Hey guys,

So I noticed the last time I drove the 996tt that the engine oil level was only 2 bars above minimum and I wanted to get some oil. Unfortunately, I didn't have access to the previous owner's spreadsheet on oil consumption and thought he used M1 5w-40 TDT so I picked up a few quarts of it. He actually used Castrol Syntec 5w-40. Before I run out to grab a few quarts of that, I started thinking if I could just throw in the M1 TDT and mix the brands. Any thoughts or experiences on this? The grades are the same, just different companies, as well as the fact that the M1 is the TDT. Thanks.

 

That should be fine. You mainly want to ensure the low-temp viscosity doesn't
get too high. Any top quality synthetic 5-40 should be fine.

And note that oil is cheap, and oil consumption is *not* something to be
'tuned for'. A motor that burns some oil may well still be healthier and last
longer with the recommended viscosity rather than with running a thick
oil, just to provide the false comfort that 'something got fixed' when the
observed consumption went down.

 

Never mix oil brands or even types within a brand for OTHER THAT EMERGENCY USE.

Different oils MAY have different stabilizer chemistries which do not have the same long term actions.

It is universally accepted that you can 'top off' with almost any oil- that is better than running low- but most will then recommend that you change to a fresh fill (of one oil) as soon as practicable.

 

Plus one..

 

As long as the viscosities are within the specified range, the additives will continue
to function according to their design in the quantities/percentages that exist in the
mix. There are no oil additives that are mutually exclusive, such that mixing oil A
with additive XYZ will be bad if mixed with oil B with additive DEF. If you mix two
top-quality oils, your combined additive package is likely to be just as good. In fact
some folks utilize the fact that additives are linear in their effects (according to
percentage) whereas viscosity in logarithmic (adding a little thin oil to a lot of
thick oil has a big effect, thinning the mix quite a lot, whereas on the other hand,
if you want to thicken a mixture, you have to essentially overwhelm volume of the
the mix with thick oil before it gets a lot thicker.) This can be taken advantage of
if you need to run a thin oil, but the thin oil doesn't have as much of an additive
that you'd like, eg: ZDDP. If you have a thicker oil with lots of ZDDP, you can run
50% thin and 50% thick by volume, and get at least 1/2 the ZDDP by volume, and
the mix viscosity will still be close to the original thin oil.

Tons to read and search at http://www.bobistheoilguy.com

Even within a given oil brand the additive package will differ,
sometimes significantly between types and even just viscosities
of their oil, so mixing within a brand is no more chaste an act
than across quality brands.
HTH,
Joe

 

BITOG is a GREAT site for oil questions, so I will not re-hash it here....

Much respect Joe, but I think it is bad advice to simply say 'any mixing of all oils is fine'.

I will agree that it CAN be done, but it is a science beyond the scope of internet forums. IMO

A

 

I didn't say 'all', I specified synthetic top quality oils of like/allowed viscosity.
Much respect to you too! I would be very interested to hear of technical
details anyone might know/find as to why/when it might not be OK.
Regards,
Joe

 

Your advice regarding mixing oils is wrong.

Based on the info I have from a Porsche Approved Oils list dated 4/15/2010, first only approved oils should be used.

Mobil 1 5w-40 TDT oil is not approved for use in Porsche gas engines, not even in its diesel engines.

Porsche approved oils will have A40 somewhere on their label.

Only oils that are Porsche approved are miscible. That is if one wanted to switch from one approved oil to another there is no need to flush the engine to remove the previous oil.

However, Porsche goes on to say it recommends that if the oil needs topping up to use the same oil as is currently in the engine, if at all possible.

Sincerely,

Macster.

 

From what I understand, there's no urgency to top off if you're 2 notches above minimum. Some Porsche mechanics don't fill the oil past half way between min and max line. Still plenty of oil at the min line -- better to be low than high is what I've heard and read. Anyone else confirm?

 

While it is true the engine or in the case of the Turbo the oil tank still has considerable oil in it even with the oil level down to just 2 bars above min, it is not a good idea to run the oil level that low.

Under some driving conditions (granted maybe extreme) this low an oil level could run the risk of the engine oil pump ingesting a bit of air (or more accurately, oil that has some entrained air in it, IOWs, foamy oil) or even worse. Granted less likely with a dry sump oil system, but why risk it? Oil is cheap. A new engine? Not so much.

Also, one can get a big scare if he runs the oil level this low and then all of the sudden gets in the car and starts the engine or even while the engine is running sees the low oil level warning flash.

