I thought there'd be a standard but looking at Molygen 5w40 vs 5w50 I was perplexed. The 5w40 seems pretty light and says a HTHS of 3.5 which barely makes BMW LL01 spec but then the 5w50 shows 3.7 which seems super light. Redline 5w30 is 3.7. QS Euro 5w30 is 3.88. So how can they call an oil a 5w50 if it's a HTHS of 3.7? Is there a standardization I'm missing?
How is HTHS measured?
- Thread starter FlyingTexan
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HT/HS is a dynamic viscosity. It is measured at 150ºC. You can research the difference between dynamic and kinematic viscosity at your leisure.
The SAE J300 specifies that the XW-50 have a minimum HT/HS viscosity of 3.7cP. A 5W-50 can be called a 5W-50 with a HT/HS of 3.7. It's legitimate.
The SAE J300 specifies that the XW-50 have a minimum HT/HS viscosity of 3.7cP. A 5W-50 can be called a 5W-50 with a HT/HS of 3.7. It's legitimate.
dnewton3
Staff member
The issue is that many folks confuse the grade of oil with the topic of HTHS. They are perhaps best explained in that they are related, but not the same.
Grade is a value to describe the viscosity of a fluid at a specific temp. Typically the API, ISO, etc set a standard for each "grade". The viscosity in that grade is not a fixed value, but rather a range of acceptability. When you look at a 30 grade of API rating, it can have a cSt value from roughly 10.0 to 13.0 and still be a "30 grade". Further, it is not unheard of to find a "thick" 20 grade be essentially similar in viscosity to a "thin" 30 grade, for example.
HTHS is described by FowVay above. I'm sure others will also chime in with greater detail. Generally, as the lubes get hotter they degrade over time and the viscosity changes; the lubes with a higher HTHS rating will retain their viscosity more so than a lube with a lower HTHS rating, when looking at two oils of the same "grade".
See the info and the chart in this article:
https://bobistheoilguy.com/putting-the-simple-back-into-viscosity/
Grade is a value to describe the viscosity of a fluid at a specific temp. Typically the API, ISO, etc set a standard for each "grade". The viscosity in that grade is not a fixed value, but rather a range of acceptability. When you look at a 30 grade of API rating, it can have a cSt value from roughly 10.0 to 13.0 and still be a "30 grade". Further, it is not unheard of to find a "thick" 20 grade be essentially similar in viscosity to a "thin" 30 grade, for example.
HTHS is described by FowVay above. I'm sure others will also chime in with greater detail. Generally, as the lubes get hotter they degrade over time and the viscosity changes; the lubes with a higher HTHS rating will retain their viscosity more so than a lube with a lower HTHS rating, when looking at two oils of the same "grade".
See the info and the chart in this article:
https://bobistheoilguy.com/putting-the-simple-back-into-viscosity/
Iirc these 5W50 has a ton of VII in it to meet the 50 grade, so at 150C and high shear conditions, the polymers undergo temporary shear thats why you get 3.7cP. Some blenders build in temporary shear so that their oils will give good fuel economy.
Because the LM is only showing the spec min (3.5). It's likely higher. The Molygen oils are "recommended for" so no actual approvals so keep that in mind. If you look at the Leichtlauf High Tech 5W40 that has all the actual approvals you'll see 3.5 as well...again...really means "at least 3.5 but we aren't sharing the actual value." Remember that in terms of viscosity most of these Euro 40s are low w/r to the 40 grade viscosity range. The HPL Euro 5W40 has an HTHS > 4. Does any of this matter for street-driven cars beyond nitpicky discussions here? No.
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Interestingly SAE 40 has two different HTHS limits. For SAE 0W-40, 5W-40 and 10W-40, the HTHS limit is 3.5, whereas the limit is 3.7 for SAE 40, 15W-40, 20W-40 and 25W-40.
https://www.stle.org/files/TLTArchives/2023/04_April/Lubrication_Fundamentals.aspx
On the Molygen 5W50, also keep in mind that is not intented as a Euro-style oil w/r to approvals (even if they are just "recommended"). I'd use the 5W40 version in a Euro car (and I have!). It's plenty of oil for street use and I've even tracked my VW with that oil (added MoS2 for max moly!). It doesn't seem to stay in grade as well as other Euro 40s I've used/tested and that makes sense as it's not their "flagship" product; Leichtlauf High Tech 5W40 is for the Euro oil with all the standard approvals, I tracked that oil as well and it maintained grade better in my results.
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Yes like Castrol and others do on some (most? all?) of their PDS.
Patman
Staff member
I can’t imagine ever running a 5w50 oil, that would be a problem for me if I ever had a Ford Focus RS since that’s what they recommend. I would most likely run one of the higher HTHS 5w40s instead.
RS recommended 5W50? Interesting.
Patman
Staff member
And I believe other Ford vehicles that have similar versions of that engine don’t specify 5w50
It's b/c that one is "tuned to the moon" I suspect and a higher performance variant. My son wants one so bad, when he graduates college this year maybe he'll be able to find a non-clapped out one at this point. They had some issues as I recall...head gasket I believe. I see them at the track events sometimes.
Patman
Staff member
That 2.3 ecoboost is also tuned to the same 350 hp in the newer Mustangs though and I don’t think they come with 5w50.
Hopefully your son can find a good RS, I see a lot of them up here all the time and even some very low mileage ones in the Auto Trader occasionally (there was one last year with only 5000km on it!)
I think he'll find his free 2013 Focus SE 5 spd is free and therefore free. HAHAHAHA. He will want something else but I suspect graduating/getting a "real" job will be the focus (no pun intended) for a while....at some point I hope he gets what he wants. Those cars are getting older now and by the time he can afford one not sure what will be around that isn't so much $$ a newer car like a MK8 GTI would make more sense.
SammyChevelleTypeS3
$50 site donor 2023
I really feel for all young drivers when they first find out todays wild costs of plain old automobile insurance! Yikes.
Patman
Staff member
My son would not have been able to afford the insurance on his 2002 WRX when he first got it at age 16 if he was still living in Brampton Ontario (which has the highest rates in Ontario) but he was lucky that his mom moved up to Orangeville, which has some of the lowest rates in Ontario (probably half the cost)
4WD
$50 site donor 2025
My favorite is that first paycheck - what the heck is FICA ?
It's why I have my son on my insurance and he pays for his car through us as him getting that same coverage on his own is crazy expensive. Insurance prices have gone mad.
4WD
$50 site donor 2025
Here is a stout 40
He knows. Alone on his '13 Focus with liability/comp only it's about $
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