Can someone please explain what is a good # for Viscosity?
- Thread starter V8Blitz
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A higher VI number may be better or it could mean that a lot of viscosity index improvers have been stirred into the oil--so I ignore VI. In general a higher flash point is good, lower NOACK number is good, higher TBN is goood, lower pumping and cold crank viscosities are good, higher HTHS to a point (3.5 is a decent HTHS and anywhere from 3.0 to 4.0 is probably a reasonable range). As for 100C viscosity you first have to look at what grade you are running (10w30, 10w40, etc.), then look at the viscosity ranges on this chart. I have never given a rats tail what the 40C viscosity was. Seems to me that the 100C and 150C (HTHS) along with the cold crank and cold pump viscosities are far more important.
Also nice to have a lot of calcium (see Maxlife product tech data sheets for a decent calcium level) as calcium is good detergent, antiwear, and acid neutralizer, among other things.
[ May 15, 2005, 12:32 AM: Message edited by: TallPaul ]
Not sure, just in the back of my mind I recall something about too high of an HTHS maybe is a problem, but I don't think you will encounter an HTHS that is too high unless you plan on running something like 20w60 maybe. Would not be concerned with the high end.quote:
Originally posted by V8Blitz:
This is all very confusing, however.For instance, why is the HTHS good to be high up to a point?
Actually a lot of folks are going to say HTHS can be below 3.0 and they may well be right. There was some sort of study that supposedly showed that HTHS must be at least 2.6 or was it 2.8 and that apparently was needed to allow for 5w20 oils that typically are under 3.0 HTHS.
Here is a big long thread on HTHS that may help clarify some of the issues.
From shortly into that thread:
So it seems the issue is that it does no good to have too high of an HTHS, but apparently no harm either. Not sure what that number is though.
[ May 15, 2005, 08:51 AM: Message edited by: TallPaul ]
HTHS in law mans terms is the oil ability to resist shearing. SO the higher the number the harder it is to cut the oil into smaller dysfunctional pices. I am over simplyify here. An HTHS of 2.6 is the minimum for long term valvetrain wear and rod bearings. Some new lead matrix's are makeing this less of a problem for bearings but longterm valve train wear is still an issue. Your valvetrain wear and bearing wear in most applications drops significantly as you pass an HTHS of 2.9. It continues to fall of very sharply until you hit about 3.6 then it contines to drop off at a slower rate until you hit about 4. Once you pass an HTHS of 4 the only people that are going to see a reduceing in wear are those people severly pushing the limits of their engine. You really can not have too much HTHS as it is not an issue their is no down side to high HTHS numbers in terms of wear.
Now while HTHS is not linear to SAE viscosity it does track with viscosity for the most part. The big thing is that it tracks with the viscosity of the base stock. So if we have two identical base stock the one with more viscosity is going to have a higher HTHS. Different base stocks have different levels of shear resistance and the viscoity improvers also play a role. FOr example esters have better shear resistance then a PAO so an ester based 5W20 can have an HTHS of 3.3 while a PAO/AN based oil might be an SAE 0W30 and have an HTHS of 2.9. So we always have to compare apples to apples. If two oils of close to the same base stock make up have simalar HTHS numbers but vary different viscosity's generaly the oil with the lower SAE viscosity spread is going to be more shear resistant. A good example of this is GC 0W30 HTHS of 3.6 V.S. M1 0W40 HTHS of 3.6. Both of these oils due a good job in terms of generaly produceing low wear numbers. THe GC has never sheared while the M1 0W40 often shears and in some cases has exsaberated oil consuption issues.
The reason some people are leary of higher HTHS oils is that generaly HTHS does track with viscosity. So in order to get an HTHS above 4 you usualy have to go with a 10W40,15W40,15W50,20W50,25W70 oil in order to get above 4. You usualy give up more in HP, flow,pumpability then what you gain in wear reduction due to the law of deminishing returns. You might also consider it as a function of marginal return. Their is always going to be a sweet spot in almost any thing were you get the most bang for your buck. In general in most light duty passenger cars and trucks that sweet spot is between 3-4 with 3.6 seeming to be the most freq. and general sweet spot encountered! You can find oils from 5W20-10W40 that fall between 3.2-4 with no problem at all. So it truly is not an issue for someone to be able to find an oil that works best in their car. Most will tell you to use the lightest oil that turns in good UOA numbers for your car. This maximizes fuel saveings and will keep wear at a mangeable level.
Audi has been haveing oil related failures and is really specific about what they want. I would not use an oil in an Audi that did not havwe an HTHS of at least 3.5 personely. I belive Audi wants an HTHS of 3.6 min. but again ask some audi owners.
Now while HTHS is not linear to SAE viscosity it does track with viscosity for the most part. The big thing is that it tracks with the viscosity of the base stock. So if we have two identical base stock the one with more viscosity is going to have a higher HTHS. Different base stocks have different levels of shear resistance and the viscoity improvers also play a role. FOr example esters have better shear resistance then a PAO so an ester based 5W20 can have an HTHS of 3.3 while a PAO/AN based oil might be an SAE 0W30 and have an HTHS of 2.9. So we always have to compare apples to apples. If two oils of close to the same base stock make up have simalar HTHS numbers but vary different viscosity's generaly the oil with the lower SAE viscosity spread is going to be more shear resistant. A good example of this is GC 0W30 HTHS of 3.6 V.S. M1 0W40 HTHS of 3.6. Both of these oils due a good job in terms of generaly produceing low wear numbers. THe GC has never sheared while the M1 0W40 often shears and in some cases has exsaberated oil consuption issues.
The reason some people are leary of higher HTHS oils is that generaly HTHS does track with viscosity. So in order to get an HTHS above 4 you usualy have to go with a 10W40,15W40,15W50,20W50,25W70 oil in order to get above 4. You usualy give up more in HP, flow,pumpability then what you gain in wear reduction due to the law of deminishing returns. You might also consider it as a function of marginal return. Their is always going to be a sweet spot in almost any thing were you get the most bang for your buck. In general in most light duty passenger cars and trucks that sweet spot is between 3-4 with 3.6 seeming to be the most freq. and general sweet spot encountered! You can find oils from 5W20-10W40 that fall between 3.2-4 with no problem at all. So it truly is not an issue for someone to be able to find an oil that works best in their car. Most will tell you to use the lightest oil that turns in good UOA numbers for your car. This maximizes fuel saveings and will keep wear at a mangeable level.
Audi has been haveing oil related failures and is really specific about what they want. I would not use an oil in an Audi that did not havwe an HTHS of at least 3.5 personely. I belive Audi wants an HTHS of 3.6 min. but again ask some audi owners.
You're exactly right. Audi just published a bulletin ststing that oils for their cars must have a HTHS of at least 3.5. That is some very good info you provided. In my 4.2 I was driving very aggressively yesterday and when I checked the oil level it was low; at the top of the bottom orange piece and JUST touching the metal. I don't know if you are familiar w/ Audi dipsticks but this is usually a 1/2 to 1 qt. low. I believe my car holds 12-13qts. of oil. Could this have caused a problem?
If they are doing an oil consuption test leave it alone! They should have you come back in in 1000 miles to check the reading. Make sure they do not do anything funy to get out of warranty work. If you are 1/2-1 quart low at a 300 miles it will definately be lower then allowed by the 1000 mile mark wich is good if you are looking for warranty work!
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