Difference between different oil weights with similar HTHS?

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Back in the day, we used to have this thing called the Harrier jump-jet. It could take off vertically, hover...and get this...'bow' to the crowds at airshows! Of course we had other aircraft too... Tornadoes, Jaguars, venerable Vulcans, etc but the Harrier was 'what made us great'.

Which is odd because objectively, as a fighter aircraft, it really wasn't that great. Too expensive, too complicated, too slow, too thirsty, inadequate range, too little load carrying capacity plus a marked propensity for killing its pilots in accidents but hey, those bows. Oh we clapped & cheered!

As the decades have all too quickly ticked by, I have grown to regard the HTHS test as something not unlike the Harrier; an interesting & clever technical oddity which sounds important but actually isn't.

It's technically clever because it measures fresh oil viscosity at conditions of relatively high temperature (150°C), high speed & high rotating shear (like what you get in bearings). Under these conditions, the long chain polymeric molecules that make up the oils VII can 'align' & cause a partial but TEMPORARY drop in the oil's viscosity.

To which I say, so what? First off, unless you're hammering it at Daytona, your bulk oil temperature should never get anywhere near 150°C. Typically, bulk oil temperature tracks your coolant temperature so should top out somewhere around 100°C. I'd hazard a guess that over the last five years, my car's oil hasn't even hit 100°C because moderate speed/light load driving doesn't overstress the cooling system.

Let's also talk about the relative importance of HTHS as a test. I never kept track but as a calibrated stab in the dark, over the course of a typical crankcase oil development, I'd estimate I'd run 5,000 simple, drop tube kinematic viscosities for every ONE HTHS test. Say you were doing a Euro 5W30 program. Typically, at the start of the program, you'd check if you could make a commercial finished oil with 3.5 min HTHS without falling foul of the upper KV100 limit of 12.5 max. If yes, you might then ignore HTHS until you write up the Candidate Data Package at the end of the program. That's at the development stage. When it comes to the commercial blending of oils, I doubt if HTHS ever gets checked as part of anyone's regular QC regime.

And let's also acknowledge that the importance of HTHS is regularly & systematically undermined by the same people who insist that it's important & essential! Historically, the European OEMs were fixated on the importance of having oils which have an HTHS of 3.5 min. This figured prominently in the early ACEA specs & the CCMC specs which preceded ACEA. But then A1/B1 appeared allowing 2.9 min HTHS followed by A5/B5 which demanded you meet all the wear requirements of A3/B4 but yet allowed 2.9 HTHS. And while all this is going on, the Yanks have moved en masse to 5W20 with 2.6 min HTHS, demonstrating that it is realistically do-able!

My advice is try not to get too overly fixated on HTHS. I used to be 'that person' but I'm better now...
In BMW temperature of oil during cruising is between 110-120c. DME is running water pump and thermostat in a way that keeps oil temperature at higher level so it increases efficiency. The slower or, better word, economically you drive, the higher oil temperature is.
Go to a track, DME switches into high cooling mode keeping coolant temperature at lowest possible level. However, bcs. specificities of AMerican market, many US bound BMW's do not come with same cooling gadgets as EUropean models do (oil coolers, fluid/fluid heat exchangers) and than like I did, you end up on track running oil around 150c before DME cuts power. So yeah, HTHS does matter, but depends in which aplication.
 
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It appears that wear also correlated with engine RPMs. Most modern engines cruise at legal highway speeds at 2000rpm or less.

Another point, how does this accelerated wear equate to miles ? The question has been asked before. Does a 300k mile engine only go 290k on 20 grade oil?

We may never know the answer.
Good questions ... but it's been said in many studies and papers that the thinner you go the more propensity there is for wear. For me, I would rather give up 1% or less of increase in fuel economy than remove some protection head room of engine wear protection.

It's been known ever since the science of tribology was born (and one of the earliest know facts about lubrication) that oil viscosity is the primary factor that keeps moving parts separated (aka the 'film thickness') and that AW/AF additives are only the second defense to mitigate wear (aka 'film strength'). The science and physics of tribology won't ever change, but the formulation of oil can and does, and obviously as oil becomes thinner and thinner more AW/AF technology is trying to take more of the brunt when it come to wear mitigation.

