What Weight Oil
 

Do you use and why?

-Alex

Stick with 5w-20 or maybe 0w-20. Most wear occurs at startup all oils are to thick upon start up to properly lubricate. Oil at operating temp are pretty much the same density.

I am running 5w30, most likely might switch to 10w40, I am running a paxton though.

Why 40?

I am presenting the question because recently I called Westway and asked the service department what oil to use and they said 5W30. I didn't pay attention to the factory oil cap before calling so wondered why they would advise of something different.

-Alex

Joe Gibbs 0W. Because it is fast.

Pretty gd oil right there and gd weigh choice.

I was considering that, mainly to avoid any potential powertrain warranty disputes.

-Alex

Interestingly enough the Track Pack specifies like 20w-50. WHy IDK.

The thickness of moving oil is measured in centiStokes or cS. Most engines want the oil viscosity to be around 10 cS at normal operating temperature. The really thick multi-grade oils have a viscosity of 20 cS at operating temperature. One is not twice as thick as the other, it is only 10 cS thicker.

As we increase the heat from 212°F to 302°F the most commonly recommended oil thins from 10 cS to 3 cS. The thicker oil drops from 20 cS to 4 cS. Note that in a very hot engine the difference between the two oils is now only 1 – 2 cS. In other words they have about the same thickness. There is little advantage to a thicker based oil as a 20W-50 at very high temperatures. No, the 4 cS oil is not twice as thick as the 2 or 3 cS oil. This difference is almost insignificant.

The thing is most wear occurs at startup. All oils are to thick at startup to lubricate properly. As they heat up they all thin out to about the same specs.

The best way to figure out what viscosity of oil you need is to drive the car in the conditions you will use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those circumstances. For some reason very few people are able to get this simple principal correct.

Very informative post, thank you. I don't think most people knew all of that information. In these cars it is impossible though, to figure out what oil pressure we have since the factory gauge doesn't give a reading in measurements of PSi... or any measurement for that matter. So we are forced to get an aftermarket gauge. But that's another topic all together.

I do have to ask though about the 10psi/1k rpm ratio. At operating temps at idle I would read 30psi at 800rpms with the LS1 using 5W30. With my 7MGTE at idle using 20W50 it would read just under 40lbs at 1,000rpm as shown here. Ignore the OU flip flops.
http://i80.photobucket.com/albums/j1...a/DSCF1202.jpg

So do you mean 10psi per 1,000rpm above idle?

-Alex

Exactly. So at 7000k rpm you'd want about 70 psi plus or minus. Ferrari uses a pricnicple of 75 psi at 6k rpm. I feel that that is a pretty gd measuring stick.Some people have tried this and occasionally get a somewhat low oil pressure while at idle. This is fine. There is no stress on parts at idle, the smallest oil flow will do the trick. It is at higher RPM where more BHP is produced.
The temperature of oil on your gauge is not as hot as it really gets. This temperature is an average with oil from different parts of the motor. Some parts are hotter than others. It is said that some of the oil gets as hot as 400° or 500°F in these racing situations.
Since the oil with a viscosity of 10 cS at 212°F thins to a viscosity of 3 cS at 302°F we will get more flow. The pressure will go down some as well. This is OK as long as we have a minimum of pressure to move the oil.

This increased flow will result in increased cooling by the oil. This is a good thing. You would probably want more oil flow in these situations and you get it. The hotter oil thins and this increases flow. The higher flow works harder to separate the engine parts that are under very high stress. It all works out for the better. Higher revving engines need thinner oils. You do not necessarily need to go to a thicker oil while racing. Only experimentation will tell.

Here's a picture of the LS1 at idle and at 25mph. This is with the digital gauges but, you get the point. Each bar for the psi represents 10psi. Sorry for crappy pics.

http://i80.photobucket.com/albums/j1...s/HPIM1707.jpg
http://i80.photobucket.com/albums/j1...s/HPIM1705.jpg

-Alex

Ah, very good to consider, had not thought about that. Guessing that is especially true for the oil going through the turbo.

-Alex

40 psi at 25 mph is pretty nice. Oil may be a little thick but its ok.

Probally even more extreme!!

The reality is that motor oils do not need to be changed because they thin with use. It is the eventual thickening that limits the time you may keep oil in your engine. The limit is both time itself (with no motor use) and/or mileage use. The storage of motor oil in your garage, particularly mineral based oils, slowly ages the oil limiting its use later. Do not store huge volumes of oil in your garage that is exposed to extremes of temperature.

Increasing the pressure while using the same oil will increase the oil flow but increasing the pressure by increasing the oil thickness will result in less flow. It takes more pressure to move a thicker oil. When you go to a thicker oil the pressure goes up because of the increased resistance, and therefore reduction of flow. Because the pressure is higher sooner, the relief valve cuts in sooner. Flow will actually be less when the RPM is up and the flow is needed the most.

10-20 psi at idle would scare the shit out of most people. LOL