HTHS and mm²/s at 100 celcius.

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Hi all.

For some time i have bin trying to decide if i shoult use a acea a5/b5(HTHS 2.9-3.5) or a a3/b4(HTHS above 3.5) but that's not my question for now.

After reading a lot of TDS I have noticed that the the change from a5/b5 to a3/b4 often happens with a mm²/s at 100c at around 10. For example, my current oil fill is European synpower FE 5w-30 witch is a5/b5, it is 9.8 at 100c the. The liqui moly special F also a5/b5 is 10.0. but the liqui moly synthoil 0-30 witch is acea a3/b4 is only 10.1.

Can we conclude that an oil with a HTHS below 3.5 Will be below 10 at 100c and an oil with an HTHS above 3.5 will be above 10 at 100c.

Are oil properties a strait curve or are it a total coincidence the things I'Ve noticed.

Thanks
Søren
 
Originally Posted By: shDK
Can we conclude that an oil with a HTHS below 3.5 Will be below 10 at 100c and an oil with an HTHS above 3.5 will be above 10 at 100c.

We can't. There are plenty of oils with 100C viscosity above 10 cSt and they're still below HT/HS of 3.5 cP. For example, Castrol Edge 5w-30 that we have here has 100C viscosity of 10.7 cSt, but meets ACEA A5.

But in general, you need an oil on the high side of 30-grade in order to have HT/HS of at least 3.5 cP. That Liqui Moly product you referenced might be one of a very few exceptions.
 
HTHSV is "dynamic" viscosity, which means it's measured in an oil film squeezed in between two fast sliding surfaces -- known as high shear.

Kinematic viscosity is different than the dynamic viscosity. It's measured for low shear.

The reason why dynamic (high-shear) viscosity is needed is because oil is not just base oil but it contains some plastic that is known as viscosity-index improver. Unlike the base oil that has viscosity independent of shear rate, this plastic drops in viscosity with increasing shear rate. That's why HTHSV is needed.

Oils rated ACEA A3/B3 or A3/B4 have HTHSV >= 3.5 cP. Their kinematic viscosities (KV @ 100 C) correspond to xW-35 or higher. Note that there is no such thing as xW-35. It's something I am making up for thicker xW-30 grades that fall in the gray area between xW-30 and xW-40.

So, you do need both KV100 and HTHSV specs. However, if HTHSV >= 3.5 cP, you are getting an xW-35 (a thick xW-30) or thicker oil.

Use the HTHSV recommendation by your manufacturer. It's more important than the KV100 spec. Also, the difference between an xW-35 (a thick xW-30) and an xW-40 oil is small and you don't have to worry too much about it.

That's all to it!
 
Originally Posted By: Gokhan
HTHSV is "dynamic" viscosity, which means it's measured in an oil film squeezed in between two fast sliding surfaces -- known as high shear.

Kinematic viscosity is different than the dynamic viscosity. It's measured for low shear.

The reason why dynamic (high-shear) viscosity is needed is because oil is not just base oil but it contains some plastic that is known as viscosity-index improver. Unlike the base oil that has viscosity independent of shear rate, this plastic drops in viscosity with increasing shear rate. That's why HTHSV is needed.

Oils rated ACEA A3/B3 or A3/B4 have HTHSV >= 3.5 cP. Their kinematic viscosities (KV @ 100 C) correspond to xW-35 or higher. Note that there is no such thing as xW-35. It's something I am making up for thicker xW-30 grades that fall in the gray area between xW-30 and xW-40.

So, you do need both KV100 and HTHSV specs. However, if HTHSV >= 3.5 cP, you are getting an xW-35 (a thick xW-30) or thicker oil.

Use the HTHSV recommendation by your manufacturer. It's more important than the KV100 spec. Also, the difference between an xW-35 (a thick xW-30) and an xW-40 oil is small and you don't have to worry too much about it.

That's all to it!


My manual advise using a a5/b5 5w-30. But you can use anything from 5w-20 Wich it is spec'ed for in the US. To a 10w-40. So my concern is if I am jeopardysing enginelife using a a5/b5. And maybe a3/b4 is better.
 
Originally Posted By: shDK
Originally Posted By: Gokhan
HTHSV is "dynamic" viscosity, which means it's measured in an oil film squeezed in between two fast sliding surfaces -- known as high shear.

Kinematic viscosity is different than the dynamic viscosity. It's measured for low shear.

The reason why dynamic (high-shear) viscosity is needed is because oil is not just base oil but it contains some plastic that is known as viscosity-index improver. Unlike the base oil that has viscosity independent of shear rate, this plastic drops in viscosity with increasing shear rate. That's why HTHSV is needed.

