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Another Oil Question........

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Being that I just purchased my 99' C2 with 19k on the odometer, I wanted to have the oil changed ASAP. It had been changed by a local dealer at 11k miles. My local dealer wanted to use Castrol Syntec (5-40 perhaps), but I've always favored Mobil-1. They said I could bring my own oil (great!) and they'd give a discount (great!). However, since I don't have an owner's manual for the car (see my other post), I was not sure of the weight. So I called the service rep from the auto parts store, he puts me on hold, and checked with someone. He comes back on the line and says to buy 5-30W Mobil-1, which I did. They then did the change with that oil a couple of weeks ago.

Yesterday, I notice an oil DIY by Loren (of course) which says 0-40w, 5-40w, or 5-50w.

"The list is now very long (for worldwide coverage). Here is a short list of popular oils (US/Canada):

Castrol Syntec 5W-50 5W-50 ncp G

Castrol Syntec 5W-40 5W-40 ncp GL

Mobil 1 0W-40 ncp GL

Mobil 1 5W-40 ncp GL

Mobil 1 5W-50 ncp GL

Mobil 1 Tri-Synthetic Formula OW-40 ncp GL

Texaco Havoline Synthetic 5W-40 ncp GL

Note: ncp oils are synthetic (or "non-conventional processing") oils. GL oils have good light running properties because of their light low-temperature viscosity as well as a high level of temperature stability. G rated oils can be used as non-seasonal oil, but do not have the same light running properties as "GL" oils."

Yikes! :o What have I done to my baby??? :help:

Question is, do I need to pull out that oil, filter, etc. ASAP, or am I ok for a while? I live in Tampa, FL, with the weather in the high 80s at present and slowly getting colder (maybe 60s by the end of November - Brrrr!).




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Changing the oil in a 996 is a 15 minute job (except for the drain and drip time). Porsche does not recommend a 30W oil for their cars.

With that said you are likely okay until your next oil change as long as the temps don't get into the 90's. For your climate you could go with any of the 5W-50 without a problem - but any of the oils on the list should be okay. Before this service bulletin came out Porsche recommended only Mobil 1 15W-50 for our cars. That is what is in my car right now.

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I'm afraid you need to change your oil straight away, otherwise you risk damanging your engine, and not just at high outside temperatures.

The problem is not so much the oil weight, but what we call HTHS (High Temperature High Shear) viscosity. HTHS gives you an indication when the oil film will break down and is therefore much more of an indication of the oil's suitability than the oil weight (the two are related in that higher weight oil will generally have a higher HTHS viscosity). Normal engines such as Porsche need an HTHS viscosity of at least 3.6 mPa·s. There are some very fuel-efficient engines that work on 2.9mPa·s.

Anyway, I just checked the Mobil website and Mobil 1 5W-30 has only 3.08 mPa·s, which is too low for Porsche engines. HTHS isn't always listed, but another good indicator is compliance with ACEA A3, which is the European Oil Standard that Porsche recommends for its engines. Mobil 1 5W-30 only complies with ACEA A1 and A5, but not A3 (again A1 and A5 are standards for special fuel-efficient engines). Mobil 1 0W-40 is fine, it has an HTHS viscosity of 3.6 mPa·s and complies with ACEA A3, and so is Mobil 1 15W-50 with 5.11 mPa·s.

(NB: it is perhaps worth noting that 15W-50 is not necessarily superior to 0W-40 just because it's got a higher HTHS viscosity. It's not the more the merrier, once you're at 3.6 mPa·s, you're fine. 15W-50 has a higher dynamic viscosity than 0W-40 which give it somewhat inferior cold start properties. That might not be much of a problem in Florida :D :D :D )



Edited by umn
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Thanks all. I probably knew the answer to my question deep down inside. It peeves me that the dealer told me the wrong weight oil to buy. :censored:

In any event, I bought 0-40w Mobil 1 today and did the oil change myself. I can't believe I paid the dealer close to $200 for that quick a job. It's easier than any car I've ever owned. Realistically, I paid the dealer so I could obtain the stamp in the service book for resale purposes later.

