Lightest oil?

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83
Location
California
I have a couple cars that require 5w30, and realistically I'll just be using the caterham blend to get a light 0w30 since I'll have tgmo 0w20 around. But what specs do you look for in an oil analysis that tells you how thin or thick an oil is? I have seen the viscosity @ whatever degrees but I don't understand them.
 

13Tacoma

Thread starter
Messages
83
Location
California
Awesome. Thank you. Viscosity index is like a flow characteristic right? So the higher the vi, the faster the oil will flow to protect against wear especially at startup? If that is correct then would vi be the most important characteristic of the oil and then followed by how light and the add pack?
 
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43,667
Location
'Stralia
Originally Posted By: 901Memphis
There is a range you must fall into at both the 40C and 100C mark to qualify for a certain grade. Here is the chart, you are looking at the left side for motor oil.
There's no 40C requirement for engine oils, the ISO oils are rated at 40C, the engine oils only at 100C and cold cranking type performance...no biggie, but 20 has been narrowed, and has a slight overlap with the new 16, and the table also shows gear oil viscosities as if they follow on from the engine oil series, which they don't.
 
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43,667
Location
'Stralia
Originally Posted By: 13Tacoma
Awesome. Thank you. Viscosity index is like a flow characteristic right? So the higher the vi, the faster the oil will flow to protect against wear especially at startup? If that is correct then would vi be the most important characteristic of the oil and then followed by how light and the add pack?
Viscosity is the resistance to flow, viscosity index related to how viscosity changes with temperature...a higher VI will be thicker over 100C, an thinner below 100C. Viscosity is what protects your engine, VI doesn't as two oils with same VI can have wildly different viscosities. If you get an oil analysis, they will give you the kinematic viscosity at 100C, which is useful, but you can get pretty close blending using the mixing calculator here What you really want to be chasing is the ideal HTHS for your application, as it's representative of the actual viscosity in the bearings at high RPM. See table two here TGMO is assumed to have an HTHS of 2.6, it's not published, just guessed at (some may say educated)...using the other oil that you wish to use, you can use the blending calculator to see what you end up with...minimum for a 30 grade is 2.9 HTHS, and around this HTHS should be your target if you want a "thin" 30...naturally occuring 30s without VII range up to and over 3.5 on that measure. Higher HTHS will correlate to higher film thicknesses.
 
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1,019
Location
Va
Originally Posted By: Shannow
... Viscosity is what protects your engine, VI doesn't as two oils with same VI can have wildly different viscosities. ... What you really want to be chasing is the ideal HTHS for your application, as it's representative of the actual viscosity in the bearings at high RPM. ...
I really wish this forum had a thanks button. Thank you for two of the best written sentences I've read on here for days.
 
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Messages
10,146
Location
Burlington, Ontario, Canada
Hi 13Tacoma, Just go with an approximate 60/40 ratio of TGMO and M1 0W-40. This will give you a 0W-30 with the HTHSV of a typical 5W-30 like PU but it will be lighter on start-up than all 5W-20s and most OTC 0W-20s in your climate.
 
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6,388
Location
Washington St.
I disagree with much of what Dr. Ali E. Haas, M.D., the cosmetic plastic surgeon, has written about oils. Don't worry about cold flow, especially in moderate climates like California. Any oil that meets the specs in your owner's manual will flow fine. The viscosity index is the relative change in viscosity between 40°C and 100°C. http://en.wikipedia.org/wiki/Viscosity_index A higher VI gives less thinning when hot and less thickening when cold, but all modern oils that meet your owner's manual specs will be fine. If you lived in a place with frigid winters, the thickening when cold matters more. If you live in Death Valley, the thinning when hot matters more. One of the specs in each petroleum base oil group includes viscosity index ranges, so a synthetic oil, even a (faux) syn made from Group III base oil has a higher VI. Other things remaining equal, the film thickness of the oil relates to the viscosity. A higher viscosity oil has a stronger film thickness to keep parts from touching in the engine. Other things never remain equal, and the engine designers test and test; you can trust their recommendations.
 
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40,710
Location
Great Lakes
Originally Posted By: CATERHAM
You didn't need to join BITOG to figure that one out.
Sometimes it takes a bit of time and reading to come to the conclusion that we really aren't smarter than the engine's manufacturer.
 
Messages
10,146
Location
Burlington, Ontario, Canada
Originally Posted By: Quattro Pete
Originally Posted By: CATERHAM
You didn't need to join BITOG to figure that one out.
Sometimes it takes a bit of time and reading to come to the conclusion that we really aren't smarter than the engine's manufacturer.
And some of us learn a manufacturer's other engine specifications are a more precise way of choosing or optimizing an oil's viscosity specifically to one's own application. The recommended oil grade is just the starting point in lieu of no other information.
 
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