Oil Viscosity vs Bearing Clearance

[thescreensavers]

If anyone wants to venture far down the rabbit hole on this topic, check out https://trackmustangsonline.com/threads/which-oil-to-use-for-track-days-for-2011-mustang-gt.13454/ These guys are running viscosities ranging from 5W-20 to 5W-50. They change oil after 1-2 days at the track or about every 2 hours or less.

My Camaro's V8 (LT1) was originally specc'ed for 5W30, but I can use 40wt oil on the track or street (per GM). The manual does also mention 50wt oils but asks that you drain it out after the track day. Track day oil temps with 40wt are in the 275s-280F

So that might be alluding to not run 50wt oils at cooler temps(grocery getting) as the oil which will be much thicker than a 30/40wt.

 

[kschachn]

My Camaro's V8 (LT1) was originally specc'ed for 5W30, but I can use 40wt oil on the track or street (per GM). The manual does also mention 50wt oils but asks that you drain it out after the track day. Track day oil temps with 40wt are in the 275s-280F

So that might be alluding to not run 50wt oils at cooler temps(grocery getting) as the oil which will be much thicker than a 30/40wt.

No the language about not running the 50-grade is about something else. The grade is not too thick for everyday driving in a technical sense.

 

[ZeeOSix]

So what's the consensus on heat and hydrodynamic friction when using a thicker oil in tight clearances? With reduced flow exiting the bearings and increased hydrodynamic friction from the increased viscosity, the oil's temperature rise through the bearing must be higher and bearing temps also higher.

I've noted spalling wear of the rod bearings from someone using a 20W-50 in an road racing engine with .0015-.0018" clearance. The mid-season oil change (after 5 events) showed >100 ppm of both Pb and Cu with a bunch of tin as well. The oil pan was removed, rod bearings pulled, and found spalling of the bearing surface. Oil sump temp would reach 280-290*F during the race with the bearing temps likely >350*F. Now, also note this was a '65 289ci V8 engine with stock replacement bearings. A modern engine with better alloys and aluminum block would likely take that heat better. The crank of that engine was still decent so it was just cleaned up and new bearings installed at the same clearance with a 5W-30 (Redline) used. The racing oil temp dropped down to ~260*F and they looked good as new after another 5 events.

I know Ford recommends Motorcraft 5W-50 for racing in the higher end models, but I don't know of anyone competitively racing those cars that actually uses a 5W-50 oil. The few I've had the liberty to check out were using 5W-30 or 0W-30. The drag racers are using 0W-20 or 0W-16.

No doubt that the oil temperature inside the bearing is going to heat up more with tighter bearing clearance, regardless of the oil viscosity. If the bearing clearance it too tight it could over heat even with lower oil viscosity. Another factor is how does the bearing clearance change as everything heats up? If the expansion coefficients of the materials used in the rod/crank/bearing are the same or very close then probably not a real factor, but who really knows.

Per the SubsTech link I gave in post #21 the oil shearing is higher with a smaller MOFT. A bearing with a low clearance will naturally run at a lower MOFT as compared to a bearing with a larger clearance (using the same oil) because the MOFT is a function of the clearance per the bearing Sommerfeld number. A thicker oil in the same bearing will run at a bit higher MOFT, which means the sear rate will be less, but from what I'm seeing it would still cause the oil temperature to increase a bit more even though it would be shearing the thicker oil at a lower shear rate.

There are two opposing factors going on at the same time. And of course, as the oil viscosity inside the bearing heats up more and more then the MOFT keeps going down and it kind of becomes a run-away situation. If it gets to the point of some level of metal-to-metal contact then things heat up even more. That's why keeping sump oil temperature in check in any race car with a good oil cooler is really key to the oil and engine surviving. A thinner oil may help reduce oil temperature, but it also decreases MOFT, so again there are two opposing factors going on, and which one will prevail to ensure the MOFT doesn't go to zero?

 

[ZeeOSix]

I've noted spalling wear of the rod bearings from someone using a 20W-50 in an road racing engine with .0015-.0018" clearance. The mid-season oil change (after 5 events) showed >100 ppm of both Pb and Cu with a bunch of tin as well.

Forgot to ask, what was the UOA KV100 of the oil after 5 events and how did it compare to the KV100 of that same oil when new? Some 50 weight oils shear down pretty quickly. And what was the HTHS and VI of that oil from the manufacturer?

 

[ZeeOSix]

For decades OEMs in the US have recommended low viscosity oils with overwhelmingly positive results.

Maybe not for extreme street use or track use. Even Toyota OMs in the USA make a comment that higher viscosity is better for high speed and high load use.

In Australia, Europe etc, on the other hand, a range of viscosity has been the approach. This has worked just as well.

If both are recommended, both will work just fine. The differences in longevity are so miniscule there isn't a comprehensive study that says otherwise...that I have ever found.

It's all about the use conditions. Don't use xW-16 or xW-20 for track use and don't use xW-50 for only going to the grocery store 2 miles away.

 

[Accent Abuser]

No the language about not running the 50-grade is about something else. The grade is not too thick for everyday driving in a technical sense.

It's bad for gas mileage and probably unnecessary.

 

[Accent Abuser]

So what's the consensus on heat and hydrodynamic friction when using a thicker oil in tight clearances? With reduced flow exiting the bearings and increased hydrodynamic friction from the increased viscosity, the oil's temperature rise through the bearing must be higher and bearing temps also higher.