 
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The most remarkable results though were the wear metal numbers which came off the ICP. Basically there were none! It took me a while to get my head around this because such a thin oil should have caused bad wear right? Then I realised that whilst the oil was relatively thin, if the oil spent most of those 9,000 miles below 100°C, then it would in absolute terms be relatively thick, thick enough to maintain a decent film strength & prevent wear.
Sound like a 'test' that showed the thicker oil resulted in less wear ... just sayin'. ;)
 
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Hard to explain away the notion that it's still the film thickness that keeps metal parts separated. I doubt that's going to change much any time soon.
Look at how long it's been known that the Earth is round ... yet many today still believe it's flat even in the light of science that it's not flat. 😆
 
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In BMW temperature of oil during cruising is between 110-120c. DME is running water pump and thermostat in a way that keeps oil temperature at higher level so it increases efficiency. The slower or, better word, economically you drive, the higher oil temperature is.
Go to a track, DME switches into high cooling mode keeping coolant temperature at lowest possible level. However, bcs. specificities of AMerican market, many US bound BMW's do not come with same cooling gadgets as EUropean models do (oil coolers, fluid/fluid heat exchangers) and than like I did, you end up on track running oil around 150c before DME cuts power. So yeah, HTHS does matter, but depends in which aplication.
I didn't know that. Point taken. That said, what you're describing sounds less like what I'd call a classic 'oil problem' (one which an oil formulator can influence) & more a problem with badly thought through German logic!

Also, if you really are seeing continuous oil temperatures of 150°C, then do you actually need a HTHS viscosity or might a easy-peasy, drop tube kinematic viscosity run at 150°C & a suitable spec range suffice? J-300 primarily defines oils with a min & max KV100 presumably because 100°C is roughly where oil typically tops out at. It would be a darn sight easier to specify a oil with a min & max KV150 for those folks who need this kind of thing. It's a frequent complaint on BITOG that the oil companies won't say what HTHS their oil has. Specify it & I suspect you would see KV150 on every single TDS with months.
 
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Also, if you really are seeing continuous oil temperatures of 150°C, then do you actually need a HTHS viscosity or might a easy-peasy, drop tube kinematic viscosity run at 150°C & a suitable spec range suffice? J-300 primarily defines oils with a min & max KV100 presumably because 100°C is roughly where oil typically tops out at. It would be a darn sight easier to specify a oil with a min & max KV150 for those folks who need this kind of thing. It's a frequent complaint on BITOG that the oil companies won't say what HTHS their oil has. Specify it & I suspect you would see KV150 on every single TDS with months.
The HTHS spec was invented because the oil runs hotter (150C+) in many critical parts of the engine ... like in the journal bearings and around the piston ring pack. I'm surprised you wouldn't know this if you've been in the oil formulation industry for years. Maybe oil formulators don't really get into the details of engine tribology (??). That's why ultimately HTHS is a better gauge for engine wear protection than just KV100. It's true in a general sense the an oil with a higher KV100 will also have a higher HTHS ... but not always, and it's not always equally proportional.
 
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It appears that wear also correlated with engine RPMs. Most modern engines cruise at legal highway speeds at 2000rpm or less.

Another point, how does this accelerated wear equate to miles ? The question has been asked before. Does a 300k mile engine only go 290k on 20 grade oil?

We may never know the answer.

Or we may... If that engine would have worn out rings by 300k on high hths oil and that would condemn it, going to an HTHS below 2.6 would half the life if revs exceed 2k. Since the average use will be a mix of rpms, the question is what ratio... if half the time the revs exceed 2k, we're talking about roughly 225k engine life. Question is the oil temp, is 130C realistic between the piston rings and cylinder? I believe that's on the low side, with the coolant around 100C and the ringlands being significantly hotter.

Now if that 300k engine gets tossed out because of timing chains going out, maybe it all doesn't make any difference.
 

skrypj

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I didn't know that. Point taken. That said, what you're describing sounds less like what I'd call a classic 'oil problem' (one which an oil formulator can influence) & more a problem with badly thought through German logic!

Also, if you really are seeing continuous oil temperatures of 150°C, then do you actually need a HTHS viscosity or might a easy-peasy, drop tube kinematic viscosity run at 150°C & a suitable spec range suffice? J-300 primarily defines oils with a min & max KV100 presumably because 100°C is roughly where oil typically tops out at. It would be a darn sight easier to specify a oil with a min & max KV150 for those folks who need this kind of thing. It's a frequent complaint on BITOG that the oil companies won't say what HTHS their oil has. Specify it & I suspect you would see KV150 on every single TDS with months.

