According to UB excel sheet, Motorcraft 5w-50 shears about 30% (average)</p><p>Then <strong>if </strong>MC 5w-50 has a HTHS @ 3.7 (still didn't find the number)</p><p>3.7 - 15% = 3.145</p></blockquote><p></p>
[QUOTE="Swiss Boss, post: 14239954, member: 153050"] I can't stop reading this subject. Very interesting but pretty difficult to understand. Found another thread on BITOG about HTHS shears. [url]http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2501138[/url] It seems that HTHS shears by half of what the viscosity shears. EX: if your oil shears by 10% then your HTHS only shears 5% Quote from BITOG /I tried but don't understand how the examples relate to both KV and HTHS viscosity. The latter is at one high temp of 150 C and a shear rate if 1 million per second. The former is at any temp. And a very low shear rate, driven by gravity only. Polymeric thickeners are what make the relationship between viscosity and shear rate a dependent one. The higher the shear rate, the lower the viscosity, generally. That's because the stress causes them to align in a way to reduce resistance to flow (reduce viscosity). When the stress is removed, the polymers that were not torn apart in the process go back to their original shape. That's called temporary shear. Permanent shear refers to when polymers are torn apart in the process and when the stress is removed, the KV is lower than what it was prior to the shear stress. Studies have found that when KV drops X percent from permanent shear, the HTHS viscosity drops around X/2 percent. This is because the polymers affect the KV much more than they do the HTHS viscosity. The shear rate and temp. in the HTHS test were arrived at by analyzing a lot of data to find a good correlation between it and minimum oil film thicknesses in journal bearings and between piston rings and cylinder walls. I do not recall what engines were tested or what the oil temps. or load or RPMs were. To find this correlation with the HTHS test, they tried various temperatures and various shear rates. Each part of an engine causes different shear rates and temperatures, which varies by the engine type, load, oil properties, RPMs, and many other things. Yet, they ended up using one shear rate and temp. for the HTHS test. It does NOT completely replicate what oil experiences in every part of a hot engine; for example, oil on cylinder walls near TDC and BDC sees low shear rates because the piston speeds are low there. Oil consumption was found to decrease when polymer-containg oils with the same HTHS viscosity as monograde oils were used and it was attributed to higher actual viscosity of the multigrade oils on the cylinder walls. The HTHS test was necessitated by oils with polymers in them becoming prevalent. Monograde oils without polymers are Newtonian fluids so the viscosity is independent of the shear rate. Those solvents are probably Newtonian fluids and the fluid shear rates were probably always much lower than 1 million per second. Sorry if my post does not address your comments or questions./ So quick math: According to UB excel sheet, Motorcraft 5w-50 shears about 30% (average) Then [B]if [/B]MC 5w-50 has a HTHS @ 3.7 (still didn't find the number) 3.7 - 15% = 3.145 [/QUOTE]
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Something to consider when the oil change topic happens here
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