Oil thread! But let's talk about shearing!

Disclaimer: If you're just going to complain about another oil thread, GTFO. I'm trying to generate discussion here. TIA! I'm currently running M1 5w-40 in my 40th Anniversary. It's time for an oil change, and I was looking at various options. Based on reading the forums, it seems that these motors generate a lot of heat when run hard (eg, 20min DE sessions). My concern is shearing of the oil during hard driving. Does anyone have any information in terms of oil shearing due to high heat usage? (wish there was a built in oil temp gauge!) I'm thinking Mobile1 5w-50 may be the way to go. If it shears down, hopefully it'll shear down to a 40w or so. Vs. a 5w-40 shearing down to a 30w or something. Unless there exist a "heavier" weight 5w-40 out there that is a quality oil. (Think of the green castrol that was 0w-30 but was basically a 40w oil) Thanks!

G'Day Sport...Is this what you are talking about? http://www.youtube.com/watch?v=N7r1gN0vYfw

Quotes source post: 10881929

A considerable amount of heat is generated by the oil from hydraulic friction. The thinner oil not only heats up less but flows more readily and thus carries heat away from the bearing. A thicker oil might actually be hotter in the bearings than a thinner oil and the thinner oil thus less prone to high temperature sheering simply because it runs cooler and is better able to carry the heat away. If you want to run an oil with a high(er) HTHS number than what Mobil 1 0w-40 provides then make a list of approved oils -- or any oils if you do not care to stay on the approved oils reservation -- and pick one that offers the highest HTHS number. However, you do not know how long that number will be in effect when the oil is in use. If you venture off the approved oils reservation in your focus on HTHS you may select an oil that is sub par in other areas. To point out the obvious the engine spends a lot of time running under conditions in which the HTHS number does not even come into play. IOWs, so far your engine has not apparently suffered from any shortage of HTHS protection which suggests the HTHS protection it is receiving is quite good. Good when the oil is fresh. And good right up until you drain it and replace it. But you want to improve this area that hasn't been a problem. So the risk is in moving to an oil that offers even more HTHS protection you select an oil that is lacking in other areas.

Let�s look at the system holistically. We have a gear pump (a.k.a. oil pump) driven off the crankshaft. Its discharge is connected to a complex lubrication system distributing filtered oil under pressure to main bearings, camshafts, valves, turbos (where applicable), etc. Its suction is connected to the �integrated� oil sump that collects oil returning from the above components. The gear pump will pump oil regardless of its viscosity (within limits of course). It just �cuts� chunks of oil and shoves it into discharge galleries under pressure at the expense of engine HP. In fact it operates more efficiently (less oil slip) in thicker oil environment. The lubrication system however creates backpressure that is reverse proportional to oil temperature. These two systems should always balance i.e. both curves will cross at one point. The Pump curve will remain relatively stable and the system curve will obviously float with actual oil temperature. There are of course other components, such as oil filter and bypass valve that keep oil filtered, prevent the system from over pressurizing under high RPM�s and allow thick cold oil flow in case oil filter creates too great a differential pressure across its filtering element. Now we go racing or DE driving. Your oil sees temperature excursions to 250-275*F. A few things happen at this point. One, oil thins down to below designed viscosity (for XW-40 the range is 12.5 � 16.3 cSt). There is direct correlation between KV @100*C and HTHS. Both will trend in the same fashion. There is another important direct correlation between Mean Oil Film Thickness (MOFT) and HTHS. In other words you are losing protection offered by 40 grade oil down to 30 grade or even less in extreme situations. More importantly all Viscosity Improves (polymers = plastics) shear permanently causing sludge and permanent viscosity loss. Also oil exposed to excessive temperatures will eventually oxidize causing permanent chemical change to the base oil molecules. Imagine oxidation as less severe combustion process. At this point your oil system pumps oil at higher rates due to reduced resistance (viscosity) which is not a bad thing. Your film strength however has been reduced as well. Your bearings may be OK as long as oil maintains adequate hydrodynamic lubrication. Your piston / ring / cylinder wall area gets much more severely affected as it typically operates in mixed or boundary type of lubrication to start with. The lubricating conditions get much worse with loss of HTHS at elevated temperatures. Google Stribeck curve to see what we are talking about. In other words what I am saying is that we want to bring this system back to its balance as it was at 200*F. And the only way to get it back (without reducing oil temperature) is to ensure that your racing oil�s operating viscosity at say 250*F is about the same as your DD oil at 200*F. The next step would be to choose a group V ester based oil that will have minimal amount of VI�s and will withstand elevated temperatures much better than HC or PAO based oils. That wheel has been invented and it�s called Racing Oils. Several brands come to my mind, but I will leave it up to you to pick your favorite one. Last but not least, I would look at mechanical ways to improve dissipation of increased amounts of heat such as additional heat exchangers and/or LT thermostats. Sorry for a lengthy write-up. These issues are very complex and we just scratched the surface. Always open for more comments. Cheers, =L=

Last I heard this thing called a combustion engine was nothing new and this thing called oil wasn't either. I've heard that cars could go a million miles on synthetic oil without exhibiting any real bad wear or breakdown(under controlled laboratory conditions of course). I heard there's a lot noise on these forums that the world will be ending soon...

Don't they run Mobil 1 in cup cars ? I don't think a 20 min de session on relatively fresh oil is going to cause you issues. If you want " insurance" just change your oil after the de. For extra insurance do a uoa before and after the de. m1 is relatively cheap. If you want to try redline or other full pao oil experiment run a similar uoa before and after a de to see if there is any difference.i 've still yet to read a thread where anyone had premature wear using m1. Key is As long as it is changed frequently.

http://www.mobil1.com.au/performance/miles.aspx