I think this is exactly why you see performance motors from companies like Ford specifying 50 weight oil, while the same motor in other applications specs 30 weight.

Example, if you get the Mustang with the High Peformace Ecoboost it comes with 50 weight, even though it shares many of the same internals with the regular 2.3. Same with the 5.0 V8 with the track pack.

I started this thread in a general way, but in the back of my mind I was thinking about my 3.5L boosted motor pulling 13000+ pounds of truck and trailer up a mountain in 100°F heat. That is sustained high output for 5-10 minutes straight possibly with very high ambient temperature resulting in poor cooling system performance.
 
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Had the tests been carried out at 100°C (which is the more typical maximum temperature for engine oil in normal service) things would have looked far more benign. Had the tests reflected true driving reality where the oil cycles between cold & warmed up (10°C to 100°C) it would be even more benign still.
Hi, @Sonofsonof ,
Happy to see you again :)
In fact, a very similar test was performed. Here are the results with the oil temperature at 90 C
HTHS90_1.jpg

You can see the rest of the tests carried out by Toyota R&D in 1997 here:
 

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12,181
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I didn't know that. Point taken. That said, what you're describing sounds less like what I'd call a classic 'oil problem' (one which an oil formulator can influence) & more a problem with badly thought through German logic!

Also, if you really are seeing continuous oil temperatures of 150°C, then do you actually need a HTHS viscosity or might a easy-peasy, drop tube kinematic viscosity run at 150°C & a suitable spec range suffice? J-300 primarily defines oils with a min & max KV100 presumably because 100°C is roughly where oil typically tops out at. It would be a darn sight easier to specify a oil with a min & max KV150 for those folks who need this kind of thing. It's a frequent complaint on BITOG that the oil companies won't say what HTHS their oil has. Specify it & I suspect you would see KV150 on every single TDS with months.
BMW logic was that bcs. in US cars do not see speed etc. like in Europe, and bcs. climate, it really does not need robust cooling system, as trend was toward efficiency. Keep engine as hot as possible and try to retain heat in engine compartment as long as possible.
It did backfire as turbo models had huge issues during testing by Motor Trend, C&D etc. where they would overheat in no time (especially high altitude tracks, which plagued my car too). I mean they delivered vehicle with outsized oil sump (it is inline 6 afterall), has basically brakes ready for track, etc. and yet, in chase for mpg, they botched that.
Current BMW's come loaded with coolers and various heat exchangers (it does not look fun at all to fix, whoever ends up doing that). Even regular inline six models have fluid/fluid exchanger and two oil coolers. But, still we are talking temperatures in 130's on track easily.
As for my car, I retrofitted oil cooler from 335 turbo model to my naturally aspirated. Thermostat is opening at 110c, and it works so well that few days ago at -24 degrees I had no problem keeping oil around 100-105c while cruising.
So, IMO, HTHS gives at least some indication of how oil will perform in those areas where temperature is much higher than oil sump, where oil temperature sensor is. I guess providing KV150 would be beneficial. Heck, give me all possible info, so I can make best decision that I am able to. That is why I appreciate Mobil1 for example as they provide much more info than Castrol, Pennzoil. Valvoline is also decently transparent.
 
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I like a3/b4 type oil ... However, what are the significance of piston ring wear increases in these charts? how does that translate into real-life?

also based on these charts (130C and 90C graphs on page 1 & 2) looks like there is hardly any diff in the wear for hths of 2.6 or higher. Aren't even the thin xW20s at or over the 2.6?
 
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I think this is exactly why you see performance motors from companies like Ford specifying 50 weight oil, while the same motor in other applications specs 30 weight.

Example, if you get the Mustang with the High Peformace Ecoboost it comes with 50 weight, even though it shares many of the same internals with the regular 2.3. Same with the 5.0 V8 with the track pack.

I started this thread in a general way, but in the back of my mind I was thinking about my 3.5L boosted motor pulling 13000+ pounds of truck and trailer up a mountain in 100°F heat. That is sustained high output for 5-10 minutes straight possibly with very high ambient temperature resulting in poor cooling system performance.
Don’t worry about ambient temperature. Worry about altitude. That is real problem when it comes to cooling.
 