The only difficult part was getting the oil filter cover off. I had drained all of the oil before I set out to find a filter removal tool. The oil filter wrench I had was lame (and cheap to begin with). It didn't work. So I went to the dealer, but they didn't sell the metal cup type remover. "We don't sell tools". I went to Napa and bought 3 different sizes (I didn't know which fit). All were wrong and I couldn't get the filter loose. As is common, my sons were watching my struggles. Just when I gave up and said back to the store, my 12 year old son said "Dad, what about the Craftsman rubber strap wrench you got last Christmas". "No, son, that won't work, it just doesn't grip well enough". Well, I relented (partially to show him Dad knows what he is doing, and the wrench won't work). You guessed it, it turned, and off it came. My son was so proud of himself that he solved a problem which Dad couldn't.

So two good things came out of this: (1) I'll never pay the dealer to change the oil again; and (2) through my hardheadedness (is that a word?) my son gained some mechanical confidence, and his creativity was rewarded. The prior is nice, but the later is priceless. :thumbup:

Thanks again.


p.s., I believe I found the correct size oil filter cup type remover at Autozone, and for less money than Napa. Autozone is the same place I found tamper proof torx bits (again, less than Napa).

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If you look up the wrench for a Porsche 944, that wrench fits our plastic oil filter cannister. It is about 74-75mm with 14 flats. Some guys I know don't use a wrench as they can get it on and off by hand.

It seems like every few months Porsche issues another approved oil bulletin that takes off previously approved oils and adds oils that had not been approved.

Like Loren, I use Mobil One 15W-50, in my 1997 Boxster. This oil had been approved for years. Then Porsche deleted it in a 2001 bulletin and it is still off the list with the most current bulletin that came out a few months ago. I have changed my oil twice with 15W-50 after it went off the list and see no reason to use anything else after 7 years.

Mobil One 5W-30 was approved in a March 2000 bulletin for the 996, and also the Boxster. Now it is not.

15W-50 was approved, now it is not, but 5W-50 is. Not a big difference to me in sunny California. I always thought it was to get better fuel economy ratings and/or to reduce customer complaints about valve lifter noise.

At one time a few years ago Porsche recommended a Mobil weight we could not buy in the US and guys were mixing different weight oils to get it. Funny stuff when it comes to oil.

Umn has some interesting info and some of the oil bulletins do reference this ACEA A3 specification. I wonder if this specification was around when the 2 oils I mentioned were on the approved list. Jeff

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Umn has some interesting info and some of the oil bulletins do reference this ACEA A3 specification.  I wonder if this specification was around when the 2 oils I mentioned were on the approved list.


Hi Jeff,

ACEA A3 has been around since 1996. Before that we had CCMC G5, which was quite similar. FWIW, here are the ACEA specs:

ACEA European Oil Sequences

I hope I didn't bore you guys with too much technical detail. I guess the only point I wanted to get across is that these days there is a proliferation of engine oil types and you have to go into quite a bit of detail to be able to tell if a certain oil is right for your engine or not. Use oil that's on the OEM's approved list and you are safe.

I guess the reason why some oils appear and disappear on the list is this: In order for an oil to become Porsche approved, it has to comply with ACEA A3 and be run by Porsche on an M96/03 test rig. I think Porsche charges the oil manufacturer about 40,000 Euros for this, but the approval is only valid for as long as the oil composition stays within certain parameters. If an oil disappears from the list, it might be because the oil manufacturer has changed (updated) the oil but chosen not the re-run the test. Don't know for sure though.



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There must be a cd for other models. I'll ask.

I think the cd is only given to people who buy the car. It is a PNA not PAG cd. I saw them in the in the manager's back office so it is nothing they just hand out. Also saw someone on ebay selling one (or a copy) for $25.

I bet no customer has seen this binder.


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