Striking the Right Balance

[buster]

http://www.infineum.com/InfineumInsight/Insight59/main.swf?page=10

Pg 10 of the Infineum Insight Mag talking about FE challeges with low vis oils. VM'er plays a very important role.

 

[A_Harman]

I really like the part where they describe what happened when they tested a heavy duty diesel with an oil having HTHS of 2.6:

"While the exact sequence of events leading to the engine failure could not be established, it is believed that excessive wear in one of the crank assembly components resulted in sezure of the crankshaft, causing it to break and exit from one side of the engine body. However when the same engine test was run using SAE 15w40 using the same additive technology an excellent passing performance was observed."

Here's a sobering warning about the relentless pursuit of thin oil. What else should they expect, considering they were running 2.6 HTHS oil in and engine designed for 3.7 HTHS? The elegance of hydrodynamic bearings is there is no metal to metal contact when the system is working as designed. By putting in thinner oil than the engine was designed for, they pushed the system out of its designed regime. So now the engine bearings need to be redesigned to work with the thinner oil. Talk about the tail wagging the dog...

 

[buster]

+1^

 

[demarpaint]

Originally Posted By: buster
+1^


+2

 

[cp3]

But if that engine is being operated mildly and oil temperature is not as high as it's designed regime, is it not possible that the thinner oil would now be at a similar viscosity allowing the bearing to function as designed? Keep in mind most of our discussions revolve around a difference of 3.0/3.1 to 2.7/2.8 not 3.7/2.6.

 

[CATERHAM]

Yes I had to laugh at infineum's reporting matter of factly their experiment of a 2.6cP 20wt oil with an API CJ-4 add' pack' in a conventional heavy-duty diesel resulted in "catastrophic engine damage" vs a 4.0cP 15w40, as if that would be a surprise.

Diesel engines particularly in long haul trucking have their own set of issues in the pursuit of increased fuel economy through lower viscosity engine oils. There is a move to incrementally lighter 10w30 and 5w30 HDEOs with the API's new up coming PC-11 specification.

Of course Europe has a huge variety of light duty diesels running reasonably light C2 0W/5w30 (HTHSV 2.9cP-3.0cP) mid-SAP motor oil without issue.

 

[A_Harman]

When I said the tail was wagging the dog, I was referring to the irony of redesigning the whole engine so that thin oil could be run. The same applies to the cooling system of a vehicle. Yes, a 20-weight oil can provide the same viscosity in a bearing as a 40-weight oil as long as it can be reliably controlled to the lower temperature at all operating conditions. This would require that the vehicle be redesigned for a larger radiator. The larger radiator on the vehicle adds weight and increases aerodynamic drag, which may overcome the 2% fuel consumption reduction that the thinner oil provides inside the engine.

Plotting viscosities of Pennzoil Ultra 5w20 and VPB 15w40 versus temperature shows that if VPB is being run at 120C, its viscosity is 9.7 cSt. In order to assure that the Pennzoil Ultra 5w20 maintains the same viscosity, its temperature must be controlled to 93C. This 27C (that's 48.6 F) drop in operating temperature can only be accomplished by a much larger radiator.

 

[cp3]

Gotchya! Same page.

 

[buster]

Quote:
When I said the tail was wagging the dog, I was referring to the irony of redesigning the whole engine so that thin oil could be run.


I knew exactly what you meant and I totally agree. There has to be better ways to improve FE.

 

[kschachn]

Oh, I like it too. What a huge load of baloney that is.

A sample size of one, with words like "could not be established" and "believed". Really? You could not establish that hydrodynamic boundary layer failure caused the damage? Really? What kind of testing facility are you then?

Worthless except as a sensational statement.

Originally Posted By: A_Harman
I really like the part where they describe what happened when they tested a heavy duty diesel with an oil having HTHS of 2.6:

"While the exact sequence of events leading to the engine failure could not be established, it is believed that excessive wear in one of the crank assembly components resulted in sezure of the crankshaft, causing it to break and exit from one side of the engine body. However when the same engine test was run using SAE 15w40 using the same additive technology an excellent passing performance was observed."

Here's a sobering warning about the relentless pursuit of thin oil. What else should they expect, considering they were running 2.6 HTHS oil in and engine designed for 3.7 HTHS? The elegance of hydrodynamic bearings is there is no metal to metal contact when the system is working as designed. By putting in thinner oil than the engine was designed for, they pushed the system out of its designed regime. So now the engine bearings need to be redesigned to work with the thinner oil. Talk about the tail wagging the dog...

 

[CATERHAM]

Originally Posted By: A_Harman

Plotting viscosities of Pennzoil Ultra 5w20 and VPB 15w40 versus temperature shows that if VPB is being run at 120C, its viscosity is 9.7 cSt. In order to assure that the Pennzoil Ultra 5w20 maintains the same viscosity, its temperature must be controlled to 93C. This 27C (that's 48.6 F) drop in operating temperature can only be accomplished by a much larger radiator.

But no street engine I'm aware of operates with normal oil temp's of 120C. You may see 120C oil temp's under some extreme operating conditions such as a period of sustained full power but in returning to a more normal power output level the oil temp's will also return to normal.

Besides there are a number of ways to control maximum oils temp's from an engineering perspective. Anyone who has experimented with different thermostats knows just how much excess radiator capacity most vehicles have even on the hottest days.
And of course with the advent of modern electronic safety management systems, should oil temp's rise above a certain level it's a simple matter to gradually limit maximum power to reduce the rise to the predetermined maximum oil temp's allowed and therefore how thin the specified oil will get.

 

[demarpaint]

Originally Posted By: buster
Quote:
When I said the tail was wagging the dog, I was referring to the irony of redesigning the whole engine so that thin oil could be run.


I knew exactly what you meant and I totally agree. There has to be better ways to improve FE.


+1

 

[A_Harman]

Originally Posted By: cp3
Gotchya! Same page.


Maybe a bit. Hopefully I wasn't sounding like I was up on a soapbox. Your question did get me doing some calculations to see what the oil temperatures would give equivalent viscosities between 20 and 40 weights. I found the exercise useful.

 

[A_Harman]

Originally Posted By: CATERHAM
Originally Posted By: A_Harman

Plotting viscosities of Pennzoil Ultra 5w20 and VPB 15w40 versus temperature shows that if VPB is being run at 120C, its viscosity is 9.7 cSt. In order to assure that the Pennzoil Ultra 5w20 maintains the same viscosity, its temperature must be controlled to 93C. This 27C (that's 48.6 F) drop in operating temperature can only be accomplished by a much larger radiator.

But no street engine I'm aware of operates with normal oil temp's of 120C. You may see 120C oil temp's under some extreme operating conditions such as a period of sustained full power but in returning to a more normal power output level the oil temp's will also return to normal.

Besides there are a number of ways to control maximum oils temp's from an engineering perspective. Anyone who has experimented with different thermostats knows just how much excess radiator capacity most vehicles have even on the hottest days.
And of course with the advent of modern electronic safety management systems, should oil temp's rise above a certain level it's a simple matter to gradually limit maximum power to reduce the rise to the predetermined maximum oil temp's allowed and therefore how thin the specified oil will get.


You're thinking of passenger car engines that operate at light and variable loads. In this context I'm thinking of heavy duty diesels, that operate at continuous heavy loads. 120 C is on the high side of normal for those engines, but not rare. I used to run a standard test at Cummins known as the Hot Box test. 200 hours at rated power with coolant temperature at 230F. This drove oil temperature up to ~265F in the pan.

And besides, I picked the 120C number just to illustrate. The required temperature offset would be about the same if I had picked 100C.