Oils rated ACEA A3/B3 or A3/B4 have HTHSV >= 3.5 cP. Their kinematic viscosities (KV @ 100 C) correspond to xW-35 or higher. Note that there is no such thing as xW-35. It's something I am making up for thicker xW-30 grades that fall in the gray area between xW-30 and xW-40.

So, you do need both KV100 and HTHSV specs. However, if HTHSV >= 3.5 cP, you are getting an xW-35 (a thick xW-30) or thicker oil.

Use the HTHSV recommendation by your manufacturer. It's more important than the KV100 spec. Also, the difference between an xW-35 (a thick xW-30) and an xW-40 oil is small and you don't have to worry too much about it.

That's all to it!


My manual advise using a a5/b5 5w-30. But you can use anything from 5w-20 Wich it is spec'ed for in the US. To a 10w-40. So my concern is if I am jeopardysing enginelife using a a5/b5. And maybe a3/b4 is better.

No, if your manual recommends A5/B5, your best choice is an A5/B5 5W-30 (or A5/B5 0W-30).

The only thing you will jeopardize is a huge hole in your pocket if you use ACEA A3/B4 instead of the recommended A5/B5, as the cost of fuel is astronomical in Europe and the ACEA A3/B4 oils are not fuel-efficient.

A3/B4 is only to protect the main bearings of the high-performance cars that are driven very fast. For normal driving and regular cars, you don't need this category that will probably be outdated sometime not too far in the future.
 
Originally Posted By: Gokhan

A3/B4 is only to protect the main bearings of the high-performance cars that are driven very fast. For normal driving and regular cars, you don't need this category that will probably be outdated sometime not too far in the future.

It's not driving fast per se that is the requirement of a heavier HTHSV 3.5cP oil but rather the possibility of high oil temp's which can reduce the operational viscosity to a lower than recommended level.
Also another main reason that heavier oils are spec'd for performance cars that are potentially driven fast is to offset the increased oil consumption of constant high engine rev's.

ShDK, the relationship between KV100 and HTHSV is very much dependent on the oils chemistry. High polymer levels due raise the KV100 disproportionately vs HTHSV and certain esters can have low KV100 values for a given HTHSV.
But for typical mineral, GP III and PAO based oils generally you need a KV100 of 12cSt or more for the HTHSV to be at least 3.5cP.

Regarding Synthoi 0W-30 with the KV100 of 10.1cSt that's labelled an A3/B4 oil. Lets just say I'm skeptical that's it's HTHSV is 3.5cP particularly for a 0W oil. It's not impossible but they would have to be using some fairly expensive GP IV/V blends to accomplish it. I've seen a number of oils mislabeled as A3/B4, even 20 grade oils that obviously are not.
If in doubt I'd look for what the actual HTHSV is in their PDS.

You haven't said what the car is, but if an A5/B5 5W-30 is what is recommended I certainly wouldn't be using anything heavier as there would be no lubrication benefit to doing so.
In fact if the exact same engine is spec'd for a 5W-20 in the US that's probably all you need or even a 0W-20 like M1 0W-20.
 
Originally Posted By: CATERHAM
Originally Posted By: Gokhan

A3/B4 is only to protect the main bearings of the high-performance cars that are driven very fast. For normal driving and regular cars, you don't need this category that will probably be outdated sometime not too far in the future.

It's not driving fast per se that is the requirement of a heavier HTHSV 3.5cP oil but rather the possibility of high oil temp's which can reduce the operational viscosity to a lower than recommended level.
Also another main reason that heavier oils are spec'd for performance cars that are potentially driven fast is to offset the increased oil consumption of constant high engine rev's.

ShDK, the relationship between KV100 and HTHSV is very much dependent on the oils chemistry. High polymer levels due raise the KV100 disproportionately vs HTHSV and certain esters can have low KV100 values for a given HTHSV.
But for typical mineral, GP III and PAO based oils generally you need a KV100 of 12cSt or more for the HTHSV to be at least 3.5cP.

Regarding Synthoi 0W-30 with the KV100 of 10.1cSt that's labelled an A3/B4 oil. Lets just say I'm skeptical that's it's HTHSV is 3.5cP particularly for a 0W oil. It's not impossible but they would have to be using some fairly expensive GP IV/V blends to accomplish it. I've seen a number of oils mislabeled as A3/B4, even 20 grade oils that obviously are not.
If in doubt I'd look for what the actual HTHSV is in their PDS.

You haven't said what the car is, but if an A5/B5 5W-30 is what is recommended I certainly wouldn't be using anything heavier as there would be no lubrication benefit to doing so.
In fact if the exact same engine is spec'd for a 5W-20 in the US that's probably all you need or even a 0W-20 like M1 0W-20.


Thanks for a very good answer.

Here both the liqui moly synthoil and the valvoline synpower is real group 4 syn oil as far as I am informed.

The car is a 2008 Mazda 6 with the 1.8 mzr petrol.
 
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