1989 Porsche 928 S4: what oil at 100K?

What grade does the owners manual recommend for the climate that you drive the car in? Whatever that grade is, I'd use it.

The "extended performance" is just a re-labelling of good ol' Mobil 1. If its not available yet, do your next change with the correct grade of Mobil 1.

First off, most engines aren't super picky about grade, so they'll live happily on a pretty wide range of grades. The optimum balance of engine protection without being so thick as to waste power is what really determines the "best" grade. Thicker oil doesn't necessarily translate to "better protection" if the engine maintains enough oil pressure on thinner oil. In fact, thinner oils tend to get pumped more evenly throughout the engine, and circulate faster through the engine and thus provide a bit better cooling for the oil-cooled components (like the undersides of the pistons).

Secondly, 100k is NOT a lot of miles for a liquid-cooled v8. If its still got good compression, good balance of compression, low or no oil consumption, and good oil pressure, use the grade that is recommended by the manufacturer. I've got 4 different engines (1 Chrysler v6, three older Chrysler v8s), 3 with over 200,000 miles on the clock and 1 with

160,000, and I run Mobil-1 10w30 in all, which happens to be the recommended grade for them all. They all maintain good oil pressure at hot idle, and that's the point where oil pressure will fall too low if an engine's clearances have opened up too wide for the recommended grade.

I wouldn't run a Fram on a sewage pump, myself. Wix and Purolator make some of the better filters on the market. The Mobil 1 branded filter is also very good, although I think its a bit overpriced and I don't know if its available for that car.

Not much. ATF is far more stable and lives in a far more forgiving environment (no combustion by-products continually injected into it) than engine oil. IIRC, the 928 automatic uses good old Dexron-III just like Chrysler and GM did in the 80s. If you want a little extra insurance at more than twice the price, use Mobil-1 synthetic ATF. Otherwise, use a name-brand and follow the service schedule.

It's more than just a relabelled product. Whether or not it's a good idea for most car owners these days is debatable. They seem to have picked a market niche for the "regular" Mobil 1 and the "Extended Performance". The regular version comes in the 5W-30/

10W-30 weights that most manufacturers recommend these days, and 0W-40 which is supposedly for many European cars. There's also the 0W-30 which I believe GM recommends for cold climates. I saw the first three at a local Wal-Mart.

The "Extended Performance" version also seems to come in the 10W-40 and 15W-50 weights that a lot of DIY owners like to use. I saw the new "EP" Mobil 1, and the kicker is that none of them carry the API "Starburst" or "Energy Conserving" labels. They also only come with the API SL standard while the regular Mobil 1 now has the newer API SM.

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True. There are so many people who were convinced that 20W-50 had to protect better because it was thicker. The likely thing that might happen is a small power loss due to internal drag, and worse fuel economy.

The Mobil 1 filter is made by a contractor called Champion Labs. They make filters sold under any number of brand names. Some of them are OEM, house labels, etc. Many of their products are very good.

It would have been Dexron-II back then. I wouldn't recommend following some of the extremely high service intervals these days (i.e. never change the transmission fluid).

Of course I'm referring to Porsche's current list. When Porsche first started recommending Mobil 1, there were bulletins saying that they approved of all weights of Mobil 1 depending on ambient conditions or usage. It was probably not a great idea.

Of all these oils, only Mobil 1 0W-40 is the one I've seen on store shelves. A shop I've used does stock Kendall Synthetic 5W-40 though.

I thought ZDDP was considered and antiwear additive, and that "extreme pressure" usually referred to the (mostly sulfer compound) additives used in gear oil. IIRC, these EP additives aren't well suited in motor oil because they wouldn't survive the higher temps.

That's what I was guessing too. However - they seem to be targeting this series at the car well beyond its warranty period. The car well beyond its warranty period is probably not going to have a factory recommendation beyond API SL anyways. Not that this matters with Porsche, which comes up with a list of approved oils, and of which (regular) Mobil 1 0W-40 is on the list.

I looked, and I notice that they don't recommend any xW-30 or xW-20 oils... then I noticed the earlier page that referred to the Boxster engine ;-)

Air-coolers have different needs.... :-)

You're probably right on the extreme pressure terminology. I was specifically referring to sacrifical additives (of which ZDP is one) that are effective under high-pressure, direct metal-to-metal contact that exceeds the film strength of the base lubricant. I was using "extreme pressure" in the generic, not the specific.

Which is FINE with me- all the cars I care about keeping forever are WELL beyond their warranty period! New cars are boring :-p

This has come up on another thread on rec.autos.tech as well, and resulted in a link to some comments made by a GM engineer at:

If you plow through all the commentary and facts and replies (by the way, he believes any API-rated oil is just fine in the Northstar), you'll come to one point where he says that he wouldn't hesitate to run a Northstar right up to the built-in oil-life monitor's 12,500 mile limit, but would never do the same with an HT4100 because it has flat tappets, a gear-driven distributor, gear-type oil pump, and a non-roller timing chain, all of which eat up the ZDP additives in an oil much faster than all the other engine parts common to both engine designs (bearings, cylinder-to-piston friction, etc).

SO- if you ARE interested in taking the best possible care of an older engine that does have any of these features (mine all only share the flat tappets and distributor drive gear, because Chrysler v8s have always used gerotor oil pumps and I've got roller timing chains on them all), then an oil with a higher dose of ZDP is probably a very good thing to use, even if you don't run it to extremely high milage.

So i'll probably start using Mobil 1 Extended Life, but I'll still change it at around 7000 to 9000 miles, just like I've done for the last

15 years or so.

IIRC, it was exactly the same price at Schlep Boyz.