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Is that due to the thin air being less efficient at removing heat from the radiator and other heat exchangers?
Yep. Less efficient heat exchange.
one example:
In 2013 went to pick up wife’s car in Charlottesville, VA, and drove it back to San Diego. Went through AZ, middle of heat wave. Drove on I8 120mph, 128f ambient temperature. Car did not blink. We move that year to Colorado Springs, drove it to Pikes Peak, with HVAC full on to help cooling, ambient temperature 45, coolant temperature went from middle to 3/4. Had to keep car running at the top to cool it off.
 

skrypj

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Yep. Less efficient heat exchange.
one example:
In 2013 went to pick up wife’s car in Charlottesville, VA, and drove it back to San Diego. Went through AZ, middle of heat wave. Drove on I8 120mph, 128f ambient temperature. Car did not blink. We move that year to Colorado Springs, drove it to Pikes Peak, with HVAC full on to help cooling, ambient temperature 45, coolant temperature went from middle to 3/4. Had to keep car running at the top to cool it off.
This is the exact issue with the F150 Ecoboosts. They seem to be fine at sea level, but when you get up in altitude they overheat while towing.

the issue is that they still make the factory power ratings at 7000+’ because of the turbos, but have 20% less air mass flowing through the radiator
 
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This is the exact issue with the F150 Ecoboosts. They seem to be fine at sea level, but when you get up in altitude they overheat while towing.

the issue is that they still make the factory power ratings at 7000+’ because of the turbos, but have 20% less air mass flowing through the radiator
Does it have oil cooler? Some kind heat exchanger? Running heat on max full blast helps a lot.
 
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The HTHS spec was invented because the oil runs hotter (150C+) in many critical parts of the engine ... like in the journal bearings and around the piston ring pack. I'm surprised you wouldn't know this if you've been in the oil formulation industry for years. Maybe oil formulators don't really get into the details of engine tribology (??). That's why ultimately HTHS is a better gauge for engine wear protection than just KV100. It's true in a general sense the an oil with a higher KV100 will also have a higher HTHS ... but not always, and it's not always equally proportional.

Hi, @Sonofsonof ,
Happy to see you again :)
In fact, a very similar test was performed. Here are the results with the oil temperature at 90 C
View attachment 45690
You can see the rest of the tests carried out by Toyota R&D in 1997 here:
Thanks for this. It sort of confirms what I'd expect to see (ie naff all!).
To me, this reflects the more 'normal' scenario; when people aren't towing or racing or at altitude but more mundanely doing the morning commute at a steady 65 mph.
When I see the two charts side by side, it reminds me of how the industry often approaches this kind of thing. If you can't find differentiation at normal conditions, whack up the test severity until you can. I have no doubt that had Toyota upped the bulk oil temperature to 150°C+, they could have conclusively 'proved' that the xxW-30s that folks have used for the last 30 years were 'inadequate'.
 
Messages
80
I like a3/b4 type oil ... However, what are the significance of piston ring wear increases in these charts? how does that translate into real-life?

also based on these charts (130C and 90C graphs on page 1 & 2) looks like there is hardly any diff in the wear for hths of 2.6 or higher. Aren't even the thin xW20s at or over the 2.6?

Regarding your last point, the specs might say 2.6 min HTHS but it's actually tricky to make a commercial oil 'tight' against the minimum spec. The quality of individual batches of base oil, DI & VII can bounce around; not by much but they do. If you aim for 2.6 dead, you might occasionally blend up a batch of oil with a 2.54 cP HTHS which is nominally off-grade (remember blend plants work to FIXED formulations. They are generally never tweaked or trimmed to suit). For this reason, most commercial blenders blend conservatively so HTHS is often higher than the spec permits.

If also worth pointing out that sometimes 'the system' works against you. Euro A3/B3/B4 xxW-30 oils not only have to meet 3.5 min HTHS but also 12.5 cst max KV100 & sometimes the two specs can be mutually exclusive. Unlike in the US, 10W30 engine oils are almost unheard of in Europe because of the impossibility of meeting both specs at the same time. To get to 3.5 min HTHS you sort of need the KV100 to be 12.7 cst whereas a commercially acceptable, blendable 12.3 cst KV100 might only yield an HTHS of 3.35 cP.

I suspect, if you went out & checked, there are probably quite a few xxW-30 A3/B3/B4 oils out there that are like this & technically off-grade for HTHS. However as HTHS is not a widely available test, this anomaly is hardly ever picked up on. It might also part-explain why 5W40s are pushed because these circumvent this issue.
 
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