Optimal kinematic viscosity for mimimal wear?

[Gary Allan]

Originally Posted By: Steve S
Originally Posted By: Gary Allan
Quote:
I don't think over the road trucks are operated at near maximum loads. The good drivers even when going up hills gear for minimum load on the engine otherwise the turbos will get too hot.


Would you buy a tri-axle dump only to put 5yrds of dirt in it and tool around the countryside? Would you buy a Class 8 rig and only load it to 20k. Would you waste the money. How about a bulldozer or a loader ..and only use them to 10% capacity?

No, you wouldn't. We drive cars and ..by gosh ..even pickup trucks way below their sensible limits.

Please ..(sigh) ..oh, never mind.
Gary you are not really getting this post Since I have enough experience ,since I owned a semi for several years running coast to coast in these lower 48 states .I can with authority there is NO over the road truck and I would bet any aircraft that ever operates constantly at or near maximnm engine loads. Reread the original post. If interested My neighbor is an ex Marine fighter jock and now drives a commercial jet for a major airline about planes operation as it pertains to operating an maximum engine output.


My fine experienced friend... All of those conveniences have routine service capabilities that are fully assured to be tested when you buy the darn things. Tell me that, in your coast to coast distractions, you never encountered a 6-8% grade fully loaded? Tell me that that air craft never used FULL POWER at any time and that FULL POWER was what the given engine may have to encounter frequently and/or for sustained periods of time

It's the same for an industrial piece of equipment. The service is dictated by the things existence to begin with. The lubricant used is to allow it to work at MAX utility without undue refit time or failure in service UNDER THOSE CONDITIONS.

In your OTR sector, the lubricant happens to work out to 15w-40 in all things balanced to sensible economy.

Why not 50 weight? Why not 60 weight? 70? I mean ..if there's not terminal end to the theory/science, then why aren't they using those weights. They exist ..and they'll keep metal parts WAY further apart under all conditions.

The sword has to cut both ways.

This is too fundamental a concept. It's the same with your Euro-Alloy. They are designed for high speed sustained usage and are of higher power density.

 

[mechtech2]

That old saying that 'Most wear occurs at start up." has some real truth to it.
And we must consider that thicker oils run hotter. All of what I have seen with oil temp gauges on vehicles, and pretty much all of what I have heard indicates this.

 

[CATERHAM]

Originally Posted By: zoomzoom
Originally Posted By: CATERHAM
So getting back to the original question, the optimal kinematic vis for minimal wear. Perhaps I should have said the optimal "minimum" viscosity because that's what we're really talking about hear. No offense to those in the thick camp but it seems kind of silly to see how thick an oil one can safely run with all the other negative attributes of running an oil heaver than necessary.

Pablo felt a 30 wt range of 9.3 cSt to 12.5 cSt as being too narrow depending on bearing size (width I presume) etc.
Would 8.0 cSt be a non issue? How about 6.5 cSt which happens to coincide with a couple of the lighter 20 wt oils available (eg RP XRP 5W-20 and 0W-10 of which their are a couple of excellent UOA's hear).
I'm thinking 6.5 cSt may be as low as you'd want to go before wear would start to ramp up? It may be OK to run oils into the 4 cSt range but wouldn't you be getting into frequent boundary lubrication with oil that thin by that time? Keep in mind we're talking maximum load situations; back out of the throttle and I would think vis of 2 cSt is no problem.

Maybe Gary Allen would know; has the SAE ever done tests of this sort?


I think you are asking wrong question, HTHS viscosity is the one that has more impact on the engine wear.

You want to be above 2.6 HTHS in a regular use street driven car, but 3 would be better..high performance engines like > 3.5


Zoom, maybe you're right and the HTHS vis is what one should pay more attention to as the safe lower vis limit, in which case the safety margin when a mfr recommends an oil is huge IMO.

So if you know what your maximum oil temperatures are (and unfortunately most of us don't because the mfr's usually do not provide oil temp or pressure gauges) then you can quickly establish just how big that safety margin you want to run in how you operate your car.
If as I suspect, the oil temp's don't get much above 100C or even 110C and a 20 wt is spec'd for your car (HT/HS of 2.6) then the lightest fully formulated oil you can get your hands on (0W-10 ?) is more than adequate.
And in a high performance car where a higher HT/HS vis of say 4.5 is spec'd and your oil temp's don't get above 120C a 20 wt oil is all you need.
With so much of an engines running time spent just coming up to temperature in most typical situations it can only be benificial running the lightest oil possible.

