VIIs & differences in 5w20, 5w30 & 10w30 oils

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Originally Posted By: OVERKILL
Originally Posted By: Joe90_guy
In theory it should all go inline with the temperature of the corresponding Cold Cranking Simulator (CCS) test which defines the minimum temperature for turning the engine crackshaft over. This reads as. for 10WXX, -25C for 5WXX, -30C for 0WXX, -35C There's another test called the Mini-Rotary Viscometer (MRV) test that also gets run on oils. This always gets run at 10C below the corresponding CCS temperature, the idea being that the oil will NOT be gellified into a waxy solid at or above this temperature.
It's 5C below the CCS temp; CCS @ -35C, MRV @ -40C smile And yes, the MRV test is designed to replicate the ability for the oil to pump and it has a much higher limit on viscosity than CCS.
Thanks OVERKILL, you planted something the other day that has finally sprouted...not a eureka moment by any stretch. You'll probably recall that I've been chasing a "high shear" Viscosity index, about since that Supertech oil product data sheet lobbed complete with an "High shear" 100 viscosity. Also, I've questioned why for a given HTHS, the uber high VIs of the Japanese OEMs seem counterproductive in that they have a high KV value for a given "level of protection" (HTHS), and seem therefore wasteful of energy when it comes to simple pumping. CCS is a cranking simulator, and has a "high shear" rate, 10^4 or thereabouts. MRV is supposed to be how the engine oil makes it to the pickup, and through the pickup tube. It's shear stress is 500-1000 times lower than CCS, so shear rates are similarly lower. And as you point out, the MRV is much larger than the CCS, about 10 times, for a 5 degree change. Got me thinking about temporary shear at high shear rates (HTHS versus KV - Harmann Index if you will), and the next obvious conclusion. The CCS and MRV give an indication of the action of polymeric VIIs at the extreme cold end of the equation. Check out these Mobil oils https://mobiloil.com/en/motor-oils/mobil-super/mobil-super-synthetic See the CCS/MRV change with VII treat rate...Big difference between the 0W20 and 5W20, and the 5W30 and 10W30. Look up some 20W20 dino sheets, and the non VIIed oils are much much closer in MRV/CCS than the polymer boosted oils...obviously a 20W20 isn't the oil for a -35C morning, but the polymers that give the 0W20 it's VI aren't helping the oil get through the pickup tube.
 

SR5

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So, correct me if I've got this wrong, you're saying the VMs that make the oil easier to crank also make it harder to pump (with cold starting)? If so, wow, I never realized that.
 
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Not quite, the viscosity index of an oil is Kinematic Viscosity, KV40 and KV100, and essentially the slope of the line between them. From the early days of multigrades, it was found that (some) oils didn't live up to their KV promise, and some clever people started researching what happens to these oils inside engines...they found that these VII polymers start to get stretched/aligned in areas of the engine where the shear rate is very high (e.g. in the loaded zone of a bearing), and developed HTHS as a measure, and started including that in J300....note that the early 0W, 5W, and 10W 40s only had a minimum HTHS of 2.9, making them about as useful as a 30 grade. Less use actually, as for similar protection, their KVs were much higher than they needed to be... I'll explain...Newtonian fluids, like straight grades produce the same viscosity at all shear rates...the viscosity of the oil as it flows to the pick-up, through the galleries, and through the bearings doesn't change. And for reference, an SAE30 will have an HTHS of around 3.5, which is the minimum (now) for 0W, 5W, and 10W 40s. Polymer thickened oils have a varying viscosity depending on shear rate. That curve on the right shows what's happening to the reference oils as they are run through the engine bearings at varying RPM...once the shear rate reaches the point that the polymers are flattened out, it maintains that viscosity...called the second Newtonian range. So you can see in the chart on the left, that the "multigrade" oil had a viscosity of 9.2cst t low shear rates, and 6.7 at high shear rates...it will flow to the pickup as 'though it's a 9.2, and protect the bearings as 'though it's a 6.7. And that's what the MRV and CCS are doing...the former is the ability of the oil to flow to the pickup, and up the suction pipe, and the latter what happens in the bearings. Here's an (old) J300 Take the 0W range, 6,200CP CCS at -35C. A Newtonian oil would be expected to roughly double the viscosity (12,400ish) going to -40C, but the standard allows it to "thicken" nearly 10 fold. IMO, as the VIIs are bolstering the low shear rate viscosities, and the standard needs to allow for that.
 

SR5

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Shannow: "I'll explain ...." Thanks for that. So a Multigrade can be considered two different Newtonian Fluids, one at Low Shear and another at High Shear rates. So the values the oil needs to meet to pass the test, should reflect if it's being measured in the first / low shear Newtonian range or in the second / high shear Newtonian range.
 

SR5

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Thinking on it more. Under low shear conditions a Multigrade is probably a non-Newtonian fluid as it's apparent viscosity depends on the actual shear experienced. It only behaves as a Newtonian fluid once a critical shear level has been achieved and it's properties (and polymers) flatten out. Still most tests would be under either low or high shear conditions and should be interpreted accordingly. Feel free to correct me or ignore me as required.
 
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I Googled your source for the graphs. Small world! This stuff was done at Esso Abingdon in the '70s. I used to work there in the '80s. I can't put faces to the researchers but I have a feeling I used to know John Tims.
 
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