Really the oil level should be kept at mid-level or higher, but not above the max. line. The factory oil change instructions have the amount of oil added to the oil tank (7.8l with filter change IIRC) so that upon the oil level check done that the lower 7 segments of the oil level display are lit, so the oil level is at the max. line but not above it. Thus the factory 'likes' the engine full of oil, but not overfilled with oil.

So, this is where I'd try to keep the oil level. I write this with my Turbo's oil level showing 3 bars below the max. line. However the oil level was checked on a slight slope (off to right and down a bit at the rear of the car) so the oil level might still be at just 2 bars below the max line, where it was this AM before I left for work. But if I check it tonight at home and it is 3 bars low I'm adding enough oil to bring it back to the max line level.

Sincerely,

Macster.

 

Thanks Macster, but I think we will agree to disagree, based on your
rigid reliance on Porsche documents, and my being less so, based on
my technical understanding of the issue. I am certainly open to education
on the topic and would welcome any technical material that describes a
danger in using/mixing top-quality synthetics in the viscosities required,
but that have not yet been specifically approved by Porsche.

Joe

 

Will...not...post....

Must...resist....Oil Thread...must not...


ARRRAAGAGGGHHHH........

 

Why not rely upon the Porsche approved oils list? Why should I risk the health of my engine by treating it as an oil guinea pig by running the moving target of the oil du jour?

If I believed Porsche purposely excluded the best oil for whatever reason I would not be seeking out an oil I'd be seeking out another car from an automaker I could trust to know which oils are suited or not suited for use in its engines.

You know it may just be that Mobil knows some of its oils are not suitable for use in Porsches: Some Mobil oils are not on the approved oils list simply because they do not measure up to the standards Porsche has set. Maybe the absence of these supposedly superior oils from the approved list may be Mobil's doing and not Porsche's?

Which suggests the question how do *you* know the oils you are advising mixing are top quality synthetics and their mixing is not in some way harmful to the engine? Is your insight into oil chemistry, oil manufacturing, and blending superior to that of Porsche and perhaps even Mobil?

Or are you simply falling back on a rigid reliance that anything Porsche has to say on which oils are the right oils to use means just the opposite?

IOWs, approved oils are terrible because Porsche has listed them and unapproved oils are great because Porsche did not list them?

Furthermore, that you believe that these oils not on the list are great and the right oils to use simply because Mobil says they're great oils for some specific diesel engines and recommended in some non-specific terms for use in some gasoline engines?

I think you have some audacity to offer up your opinion regarding what oils Porsche owners can/should use and how they can blend/mix them which is quite contrary to what Porsche says.

Use whatever oil you want in your car's engine but I think you'd do the Porsche community a world of good by keeping your well-intentioned I'm sure but nevertheless misguided oil recommendations to yourself.

Sincerely,

Macster.

 

We are all entitled to our opinions. It is certainly a viable approach to follow
Porsche's recommendations, but I hope you are aware that they sometimes
change, and sometimes it is due to issues they first hear about from events
that happen in the field. They rightly react to reality as it presents itself after
their best efforts, so you are in fact an unwitting Guinna Pig as are we all, no
matter what path you choose. And I am not one who has any conspiratorial
fear of Porsche and oil companies colluding against our interests. I am just
comfortable with the science as I understand it, enough to make the choices I
have mentioned, in direct response to the OP's request for thoughts and
experiences.
I will try to answer your questions, but it seems puerile that you would claim
it to be audacious to offer requested thoughts and experiences.
Some Mobil oils are not suitable, and others are, and are recommended, and
yet others are, but are not recommended for other reasons such as emission
control reasons, even though they may be superior from a tribologist's point of
view, such as some of the nominal Mobil 'racing oils' that unlike real racing oils,
which are typically changed on a per event basis, have all the detergents and
anti-acid base content that one would expect for a passenger car duty cycle.
The issue is that they have more ZDDP than the EPA currently wants Mobil's
automobile offerings to have. Therefore, if ones concern is for maximum motor
protection, one may sometimes make an educated off-menu selection. Education
is key. Continuing education is best, so I am open to evidence that mixing as I
describe and do it, is bad. Your doctrinaire approach is defensible too, but the
stridency is inept.
Regards,
Joe

 

My 2 cents: Recommendations by Porsche does not mean no other product will work and work well. Don't even get me started on tires. The whole "N" rating is a joke.