 

[Bryanccfshr]

Most engines don't get the oil temp to 100°c It is more like 180-190°f and they quicly drop off once the load is taken off the engine.

 

[zoomzoom]

Originally Posted By: CATERHAM
Originally Posted By: zoomzoom
Originally Posted By: CATERHAM
So getting back to the original question, the optimal kinematic vis for minimal wear. Perhaps I should have said the optimal "minimum" viscosity because that's what we're really talking about hear. No offense to those in the thick camp but it seems kind of silly to see how thick an oil one can safely run with all the other negative attributes of running an oil heaver than necessary.

Pablo felt a 30 wt range of 9.3 cSt to 12.5 cSt as being too narrow depending on bearing size (width I presume) etc.
Would 8.0 cSt be a non issue? How about 6.5 cSt which happens to coincide with a couple of the lighter 20 wt oils available (eg RP XRP 5W-20 and 0W-10 of which their are a couple of excellent UOA's hear).
I'm thinking 6.5 cSt may be as low as you'd want to go before wear would start to ramp up? It may be OK to run oils into the 4 cSt range but wouldn't you be getting into frequent boundary lubrication with oil that thin by that time? Keep in mind we're talking maximum load situations; back out of the throttle and I would think vis of 2 cSt is no problem.

Maybe Gary Allen would know; has the SAE ever done tests of this sort?


I think you are asking wrong question, HTHS viscosity is the one that has more impact on the engine wear.

You want to be above 2.6 HTHS in a regular use street driven car, but 3 would be better..high performance engines like > 3.5


Zoom, maybe you're right and the HTHS vis is what one should pay more attention to as the safe lower vis limit, in which case the safety margin when a mfr recommends an oil is huge IMO.

So if you know what your maximum oil temperatures are (and unfortunately most of us don't because the mfr's usually do not provide oil temp or pressure gauges) then you can quickly establish just how big that safety margin you want to run in how you operate your car.
If as I suspect, the oil temp's don't get much above 100C or even 110C and a 20 wt is spec'd for your car (HT/HS of 2.6) then the lightest fully formulated oil you can get your hands on (0W-10 ?) is more than adequate.
And in a high performance car where a higher HT/HS vis of say 4.5 is spec'd and your oil temp's don't get above 120C a 20 wt oil is all you need.
With so much of an engines running time spent just coming up to temperature in most typical situations it can only be benificial running the lightest oil possible.


I will give you my example. I drive twin turbo Audi S4 and I have oil temp gauge in it. Car is modified and I take it to the racetrack 3-4 times a year.

In my daily commute (7 miles to work, 30% city 70% hwy) I usually get oil to about 175-180F by the time I pull in to parking lot at my work now in summer time.

In winter oil barely passes 150-155F mark for the same commute.

Prolonged hwy drive results in oil temps 225-230F

At the racetrack oil gets to 275-280F after couple laps and stays there till the end on the session(25-30min)

Audi specs A3 rated oil and 0W-30(factory fill) to 5W-40 viscosity.

Looking at my conditions one would say I could easily run 20wt for my round town driving, but then again car is modified and puts out 360HP (stock trim was 250HP), but when I put the pedal to the floor or flog it on the racetrack 20wt is just not going to cut it, but I did found that 30wt(GC) is up to the task of protecting engine and keeping the wear down as confirmed by my UOA while not robbing me of the power.

Currently I am running redline 5w-30 in it and will be curios to see how oil with lower kinematic viscosity but higher HTHS then GC does in the car...

Here is graph showing how long it takes for oil and coolant to reach operational temperature in my car. This data was collected when my daily commute was a bit longer, 15 miles to my former employer:

Looking at this data it is obvious that even if I had 20wt oil in the car in reality most of the time I would be driving on much higher viscosity oil!

 

[saaber1]

zoomzoom, very nice graph! Good job! So it takes roughly 6 min for coolant to get to temp and 12 min for oil to get to temp on that engine. What season was this data collected in?

 

[saaber1]

Just an idea, but you could use Widman's viscosity calculator to show the various viscosities at different times during warm up either graphically or as a few annotations to key points on the oil temp line, that would be pretty cool. I think GC kv100 is 12.2 but I don't know GC's 40C viscosity for widman's calculator. edit: Is it 68.5?

 

[zoomzoom]

Originally Posted By: saaber1
zoomzoom, very nice graph! Good job! So it takes roughly 6 min for coolant to get to temp and 12 min for oil to get to temp on that engine. What season was this data collected in?


I think it was late spring/early summer...and that was from work to home where I get on highway immediately.

