Understanding why different viscosities are recommended?

Originally Posted by BigShug681

They don't for the most part, the oil in these trucks sees pressures of around 3000psi and it's rammed through a hole the size of the tip of a pen, anything heavier than a 30w gets reformulated into a 30w


Any UOA to back this up?
 
Originally Posted by kschachn
Then the brand of 30 grade you're using must be more of a monograde.

That example was from running a 5w40, for whatever reason the 6.0 shears anything above a 30 grade into a 30 grade very quickly and then almost holds steady at a 30 grade
 
Originally Posted by gathermewool
Originally Posted by BigShug681

They don't for the most part, the oil in these trucks sees pressures of around 3000psi and it's rammed through a hole the size of the tip of a pen, anything heavier than a 30w gets reformulated into a 30w


Any UOA to back this up?

I'll dig them up for you
 
Here's an older one from a few years ago

510867D4-7A55-4C14-914F-D5DAF5333132.jpeg
 
"They don't for the most part, the oil in these trucks sees pressures of around 3000psi and it's rammed through a hole the size of the tip of a pen, anything heavier than a 30w gets reformulated into a 30w"




Im not a mechanic but 3000 psi sounds way too high. 30psi?
 
Pim, HPOP pressures are generally in the ~3k psi range at full throttle, and usually somewhere between 1800-2000 at idle. I think under 1800 you start getting the wonky idle. I can't remember exactly because it's been a couple years since I messed with PSDs.

HPOP= high pressure oil pump
 
I'm asking for XW-30 UOA, showing that it stays anywhere close to 12cSt, like you just showed in your 15W-40 UOA.
 
Originally Posted by SubieRubyRoo
Pim, HPOP pressures are generally in the ~3k psi range at full throttle, and usually somewhere between 1800-2000 at idle. I think under 1800 you start getting the wonky idle. I can't remember exactly because it's been a couple years since I messed with PSDs.

HPOP= high pressure oil pump



ðŸ‘ðŸ»ðŸ‘ðŸ»
 
That's barely into the 30 range and not unusual after 5000 miles. I looked up typical value in the spec sheet, and it said over 15 cSt. Doesn't sound unusual, but it doesn't sound as if it sheared down quickly and stayed where it was.
 
Originally Posted by PimTac
"They don't for the most part, the oil in these trucks sees pressures of around 3000psi and it's rammed through a hole the size of the tip of a pen, anything heavier than a 30w gets reformulated into a 30w"




Im not a mechanic but 3000 psi sounds way too high. 30psi?

Not in the entire engine but at the HPOP I've seen readings close too 3500psi under a WOT run
 
Originally Posted by BigShug681
Here's an older one from a few years ago


Is this the oil you used? https://www.amsoil.com/shop/by-prod...nthetic-diesel-oil-15w-40/?code=DMEQT-EA

It's listed kinematic visc at 100C is 15.6cSt (higher end of the 40 weight category), so it is down to 12.34 (high end of the 30 weight category) after 5200 miles.

That is surprising - it was sounding like oils with a large viscosity spread (5w40, 0w40) would consist of a lower grade viscosity oil then have added viscosity improvers to get it up to the 40 weight at temp. It would stand to reason that if the viscosity improvers get sheared, destroyed, however you want to call it with the high pressures (500-3000psi) then the oil would end up being thin. However, the oil you used was a 15w40, which I would expect to have a thicker base stock viscosity grade compared to a 5W40 or 0W40.

Not sure what to make of that info.

Do you have a UOA from a 10W30 that has similar miles on it? It would be interesting to see how the 100C viscosity held up.
 
Originally Posted by jrh
Originally Posted by BigShug681
Here's an older one from a few years ago


Is this the oil you used? https://www.amsoil.com/shop/by-prod...nthetic-diesel-oil-15w-40/?code=DMEQT-EA

It's listed kinematic visc at 100C is 15.6cSt (higher end of the 40 weight category), so it is down to 12.34 (high end of the 30 weight category) after 5200 miles.

That is surprising - it was sounding like oils with a large viscosity spread (5w40, 0w40) would consist of a lower grade viscosity oil then have added viscosity improvers to get it up to the 40 weight at temp. It would stand to reason that if the viscosity improvers get sheared, destroyed, however you want to call it with the high pressures (500-3000psi) then the oil would end up being thin. However, the oil you used was a 15w40, which I would expect to have a thicker base stock viscosity grade compared to a 5W40 or 0W40.

Not sure what to make of that info.

