Originally Posted By: Trav
Originally Posted By: CATERHAM
Originally Posted By: Zaedock
Originally Posted By: CATERHAM
And how else are you going to determine the operational viscosity of an oil in a given application? You can't without gauges.
The following chart from Joe Gibbs Racing discusses the subject matter:
http://www.drivenracingoil.com/dro/viscosity
I didn't say gauges were not important. I'm simply correcting you in that using OP/OT to determine optimal viscosity for every engine is wrong and very Haas of you.
Your bearings could very well do fine on a thin oil, but given Trav's example, may be wiped due to crank flex under shock load where the OP and OT are still "OK". This doesn't even touch on other engine areas like timing chains, timing gears or valvetrain requirements where a lower HTHS oil may appear fine in the bearings, but not properly lubricate these components under ALL conditions.
That's funny "very Haas of you".
One area where I disagree with Dr. Haas does apply to the importance of HTHSV or specifically the HTHSV rating methodology.
HTHSV correlates with oil pressure and I wrote a piece about it:
http://wwwo.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2276634&page=1
In determining the minimum viscosity requirements of an engine shock loads must of course be included. Naturally one must know what minimum OP value that represents. Since viscosity is a function of oil temperature, the grade of oil required and therefore the HTHSV rating of the oil required to maintain that minimum OP in temperature related.
That's why you can run a 800 HP NASCAR Sprint engine on a 1.7cP HTHSV 5wt qualifying oil for a few laps as long as the engine oil doesn't get above a predetermined maximum temperature.
Originally Posted By: Caterham
In determining the minimum viscosity requirements of an engine shock loads must of course be included. Naturally one must know what minimum OP value that represents. Since viscosity is a function of oil temperature, the grade of oil required and therefore the HTHSV rating of the oil required to maintain that minimum OP in temperature related.
That's why you can run a 800 HP NASCAR Sprint engine on a 1.7cP HTHSV 5wt qualifying oil for a few laps as long as the engine oil doesn't get above a predetermined maximum temperature.
NASCAR engines have no problem with low viscosity oils they have a super rigid block and crank and very close clearance bearings with big fat journals, the only think old school about these engines is they are V8's but that about it. These engines are purpose "built" for low viscosity oils so why would they have any issues?
Here is the problem i have with using gauges as a primary vehicle for determining optimal oil viscosity.
Its true that on a normal mundane daily grocery getter most of my argument is somewhat irrelevant but whenever the HP numbers and the level of engine abuse rises my argument becomes very relevant IMO.
Once engine HP reaches a certain point the block and crank rigidity play a much more important role in keeping the bearings alive.
The oil pressure gauge port may not even realize a millisecond drop in pressure from the oil film being broken by a mechanical collision between crank and main bearing.
At best it would probably be a slight needle variation that would probably go completely unnoticed. At worst the gauge does nothing at all.
IMHO from my own observations and technical data on the engines over the last 15 years they fall basically into 2 camps. They can both utilize lower and higher viscosity oils as they are both world engines.
Lets keep it simple and call them Japanese and American engines because they seem to fall into these camps easier than say German, Italian or French.
They all use a bearing with enough clearance to utilize a multitude of viscosities but the Japanese built the engines closer to being a purpose built low viscosity oil engine.
Their engines use rigid block and high grade well supported cranks basically eliminating crank flex or block distortion from the equation.
Now the American manufacturers like Ford liked the idea of better fuel economy and free HP so they jumped on the bandwagon. The problem is their engines was essentially "old school" including the original modulars.
In light use they could "get away" with 20w but knew that at some point crank flex was going to come into play either from the cast crank or block distortion.
Either one of these conditions can come from either of two areas, high RPM or high torque loads.
Their answer to this was to place a GVW proviso on some engines being back spec'd. They later made slight improvement and were able to utilize lower viscosity oils to their full extent.
GM and others didn't go this route. Their engines were closer to old school engines, cast cranks and not so rigid blocks. Larger bearing clearances and old style oil pumps almost demand they use a higher viscosity.
Even their High HP engines that did use a forged crank and 4 bolt mains were built somewhat "loose" in the old school HP engine building fashion. It doesn't make their engines any worse or any better.
All companies are now moving in the low viscosity direction and rightfully so, there are a lot of advantages and very few if any disadvantages other than needing a very high quality oil that may cost more.
IMO Claiming oil pressure and temp gauges can be used in selecting the lowest working viscosity oil in an engine is a fools errand.
I have seen posted that PP 5w-30 is preferable to PU 5w-30 solely because its thinner, this may not be true at all. The engine requiring the xw-30 were not built with low viscosity oils in mind and are constructed accordingly.
Just my take on it. Caterham you have presented a lot of valid arguments for lower viscosity oils i wont deny that but i believe i have some valid point here.
I think you're over thinking this.
Taking a step back, I think we can agree that for any application there is minimum viscosity (operational) that is required for how an engine is being operated be that harshly or gentle; the former
requiring a higher viscosity safety cushion.
Through various means that viscosity safety cushion, not the oil grade but the actual minimum viscosity in cP, can be established.
One function of an oil pressure gauge is that it an effective viscosity meter, consequently it is not hard to establish a minimum OP reading that corresponds to the previously established
safe minimum operational viscosity for an engine operating under harsh conditions.
Once that minimum OP reading is known then one can determine what oil grade (specific oil viscosity) is suitable taking into consideration expected maximum oil temperatures and other secondary factors such as oil shear and fuel dilution that will affect an oils viscosity in service.
Saying that you can't run a 2.6cP 20wt oil (or even something lighter) in an engine implies that you can't maintain adequate OP. Because if you can maintain the previously established safe minimum OP then by definition you are maintaining an adequate operational oil viscosity. The grade itself is of no importance as the engine can't tell what it is. It could be a 60wt oil at 150C oil temp's or a 20wt at 90C, the operational viscosity could be identical.
With the prices of fully synthetic oil being so low nowadays, there is no reason to overlook their multitude of benefits in an engine that doesn't burn oil.
