eclou

Having just changed my oil, I am now wondering if I should have used 5W-50 instead of 0W-40. The manual says either.

AIravani

Eclou, how many miles are you at? Did you change your oil or did a Dealer/shop do it?

1999Porsche911

I seldom comment on oil, however, if you want to encourage leaks, oil burning and improper hydraulic acition of the valvetrain then you should use 0W40. If you want better engine protection, faster valve response, better sealing and less oil burning, then I would suggest nothing less than a 5W oil in ANY engine that is not run in sub ZERO temps, regularly. All my high compression engines run 15W50.

eclou

A 0W-40 oil should provide the equivalent of a 40W vs 15W-50 providing the equivalent to a 50W oil at operating temps. The 0W-40 should provide the equivalent of a 0W vs 15W-50 providing the equivalent to a 15W at start-up. I run 15W-50 in my track cars but usually run lighter oils in my newer cars - tolerances on the newer vehicles are going to be tighter. GM cars like your Z06 are recommended 5W-30 IIRC. My main concern is protection of the turbos which in the 997TT run oil and water cooled centers. Not sure if one vs the other will be more resistant to coking. I guess I need to look up the flash burning temp data

1999Porsche911

I have read the above 15 times and I have no idea what you said.

IMO, 0W is too thin when cold and 40 for the high viscosity protection is too thin in high compression, hot running engines.

eclou

At running temps, 0W40 is 40W. 15W50 is 50W.
At startup 0W40 is 0W. 15W50 is 15W.

It is advantageous to have a thinner oil at startup to ensure that the top end gets pressurized more quickly. When I ran straight 40W in my old street rods, it would take a few minutes for enough oil to reach the lifters and quiet down the valvetrain. 0W should be better than 15W in that regard, but probably not a huge difference.

texas911

0W-40.

eclou

I'm at roughly 2500 miles, did it myself.

1999Porsche911

That is not true. (BTW: the W indicator is only for cold viscosity). The number before the W is it's flow rate NOT UNDER PRESSURE) at 0F. The second number, without the W is it's flow rate at 212F.

Under pressure, especially using a positive displacement oil pump, the flow of a 15W and a 0W oil is virtualy the same at 20F, so unless you start your engine in a temperature less than 20F, there is no flow benefit to using 0W. However, because the non pressurized flow rate of the 0W is greater than a 15W oil as it begins to cool, you lose more oil film on engine parts and oil in the lifers, etc, with the 0W simply because of gravity. That is why, many engines that sit with a thin oil for several days will make lifter noises more than engines that have a thicker oil.

Now, the second number of 40 and 50 is the oil's flow when the oil is at 212F, with the 40 flowing faster and the 50 flowing slower. If you never get the oil temperature above 212F, then you statement is correct, but you would be living in la la land if you do not think you oil gets hotter than that.

Now, we all know how oil is partially used to help cool the engine and we all know that the speed at which the oil flows greatly effects how much heat is transferred to it. If it is too fast, less heat will be transferred to it. If oil is less dense, the heat transfer will also be less.

An example would be moving you finger quickly over a the flame of a candle. No problem and your finger is not burned. Slow your movement down and the amount of heat absorbed by your flesh will increase as the speed decreases.

Film thickness is also important in a hot engine and when your oil starts getting 220F+, crank journals, etc, greatly appreciate the 50 weight oil.

There are many sides to this argument, but personally, I would never subject a car I cared about to a 0W oil in temps above ZERO.

AIravani

Eclou did you drain the turbos as well, and can I ask why you changed so early. Do you do a lot of track runs with the 997tt? Also was wondering the total # of quarts you poured in.

eclou

I did not drain the turbos, nor did I change the filter. I have always done a break-in oil change within 1k miles. I waited until now since I figure the crankcase was filled with syn from the factory and that lengthens the supposed time for ring sealing and seating. I put in about 8 qts


With regards to the weights, I check the Mobil 1 site and 0W40 is listed as having a flash point of 236C (456F) vs 230C(446F) for 15w50. Pour point for 0W40 is -54C and for 15w50 is -45C. 0W40 is also listed as being Porsche approved whereas 15w50 is not. Leaning towards keeping the 0W40 if the protection is going to be comparable since it should also lead to less internal drag and better performance.

1999Porsche911

Well then, I guess if you are starting your engine with the oil temp below -50F then you should use 0W oil. Flashpoint has nothing to do with an oil's viscosity or lubrication properties. Oil condition would be the last thing to worry about if your oil got even near those tempertures.

Mobil has a pretty good marketing department to maintain such an unbiased website, don't they?

Well, you asked and have now been warned against using 0W40 in your turbo for the best protection. Best of luck to you. Keep us posted on how much oil you burn, drip, or otherwise can't find.

Ahhh, MARKETING. Creates facts out of garbage. How are the people in the Midwest handling the Global Warming effect these days?

eclou

I am pretty certain that the turbo housing is going to get much hotter than 212F. Coking is the main issue and thus flash point is going to be important.


You know the old adage about a porsche that's not leaking oil?

1999Porsche911

Is it something like " Amara's Law " ?

gota911

That's the best one I have heard all week!