Can a high HTHS ever be detrimental to engine protection?
- Thread starter ZZman
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Reductin in power, fuel economy come to mind.
The only issue I could see is someone running the oil too long. Some people might base their OCI on what someone else has done without getting their own UOA data to determine if the oil is still fit for service. What works for some might not work for all when it comes to extending an OCI. Other than that I see no downside.
dnewton3
Staff member
HTHS essentially is the rating of a lube's ability to retain vis in extreme heat.
How in the world would a lube with high HTHS value be "detrimental to engine protection"?
As opposed to what as an alternative; a lube with low HTHS which degrades quickly?
I also disagree with your poorly defined statement that "a higher HTHS gives better wear protection". That's a very broad paint brush with which to paint. To be more specific, lubes with a high HTHS value likely will protect LONGER (extended OCIs), but in shorter OCIs they are not shown to do much different at all. Much of this would depend upon the specific application and use factors.
How in the world would a lube with high HTHS value be "detrimental to engine protection"?
As opposed to what as an alternative; a lube with low HTHS which degrades quickly?
I also disagree with your poorly defined statement that "a higher HTHS gives better wear protection". That's a very broad paint brush with which to paint. To be more specific, lubes with a high HTHS value likely will protect LONGER (extended OCIs), but in shorter OCIs they are not shown to do much different at all. Much of this would depend upon the specific application and use factors.
I thought they not only protected better but also longer. I usually do 5,000 miles oci.
I hope not! 
A loss of power/mpg. If you're having to increase viscosity to obtain that HTHS then you have added heat.
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But these don't really affect protection in a negative way just other things correct?
I wonder what the true power/mpg hit is?
Added shear heating in the bearings is a minor factor when we are talking a modest increase in HT/HS. It's not an issue. The oil is better able to withstand the heat without excessive thinning anyway.
I don't think so.
The true mpg hit depends on the difference in grade of the oils you're measure. IIRC BMW mentioned up to 3% fuel savings when moving from 3.5cP to 3.0cP. The greater the spread between HTHS and viscosity the greater the difference in mpg. There are ACEA test sequences which have a FE component (ex ACEA C2).
EDIT: It's worth noting what 3% actually looks like. If your combined MPG is 28 then adding 3% would increase that to 28.84. Not a big deal to you but it is for an automaker who sells hundreds of thousands of vehicles every year.
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In my vehicles, mpg difference is in the noise. Tends to be ever so slightly lower in the Winter and ever so slightly higher in the Summer. So if there is a change, it's a wash.
Power? My calibrated butt dyno says it's ever so slightly up.
dnewton3
Staff member
Lubes with a high HTHS valuation are going to be very important if you run very high temps for sustained periods (racing), or used in high power-dense applications (tuned turbo engines with long OCIs). You can extend the OCIs because the lube is likely to hold it's vis for a longer duration, if you interpret "better" as meaning "for a longer period before degrading".
The OPs question wasn't about efficiency or loss of power; he inquired about higher HTHS being "detrimental to engine protection". Further, he confined his initial query to a "normally used vehicle"; the inference taken that this is not about a high-performance application (race cars; super-charged Hemi Challenger; turbo'd Mustang running 30 psi boost, etc ...).
There's no reasonable way to conceive that a quality HTHS lube is going to harm an engine in terms of wear in the inferred application.
The OPs question wasn't about efficiency or loss of power; he inquired about higher HTHS being "detrimental to engine protection". Further, he confined his initial query to a "normally used vehicle"; the inference taken that this is not about a high-performance application (race cars; super-charged Hemi Challenger; turbo'd Mustang running 30 psi boost, etc ...).
There's no reasonable way to conceive that a quality HTHS lube is going to harm an engine in terms of wear in the inferred application.
BrendanC
$100 site donor 2024
i stepped a honda K24 from a 5w-20 with an average HTHS value of ~2.7cP to HPL's 5w-40 with a HTHS value of 4.248. so far the engine is much quieter and hasn't taken a hit to fuel economy (already have 1600 miles on the oil)
Our Hyundai has the 2.0 turbo GDI engine. Known for things like bearing failure and high oil consumption. However it does have a new replacement engine.
Good post, I've been wondering the same thing, I found this link on another forum:
q8oils-russia.com
It shows wear rates decreasing up 3.5 and then cut off at 3.5 It would be good to see chart after the right.
The big thing is oils started at X.X, but we know a lot of oils lose viscocity and probably are below 3.5 over time.
Low HTHS oils | News - GNV Oil Gruop
ООО «ДЖИ ЭН ВИ ОЙЛ ГРУПП», является официальным дистрибьютором корпорации «Кувейт Петролиум Интернейшнл Лубрикантс». И имеет эксклюзивное право на продажу продукции Q8 Oils на территории России, и в ряде стран СНГ.
It shows wear rates decreasing up 3.5 and then cut off at 3.5 It would be good to see chart after the right.
The big thing is oils started at X.X, but we know a lot of oils lose viscocity and probably are below 3.5 over time.
It can if the hydrodynamic friction from the higher dynamic viscosity is great enough to cause excessive bearing heat leading to fatigue of the soft metals. It takes a lot to make this happen though and unlikely with a daily commuter. It would be more likely in something like NASCAR with high rpm and tight bearing clearance. They see a ~75°F temp rise across the bearings with 0W-16 oil with oil temp at bearing exit around Daytona and Talladega at 350-360°F.
A higher-HTHS oil will only result in less wear when the oil is very hot.
When the oil is not very hot, thicker grades of oil will:
- Increase fuel consumption
- Reduce oil flow and delay oil pressure rise on cold starts
- Increase maximum cold oil pressure
- Increase likelihood of oil filter bypassing
- Increase load on battery and starter
- Increase engine load, which may increase wear of rings, liners, bearings during engine warm up
- Higher air and fuel flow may result in more dust contamination, filter loading, and injector wear
Thinner grades provide very small, but guaranteed benefits most of the time. The tradeoff is a higher risk of excessive wear in extreme conditions.
Here's a figure from a study showing bearing wear vs HTHS, with the engine at WOT with 150°C oil sump temperature. As viscosity is reduced, wear decreases, until it starts to increase exponentially. A 0W-20 would have little safety margin in this engine at 150°C (2.6 cP). With oil temperatures of 100°C, there would be plenty of safety margin since the viscosity would be >5 cP.
When the oil is not very hot, thicker grades of oil will:
- Increase fuel consumption
- Reduce oil flow and delay oil pressure rise on cold starts
- Increase maximum cold oil pressure
- Increase likelihood of oil filter bypassing
- Increase load on battery and starter
- Increase engine load, which may increase wear of rings, liners, bearings during engine warm up
- Higher air and fuel flow may result in more dust contamination, filter loading, and injector wear
Thinner grades provide very small, but guaranteed benefits most of the time. The tradeoff is a higher risk of excessive wear in extreme conditions.
Here's a figure from a study showing bearing wear vs HTHS, with the engine at WOT with 150°C oil sump temperature. As viscosity is reduced, wear decreases, until it starts to increase exponentially. A 0W-20 would have little safety margin in this engine at 150°C (2.6 cP). With oil temperatures of 100°C, there would be plenty of safety margin since the viscosity would be >5 cP.
The replacement engine will have the proper long life bearings.
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