I've noted spalling wear of the rod bearings from someone using a 20W-50 in an road racing engine with .0015-.0018" clearance. The mid-season oil change (after 5 events) showed >100 ppm of both Pb and Cu with a bunch of tin as well. The oil pan was removed, rod bearings pulled, and found spalling of the bearing surface. Oil sump temp would reach 280-290*F during the race with the bearing temps likely >350*F. Now, also note this was a '65 289ci V8 engine with stock replacement bearings. A modern engine with better alloys and aluminum block would likely take that heat better. The crank of that engine was still decent so it was just cleaned up and new bearings installed at the same clearance with a 5W-30 (Redline) used. The racing oil temp dropped down to ~260*F and they looked good as new after another 5 events.

I know Ford recommends Motorcraft 5W-50 for racing in the higher end models, but I don't know of anyone competitively racing those cars that actually uses a 5W-50 oil. The few I've had the liberty to check out were using 5W-30 or 0W-30. The drag racers are using 0W-20 or 0W-16.

If oil is getting hot enough to damage the bearings you probably need an oil cooler. Drag racers also rebuild their engines frequently, the only thing they have to worry about preventing is catastrophic block windowing.

 

[ZeeOSix]

If oil is getting hot enough to damage the bearings you probably need an oil cooler. Drag racers also rebuild their engines frequently, the only thing they have to worry about preventing is catastrophic block windowing.

To add, drag racers strive to get the oil temp and visosity to what they want when the tree goes green. The temperature isn't going to rise much enough to worry about over the next 1/4 mile or 1000 ft.

 

[RDY4WAR]

Forgot to ask, what was the UOA KV100 of the oil after 5 events and how did it compare to the KV100 of that same oil when new? Some 50 weight oils shear down pretty quickly. And what was the HTHS and VI of that oil from the manufacturer?

IIRC, it was VR1 20W-50. I can't remember the KV100, but I do remember not thinking anything remarkable of it so likely still within grade.

 

[Accent Abuser]

IIRC, it was VR1 20W-50. I can't remember the KV100, but I do remember not thinking anything remarkable of it so likely still within grade.

Well there's your problem. VR1 is a mineral base, which completely breaks down and fails to function as a lubricant at temperatures well below 300°F Had they been running Redline or Motul 300v 20w50 their bearings would have probably been just fine.

 

[wemay]

Maybe not for extreme street use or track use. Even Toyota OMs in the USA make a comment that higher viscosity is better for high speed and high load use.


It's all about the use conditions. Don't use xW-16 or xW-20 for track use and don't use xW-50 for only going to the grocery store 2 miles away.

Agreed 100%

 

[wemay]

Well there's your problem. VR1 is a mineral base, which completely breaks down and fails to function as a lubricant at temperatures well below 300°F Had they been running Redline or Motul 300v 20w50 their bearings would have probably been just fine.

Can you share a source for this information? (Everything except VR1 being mineral base)

 

[ChrisD46]

So , when say a Hyundai / Kia owners manual states : "5W20 , 5W30 or 10W30 weight oils are all acceptable in this engine - please select the oil used based on the expected ambient temps your next OCI is likely to see" . *All weights listed may be acceptable - which is ideal ?

 

[wemay]

So , when say a Hyundai / Kia owners manual states : "5W20 , 5W30 or 10W30 weight oils are all acceptable in this engine - please select the oil used based on the expected ambient temps your next OCI is likely to see" . *All weights listed may be acceptable - which is ideal ?

Here in S. Florida, I have used/use them all in the 2.0 or 2.4.

The 2.0T, OTOH, recommends 5/10w30, 5w40 and 15w40. I've used all of those in the Santa Fe Sport as well.

In all the H/K I've owned, it hasn't made a hill-of-beans difference.

 

[Jetronic]

Can you share a source for this information? (Everything except VR1 being mineral base)

If I crunch the numbers a bit that the pds provides, it appears VR-1 20W-50 might have a HTHS viscosity of around 4.5cP. Not terribly high, and it will drop even further, and fast, if the temp in the bearings exceeds 150C. Definitely below 4cP if the temperature rises to 160C and we don't know how hot that engine got. I can see it happening, spalled bearings.

VR-1 20W50 also comes as a synthetic (grp 3) with a much higher viscosity index....

 

[wemay]

If I crunch the numbers a bit that the pds provides, it appears VR-1 20W-50 might have a HTHS viscosity of around 4.5cP. Not terribly high, and it will drop even further, and fast, if the temp in the bearings exceeds 150C. Definitely below 4cP if the temperature rises to 160C and we don't know how hot that engine got. I can see it happening, spalled bearings.

VR-1 20W50 also comes as a synthetic (grp 3) with a much higher viscosity index....

Thanks, that's a logical progression of thought.

 

[2EHA]

VR-1 20W50 also comes as a synthetic (grp 3) with a much higher viscosity index....

160 VI is not the end of the world. GIII base content is less than 10%

 

[omegaspeedy]

Here in S. Florida, I have used/use them all in the 2.0 or 2.4.

The 2.0T, OTOH, recommends 5/10w30, 5w40 and 15w40. I've used all of those in the Santa Fe Sport as well.

In all the H/K I've owned, it hasn't made a hill-of-beans difference.

And to add, my New Zealand 2017 2.0 GDI Tucson allows a 50 grade per the user manual!

 

[Accent Abuser]

And to add, my New Zealand 2017 2.0 GDI Tucson allows a 50 grade per the user manual!View attachment 69373

The 1.6L GDI engine does too if you read the RHD manual.

 

[Cujet]

It's wonderful to concentrate on bearing clearance, a part that is unlikely to exhibit any wear at all in normal use. And completely ignore the chains that wear rapidly and the low tension rings that fail to seal after normal use.

As always, the oil change removes contaminates, particulates, evaporated fuel residues and other wee-beasties from circulating in the engine. The result of regular oil changes is generally long engine life.