If the HT/HS Number is the most important, then...

[HangerHarley]

.. what should it be? (This question is in regards to not using a higher viscosity, but regarding the advice given in a previous thread that increasing viscosity is not the answer nor what protects an engine, but the HT/HS strength.)

So, for example, in looking for a protective Oil, one could use a 10w30 or a 0w30 that had a very high HT/HS, like GC or perhaps an Mobil 1 0W-40?

This in regards to protecting an older engine in a HOT Climate. Without causing amazing amounts of extra wear.

 

[buster]

It's not the most important.

 

[daman]

It makes it a more robust oil yes but will lack in the fuel mileage department.

that's why in my P/U i run Mobil 1 High Mileage better HT/HS and SL add pack.

 

[Spyder7]

Its not the most important number. There is no most important. I consider all of:

cSt@100
NOACK
HTHS
Flash
Pour point
TBN

Then I look at the additive package, where possible (i.e., VOA, etc).

One score won't tell you much about the oil. You need to look at the total package to get an idea of what you're buying.

Edit: and I deliberately left some commonly tested scores out, as the numbers for the above weigh in the most in my buying decision
-Spyder

 

[Steve S]

Oil is a whole package .

 

[Tempest]

This is Bitog so everything gets taken to the nth degree on this. I don't know of anyone that has lost an engine due to lack of HTHS in their oil.

 

[dparm]

If I had to rank its importance, I would place it high up on the list. But it's the combination of HTHS, NOACK, base stock, etc. that all defines an oil.

 

[Doug Hillary]

Hi,
HangerHarley - Along with other items in the lubricant's specification the HTHS vis. is important!

The HTHS can be and indeed is a critical operational requirement for many engine families. It is a critcal item in the ACEA test protocols. It is very important to use what the Manufacturer specifies - at least the minimum they specify!

It is seen by some to only be a fuel economy parameter - this is not the case!

 

[Spyder7]

Originally Posted By: Tempest
This is Bitog so everything gets taken to the nth degree on this. I don't know of anyone that has lost an engine due to lack of HTHS in their oil.


Its an indicator of how shear resistant a given oil is. If the oil shears from say a 30 weight, to a 20 weight, lubrication failure via metal-on-metal contact may take place. Likely won't grenade the engine, but if this is a frequent and prolonged occurrence, it may shorten the life of the engine.

It still doesn't qualify as a single determining factor, since all API SM oils have to satisfy an existing standard for HTHS that is already pretty good.

As has been stated, there is no single score that will tell how good or bad an oil is. Today's oils are a complex package, and if you're willing to dig into its HTHS its just as well to dig further and look at its other key scores and additives.

Or simply buy any API SM oil of the appropriate viscosity. That's still how most people buy their oil. Or they go by a brand name and remain blissfully ignorant of its contents, other than it being motor oil to go in their engine.

-Spyder

 

[Tempest]

HTHS has to do with temporary shear in a bearing, not permanent mechanical shearing.

Lots of engines have been back spec'd to a 20 grade which provides a lower HTHS and there has yet to be mass engine failures due to this.

 

[OVERKILL]

Originally Posted By: Tempest
HTHS has to do with temporary shear in a bearing, not permanent mechanical shearing.

Lots of engines have been back spec'd to a 20 grade which provides a lower HTHS and there has yet to be mass engine failures due to this.


This is true.. But many of the Ford apps at least that were back spec'd have factory oil coolers and large sumps...... Which means cooler, thicker oil.

 

[Spyder7]

Originally Posted By: Tempest
HTHS has to do with temporary shear in a bearing, not permanent mechanical shearing.

Lots of engines have been back spec'd to a 20 grade which provides a lower HTHS and there has yet to be mass engine failures due to this.


It was a very hypothetical counterpoint to an already moot point. API SM already specifies a satisfactory HTHS, so any concern that an API SM oil will grenade an engine, based on its HTHS or any other score, is just paranoia.

-Spyder

 

[Doug Hillary]

Hi,
Tempest - The HTHS viscosity is measured under conditions similar to an operating engine. Of course this is at 150C and under shear stress conditions. These "thin film" situations typically occur in the piston ring/cylinder wall interface and in other locations. It is not all "bearing" related

 

[Tempest]

Originally Posted By: Doug Hillary
Hi,
Tempest - The HTHS viscosity is measured under conditions similar to an operating engine. Of course this is at 150C and under shear stress conditions. These "thin film" situations typically occur in the piston ring/cylinder wall interface and in other locations. It is not all "bearing" related

Thank you for the clarification.

Quote:
API SM already specifies a satisfactory HTHS, so any concern that an API SM oil will grenade an engine, based on its HTHS or any other score, is just paranoia.

Hence my first post.

 

[Doug Hillary]

Hi,
Spyder 7 - Actually the SAE's J300 classification specifies the HTHS viscosity according to the cSt range. The API's SM quality rating embraces many viscosities

 

[Spyder7]

Originally Posted By: Tempest
Originally Posted By: Doug Hillary
Hi,
Tempest - The HTHS viscosity is measured under conditions similar to an operating engine. Of course this is at 150C and under shear stress conditions. These "thin film" situations typically occur in the piston ring/cylinder wall interface and in other locations. It is not all "bearing" related

Thank you for the clarification.

Quote:
API SM already specifies a satisfactory HTHS, so any concern that an API SM oil will grenade an engine, based on its HTHS or any other score, is just paranoia.

Hence my first post.


Yeah we're both saying pretty much the same thing. I just took a more roundabout route to make the same point.

-Spyder

 

[Tom NJ]

HTHS viscosity is one factor in engine protection.

As the HTHS viscosity is reduced, the oil film becomes thinner in the hot and stressed areas of the engine, such as the bearings and cylinder walls. A thinner film means less viscous drag and results in better fuel economy. If the oil film becomes too thin, however, it may rupture, allowing metal to contact metal and resulting in increased friction, heat, and wear. The SAE sets the HTHS specifications based on extensive engine and fleet testing to assure that oils meeting the specification will have a sufficient oil film to prevent rupture and protect the engine, while maximizing fuel economy.

As the HTHS viscosity is increased, the oil film becomes thicker, creating excess frictional drag and poorer fuel economy. This can provide added protection, but only in engines that need it, such as high performance engines. Your engine builder takes the engine needs and driving conditions into account when they specify which oil specification you should use.

For most people, I would advise following the oil recommendation of your engine builder. In an old engine run under hot conditions, however, I would be inclined to use an oil with a higher HTHS viscosity, such as 3.5 - 4.0.

Tom NJ

 

[mechtech2]

I think viscosity is the most important single thing.

 

[Spyder7]

I do too, but took it as a given that he was referring to properties within a given grade of oil.

-Spyder

 

[fdcg27]

Depends.
An engine requiring a high HTHS oil, like my old BMW, should probably not be run with an oil of less than 3.5 or so, like an A3, or any BMW LL-98 or LL-01 oil.
OTOH, the Hondas and the van are happy on anything.
The Subaru?
I really don't know, but its been getting GC, an A3/BMW LL-98/LL01 oil.
Part of the lore is that Subie flat fours like a thicker oil.
Maybe so, and maybe not.
If anything, a higher HTHS oil should produce lower wear, as well as lower fuel economy.