IcemanG17

things to consider

1: the 928 engine was designed in the 70's and to use 20-50 oil, unless you are in near freezing weather
2: the 928 engine REQUIRES oil with a proper level of zinc....modern Mobil one does not have enough
3: how do you drive your 928? This is by far the most important ?? If you drive on the street with only the occasional blast.....almost anything of proper weight-zinc is fine.....if you drive on track (DE, track days) then the requirements go up.....

I have had great luck with both old mobile 1 and amsoil....I will run nothing but amsoil racing in my racers....."IF" I had a street 928....I'd get a street style oil....maybe the Z rod or something else....

Maleficio

My 82 really liked Redline 10W40. That is some fine oil.

Bill Ball

No kidding. This is totally incorrect. Mobil 1 15W/50 still has plenty of zinc (1300 PPM) and phosphorous (1200 PPM). It has not been reduced at all. It's all I have ever used in my 928, and I beat the living crap out of my car all the time and the engine still has perfect compression and less than 3% leakdown and produces the same power it always has while remaining untouched at 246K miles. I change the oil no more than once a year or every 12-15K miles, just as Porsche prescribes.

Brian, you ought to be ashamed of yourself for saying this.

http://www.mobiloil.com/USA-English/...duct_Guide.pdf

17prospective buyer

Wow, 15W50, any more viscose and we're getting into gear oil viscosity!! Does the 928 really need an oil THAT thick?

dprantl

+1 Bill. My car also has 246k miles and I also only use M1 15W-50 and only change once a year or 12k miles. I also do not drive it easily AT ALL. I don't understand why so many people bunch all Mobil 1 oils together when it is clear that 15W-50 still has the correct amount of ZDDP based on Mobil 1's documentation and also verified by independent tests.

Dan
'91 928GT S/C 475hp/460lb.ft

WallyP

Actually...

In order to help prevent early motorists from confusing gear oil and engine oil, SAE decided that they would add 40 to the actual viscosity number of the gear oil, so SAE 50 engine oil is the same viscosity as SAE 90 gear oil...

dprantl

A 75W90 gear oil is equivalent in viscosity to approx a 10W40 engine oil. So 15W-50 engine oil is technically more viscous than regular gear oil.

Dan
'91 928GT S/C 475hp/460lb.ft

Leon Speed

Says here for cars with cats Toco SEP is needed. http://www.torcousa.com/torco_product/sep.html

dr bob

It's 15 weight for cold flow purposes, with a hot film strength equivalent to a straight 50-weight motor oil. The common gear oils are equivalent to 25-, to maybe 50-weight motor oil viscosity at the highest end. There are some pretty serious turbine and industrial rotating-equipment lubricants that are a lot heavier, well beyond anything that our little mini gearbozes and differentials might even need.

I stock up on the M-1 when I see it, thinking that I don't want to be stranded if federal rulemaking decides that our 'old' cars really don't need oil after all.

17prospective buyer

What?? I never knew that. I suppose i should have. Isn't that more confusing? Why not keep the true viscosity rating to keep labelling consistent, then add a prefix like G for gear, or H for hypoid.

Bob; i understand the viscosity numbers, it's just that in the day and age where all i ever see is domestics produced by the millions that all use 5-20, 5-30, or 10-30, seeing a rating that high for a plain old V8 motor is just surprising to me.

Hilton

I never knew it either - fascinating stuff.

As for labelling - never underestimate the inability of people to actually know what they're buying, or to pay attention to what they're picking up off the shelf.

If Gear oil were labelled 30W50 and Engine oil were labelled 20W50, a VERY high percentage of people would buy the wrong oil for their engine/gearbox. The additives package will be very different between the oils.

Heck - I recently discovered my spare reverse light bulbs on the shelf at home are for 24V I obviously just assumed the stock there would be all 12V and didn't pay attention.

dr bob

Energy conservation and great manufacturing/design/engineering mean that modern engines expand and contract much more evenly and predictably. So clearances are more consistent, bearing materials might be better, and slipperier thin oils are the rage. Oh yeah, roller tappets are very common, cutting down tremendously on the high-pressure wear points that previously demanded thicker lubicating films. 5W- and even 0W- multiweights are common, and long-chain polymers make high film strengths possible in those seeming water-thin lubricants.


Back in the 'good old days', air-cooled engines often seemed to like thicker oils to help with the excessive clearances needed. Harleys regularly swallowed quarts of straight 60-weight non-detergent engine oil. Early 911's started life on straight 30 weight and proceeded up from there in the hands of uninformed owners. Choosing the right oil for an air- and oil-cooled car was always a compromise; Too thin and no hot oil pressure although there was adequate flow, and too thick meant that you'd have less cooling available from the oil. Until it got too hot, too thin, and no hot oil pressure. Solution: bigger 'racing' oil pumps. Or a water-cooled V-8 in the front instead of the air-cooled six back behind the windy area.