Do you have a UOA from a 10W30 that has similar miles on it? It would be interesting to see how the 100C viscosity held up.

I am currently running Amsoil's 10w30/SAE 30 I'm about 2000k miles away from my first UOA
 
Well that answers my questions about shear stability since it is a monograde oil (with multi-vis properties due to the base stock). There's nothing to shear.

Any observed viscosity deviation would be due to dilution.
 
Originally Posted by kschachn
Well that answers my questions about shear stability since it is a monograde oil (with multi-vis properties due to the base stock). There's nothing to shear.

Any observed viscosity deviation would be due to dilution.

Don't base oils shear down to some degree? And possibly thicken? That was supposedly the trick Mobil used on an older form of Mobil 1 0W-40. I always wondered how it could be considered "Energy Conserving".
 
Originally Posted by y_p_w
Don't base oils shear down to some degree?

I don't see how they could, the average molecular diameter of a typical PAO or hydrocarbon molecule is truly tiny compared to the million+ molecular weight of a VII polymer.

I once worked on carbon black dispersion in solvent and polymer mixtures, that used a ball mill to disperse the carbon black. Inside a ball mill there are massively high shear and impact forces which did in fact break apart the carbon agglomerates (and even some of the polymer chains) but it never affected the much smaller solvent molecules. The solvent we used would have been relatively similar in chain length to engine oils.
 
Originally Posted by kschachn
Well that answers my questions about shear stability since it is a monograde oil (with multi-vis properties due to the base stock). There's nothing to shear.

Any observed viscosity deviation would be due to dilution.

That's the exact reason I switched too the 10w30/SAE30. Although a lot of people in the 6.0 groups see very little loss in Viscosity by using other 10w30s
 
Originally Posted by jrh

Something I've always wondered was why do manufacturers recommend different high temp (say 5w30 or 5w40) weights for their vehicles.


W represents winter and not weight. The number after the ‘w' represents the thickness of the oil in normal or warmer temperatures.
 
Originally Posted by BigShug681
Originally Posted by jrh
Originally Posted by BigShug681
Here's an older one from a few years ago


Is this the oil you used? https://www.amsoil.com/shop/by-prod...nthetic-diesel-oil-15w-40/?code=DMEQT-EA

It's listed kinematic visc at 100C is 15.6cSt (higher end of the 40 weight category), so it is down to 12.34 (high end of the 30 weight category) after 5200 miles.

That is surprising - it was sounding like oils with a large viscosity spread (5w40, 0w40) would consist of a lower grade viscosity oil then have added viscosity improvers to get it up to the 40 weight at temp. It would stand to reason that if the viscosity improvers get sheared, destroyed, however you want to call it with the high pressures (500-3000psi) then the oil would end up being thin. However, the oil you used was a 15w40, which I would expect to have a thicker base stock viscosity grade compared to a 5W40 or 0W40.

Not sure what to make of that info.

Do you have a UOA from a 10W30 that has similar miles on it? It would be interesting to see how the 100C viscosity held up.

I am currently running Amsoil's 10w30/SAE 30 I'm about 2000k miles away from my first UOA





Testing out amsoil on their long change intervals?
 
Originally Posted by PimTac
Originally Posted by BigShug681
Originally Posted by jrh
Originally Posted by BigShug681
Here's an older one from a few years ago


Is this the oil you used? https://www.amsoil.com/shop/by-prod...nthetic-diesel-oil-15w-40/?code=DMEQT-EA

It's listed kinematic visc at 100C is 15.6cSt (higher end of the 40 weight category), so it is down to 12.34 (high end of the 30 weight category) after 5200 miles.

That is surprising - it was sounding like oils with a large viscosity spread (5w40, 0w40) would consist of a lower grade viscosity oil then have added viscosity improvers to get it up to the 40 weight at temp. It would stand to reason that if the viscosity improvers get sheared, destroyed, however you want to call it with the high pressures (500-3000psi) then the oil would end up being thin. However, the oil you used was a 15w40, which I would expect to have a thicker base stock viscosity grade compared to a 5W40 or 0W40.

Not sure what to make of that info.

Do you have a UOA from a 10W30 that has similar miles on it? It would be interesting to see how the 100C viscosity held up.

I am currently running Amsoil's 10w30/SAE 30 I'm about 2000k miles away from my first UOA





Testing out amsoil on their long change intervals?

Yes, I've so far been able to extend my interval from 5k miles to 15k but I plan on making a few changes to possibly push it further once I install a bypass filter setup
 
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