1999Porsche911

That is why I suggest you try the easiest approach fiirst.

utkinpol

BTW I spoke to mechanic in local Porsche tuning shop I use all the time, and his opinion is that 15w50 oil should not be used as it is too thick for most hydraulics engine internals and he says I should never use oil thicker than 5W-50.

He says he would rather recommend doing oil pan extension kit ($289 one) but this X51 996 should also fit fine and it makes sense to do this but adding that oil pan spacer would help most.

1999Porsche911

Really? Ask your mechanic why a Porsche approved 5W50 oil will work fine with the hydraulics but a 15W50 oil will not, even though they are the same viscosity?

He obviously knows little about oil.

utkinpol

Owning Porsche pro shop for more than 15 years he knows a bit I guess. In MA as it gets colder than during summer time 15w50 mobil is too thick for 996/997 engine as he says. For what`s it worth I see no reason not to trust him.

BTW in Porsche official approved oils list there are plenty of 5w50 oils and not a single 15w50. It also makes me think there is something there about it.

1999Porsche911

WOW! He owns a Porsche PRO shop and not just a Porshce Shop.!

So, I ask once again: What is the difference in kinematic viscosity between a 5W50 oil and a 15W50 oil? Also ask your mechanic how Porsche approved and factory filled 15W50 worked for more than 20 years and now doesn't work in those same engines if you base "working" on what is on the approved list..

I am amazed that someone blindly trusts someone else just because they own an autoshop. My moto: Distrust until verified. Especially true when claims go against even the most common of common sense, let alone science.

Remember, many people exaggerate to prove their point. This includes you when you state "BTW, in Porsche official approved oils list there are plenty of 5w50 oils ...". Please define "plenty".

15W50 provides all the protection you need to temperatures below 0F. Mobil 15W50 (as well as many other oils) provides better absolute viscosity, which is the only viscosity that matters on a running engine.

These facts are easily verified by anyone willing to do a little reading for themselves. Look at the requirements from the SAE on how motor oil viscosity must be determined. Also read about determining the HTHS Viscosity of the oil and you'll clearly see why one is more important than the other.

jrgordonsenior

I've used 15/50 in all my race cars especially in the warmer months. Just let it warm up sufficiently to get circulated...

utkinpol

My car is DD and I run it even now occasionally when temperatures are close to single digits. I just keep her inside when there is too much snow/salt out there. so going with thicker oil is not a best option for colder months IMHO.

For summer time I will consider this advice if issue will repeat itself. It would be great if simple oil viscosity adjustment would remedy this issue with air in valve lifters but I am a bit skeptical about this. Will see.

1999Porsche911

It's currently 0F here and I just took the 996 for a ride with 15W50 oil in it. A 15W oil provides protecton at cold start all the way down to -10F. Additionally, once warm, your engine temperature is just about as hot as it will be on a 100F day.

Fahrer

The difference between a 15W50 and 5W50 oil is that the 15W is a higher viscosity base oil ( synthetic or mineral) at 32F. In order for a lower base stock to have the same viscosity as the higher viscosity oil at elevated temperatures, viscosity index improvers are used. These VI improvers are basically polymers, typically ethylene-propylene types, and are relatively stable. These disolved polymers help keep the viscosity of the 5W base stock from falling to the level of the 5W at the elevted temperature ( approx. 200F). It simply falls to the level of a 15W base stock at the elevated temp. The wider the spread between the higher and lower number, the more VI improver used. It is possible for the VI improver polymers to experience shear and result in a somewhat lower viscosity at elelvated temprature. I would say that the 15W might be a bit more stable under severe conditions but not for normal road use. On the track, with high ambient temperatures, may be more of a factor.

1999Porsche911

So, if both 5W50 and 15W50 have the same viscosity at operating temperature, why is 5W50 better for street driving than 15W50? I fail to see the logic of your explaination. Additionally, the marketting viscosity rating is such a small part of choosing the right oil. The protection fron shearing, which is what keeps parts from touching, is far greater in the 15W50 than the 5W50 as are the anti-wear compounds. Unless you are parking your car in climate below 0F, there is no need to run an oil rated less than 15W.

Fahrer

You are missing the whole point of multi-viscosty oils. Even at 70F, a 5W or 0W will lubricate better at startup. With day-to-day startups (and primarily when it is cold out) you have much better lubrication and for many cars, no need to change oil types from one season to the other. The shear I refer to is the shearing of the polymer molecules which would reduce the impact of the VI improver. Your statement regarding the 15W50 vs. the 5W50 at high temperatures is untrue unless the polymere has broken down. Besides, it is the extreme pressure additive ( ZDDP) that is more of a factor for cam and bearing surfaces. Theses two oils will perform similarly at elevated temperatures and the 5W will lubricate better at lower tempertures.

Fahrer

After a quick google I found this.

There are much better articles than this one but is shows the impact of VI improvers FWIW.

mysite.verizon.net/oldhokie/windyridge/oil.pdf

1999Porsche911

Whoa! A 5W50 oil does not have better lubrication at 70F than a 15W50 oil does. I assume you are defining lubrication as the ability to flow. Remember, the kinematic viscosity rating has nothing to do with the flow rate of the oil under pressure. Both oils will flow exactly the same speed in your engine at 70F. However, the 15W50 oil will remain on engine components much longer after shutdown than will the 5W50, providing added protection between parts at startup..

Secondly, look at the specs of the Mobil 5W50 and 15W50 oils. As I stated, their 15W50 has a much higher shear resistance. 16% more.

As for ZDDP: You ever hear any ticking in your engine from the valve train? Wouldn't it be nice ff that ticking was custioned by a little ZDDP? That is, unless you don't thing that there is any "extreme pressure" between the cam lobes and the lifters or other parts of the engine.

ADias

Careful using high viscosity low temp numbers such as 15WX. I am told that variocam plus parts do not like that...

1999Porsche911

Yeah, people love to keep repeating popular beliefs no matter how untrue they are.