The one below was from home to work and it was winter time:

ADMIN NOTE: I captured this image and shrank it down to 600 pxl wide. For all members -- please remember to make the images you post no more than ~600 pxl wide, or it makes the thread nearly unreadable, especially for those with laptops or smaller screens. Thanks.

 

[saaber1]

Wow! Amazingly small difference in warm up times (roughly 2 minutes longer for both coolant and oil in Wash DC winter). Very good info! Smaller difference than I would have presumed.

Also I noticed on the first graph looking at speed line that the hwy portion starts about 6 min. in. while on the winter graph hwy portion starts about 9 min. in. I wonder if that isn't a bigger factor than the seasonal temp change?

 

[zoomzoom]

at these speeds I doubt it since there is not much of the slope change before and after getting on highway

admin put the wrong picture back..here is the winter drive:

 

[Geonerd]

Originally Posted By: Rickey

Ok so some one speak up.

ME's please.


Actually, Mr. Spock, someone with experience in electronic circuits would likely possess the more accurate instincts. The flow of oil through an engine seems quite similar to the movement of electrons through a moderately complex resistor network.

 

[CATERHAM]

Zoom, my experience is similar to yours.

The car I routinely track is my Caterham. It has a 185 HP 2 liter four with a heavily finned aluminium sump.
While I've always suspected the oil temps never really got that high based on water temp and oil pressure it wasn't until I installed an oil temp gauge this year that I realized how cool it actually runs.
At Mosport this year, running GC 0W-30 the maximum oil temps leveled off at 95C after a few lapse and stay there with the oil pressure at 82 psi @ 6,500 rpm. BTW it was a 85 F sunny day.
But on the street I'm hard pressed to get the oil temps above 70C
unless I'm cruising at a fairly high speed of 90 mph and the temps will rise to 80C.
I recently changed out the GC and filled with Red Line 0W-20.
Another track day at Mosport, same maximum oil temp of 95C but the oil pressure dropped to 72 psi which is not surprising going from 12.1 cSt @ 100C to a 8.2 @ 100C oil. Actually, since I'm not hitting 100C I figure the RL oil vis is around 9.1 cSt.
So now I'm considering substituting a qt of RL 5 wt ( 0W-5 ) race oil with the 0W-20 to give a 100C vis of about 7.4 cSt.
( for those that don't know it's perfectly acceptable to blend RL oils including race and street oils). The limiting factor on how low I go on vis is my oil pressure which I've targeted at 65 psi.

 

[BuickGN]

I'm all for the highest HTHS for the viscosity. If I could find a 10w with a 3.5 HTHS or better and assuming it provides adequate oil pressure, I would run it.

Elk, what I think you're not getting is an oil doesn't just protect or not protect. It's not all or nothing. Some oils do protect better than others. The info is out there and this is fact, not opinion. Do you just ignore the testing done my GM that showed a huge reduction in bearing wear by increasing HTHS 1.5 points?

 

[CATERHAM]

Zoom, I've run both Red line 5W-30 and 10W-30.
You know how RL claims their oils behave like the next highest grade mineral or other syn's when it come to in bearing vis',
and that has largely been my experience.
I think you'll find the RL 5W-30 will act on par with GC or even like a somewhat heavier oil.

The Widman viscosity chart doesn't appear to work well on vis from 100C to 150C. Anybody got some suggestions on that?

I believe I've read the relationship between the kinematic vis at 150C and HT/HS at 150C is not the same? Anybody know anything about that?

 

[MolaKule]

Quote:
"Rust protection is achieved by metalworking fluid containing mineral oil. Synthetic lubricants do not provide proper corrosion protection." from http://www.substech.com/dokuwiki/doku.php?id=cutting_fluids_coolants

"Rust protection oils are commonly based on mineral oils (either paraffinic or naphtenic)." from http://www.substech.com/dokuwiki/doku.php?id=rust_protection_oils


You are discussing metal working fluids that may use water as part of the emulsion.

Different animal dude. PCMO's have a totally different formulation.

Quote:
Rust protection oils are commonly based on mineral oils (either paraffinic or naphtenic).


Old data. Any base oil can serve as a rust protetion oil.

 

[CATERHAM]

MolaKule, good to hear from you but are you on the wrong thread?

 

[FZ1]

Very interesting. Thanks,man. That's why I always try to run my longest errand 1st.

 

[Junior]

Originally Posted By: ekpolk
Originally Posted By: BuickGN
Where's the article that stated that increasing the HTHS up to something crazy like 11 or 16 reduced wear with each increase...

I'm sure that such a substance would run just beautifully in an Accord or Camry...

Originally Posted By: BuickGN
And come on guys with this whole thing about bearings and cylinders hanging on till the oil pressure arrives. Oil pressure isn't more than half a second behind the first revolution of the crank.

Is it? Always? Well, if you assume that everything is optimum, and you have an engine that idles at ~800 rpm, and it's of course starting from zero rpms, and using your 1/2 sec assumption, then by my rough calculations, the engine will experience a couple dozen or so revolutions without oil pressure. Not disastrous, but certainly enough to raise the specter of wear happening on start. Particularly when considered on a cumulative basis.

I would neither over-minimizing, nor overdramatize, this phenomenon. Again, why would the Toyota engineers felt it necessary to have the hybrids pre-oil themselves on start? Why are pre-oilers for sale?


One thing I would like to add is that while we assume oil is incompressible it is slightly compressible. For the low pressures we are talking about in an automotive application it is basically a non-factor. Get to 6,000+ psi it can be a factor.

Secondly, oil pressure is not required for hydrodynamic lubrication. It is only the means to supply oil to the journal bearing. There is some residual oil in the bearings at start-up. I don't disagree that more wear can occur at start-up/warm up phase, I just don't know the percentage. I agree that pressure does help the splash or spray type lubrication.

It isn't accurate to say a higher viscosity fluid will separate a bearing better without specifying the bearing load, speed, width, diameter and clearance. The calculations for determining the required viscosity for a journal are actually straight forward in a fluid dynamics book. In general for a given journal bearing, the lower the load or higher the speed the lower viscosity required. The viscosity selected must work across the expected loading, speed and temperature ranges. One can also calculate the temperature rise of the fluid moving through the bearing.

The reason I would assume OTR trucks use 15W40 is because they have higher loadings and oil temperatures and spend a larger part of their lives as a high power output. IIRC, the assumed duty cycles for automotive/OTR truck/offroad equipment are roughly 30%/60%/90% of the time at full power output.

 

[Gary Allan]

Quote:
The reason I would assume OTR trucks use 15W40 is because they have higher loadings and oil temperatures and spend a larger part of their lives as a high power output. IIRC, the assumed duty cycles for automotive/OTR truck/offroad equipment are roughly 30%/60%/90% of the time at full power output.


Thank you.

 

[Steve S]

Originally Posted By: Gary Allan
Originally Posted By: Steve S
Originally Posted By: Gary Allan
Quote:
I don't think over the road trucks are operated at near maximum loads. The good drivers even when going up hills gear for minimum load on the engine otherwise the turbos will get too hot.


Would you buy a tri-axle dump only to put 5yrds of dirt in it and tool around the countryside? Would you buy a Class 8 rig and only load it to 20k. Would you waste the money. How about a bulldozer or a loader ..and only use them to 10% capacity?

No, you wouldn't. We drive cars and ..by gosh ..even pickup trucks way below their sensible limits.

Please ..(sigh) ..oh, never mind.
Gary you are not really getting this post Since I have enough experience ,since I owned a semi for several years running coast to coast in these lower 48 states .I can with authority there is NO over the road truck and I would bet any aircraft that ever operates constantly at or near maximnm engine loads. Reread the original post. If interested My neighbor is an ex Marine fighter jock and now drives a commercial jet for a major airline I can ask about planes operation as it pertains to operating an maximum engine output.


My fine experienced friend... All of those conveniences have routine service capabilities that are fully assured to be tested when you buy the darn things. Tell me that, in your coast to coast distractions, you never encountered a 6-8% grade fully loaded? Tell me that that air craft never used FULL POWER at any time and that FULL POWER was what the given engine may have to encounter frequently and/or for sustained periods of time

It's the same for an industrial piece of equipment. The service is dictated by the things existence to begin with. The lubricant used is to allow it to work at MAX utility without undue refit time or failure in service UNDER THOSE CONDITIONS.

In your OTR sector, the lubricant happens to work out to 15w-40 in all things balanced to sensible economy.

Why not 50 weight? Why not 60 weight? 70? I mean ..if there's not terminal end to the theory/science, then why aren't they using those weights. They exist ..and they'll keep metal parts WAY further apart under all conditions.

The sword has to cut both ways.

This is too fundamental a concept. It's the same with your Euro-Alloy. They are designed for high speed sustained usage and are of higher power density.
Going up a steep grade isn't put your foot to the floor and pick the gear that will get you the fastest speed over the hill . I never mentioned that engines never are run at 100% did I ? Usually engines operate at a less than full throttle engine load most of the time. Remember if a 40 wt keeps the metal seperated as needed a 60 wt will not necessarily keep them apart more better.