(Overrides and/or supercedes all MY Driver Handbook recommendations)

Multigrade (mineral/synthetic) lubricants

10w-30 MY> 92 (synthetic)

5w-40 MY> 93,94,95 (synthetic)

10w-40 MY> 84,85,86,87 mineral or synthetic

10w-50 MY> 84,85,86,87 mineral or synthetic

15w-50 MY> 78>81,82,83,84 mineral or synthetic

20w-50 MY> 78>81,82,83,84,85,86,87 mineral or synthetic

Monograde (single viscosity grade) Heavy Duty (petrol/diesel rated) mineral lubricants

SAE20 MY> 78>81,82,83 and then from 89,90,91

SAE30 MY> 78>81,82,83 and then from 89,90,91

Note 1 - All MYs to 1988 - 20w-50 viscosity is not to be used below -15C

Note 2 - All MYs from 1988 - only use lubricants from the Porsche Approved List

Note 3 - From MY88 all lubricants are to have a petrol and diesel API rating

Note 4 - In MY81 the Oil Pump (OP) intake was modified to assist suction

Note 5 - MY82 as Note 3) above

Note 6 - MY83 as Note 3) above and OP drive was modified

Note 7 - MY85 the OP was increased in width from 21 to 23mm to improve hot idle oil pressure

SUMMARY

It can be clearly seen that the 928's Factory Approved lubricants were progessively modified from MY84 from 20w and 15w cold start ratings to 10w and 5w cold start ratings

The very good reason was better oil flow through the engine and especially the valve gear!

Note that the SAE40 (10w-40 and 5w-40) viscosity Approved lubricants commenced in MY84 and ran until the end of production - a period of over 10 years!

Recommending SAE50 (15w-50, 20w-50) lubricants was progressively stopped from MY84. From MY88 all lubricants had to be nominated on Porsche's Approved List

Note 1

There is NO evidence that any "excessive wear" has occurred at any time that required an increase in the lubricant viscosities. In fact it was actually the reverse as they progressively reduced the recommended viscosity both at cold start and at 100C points from MY84

This move would have been "tracked" via Warranty claims

Note 2

The modifications to the OP's intake(3 times) and the OP itself assisted in the reduction of viscosity specifications and helped to prevent excessive foaming, aeration and cavitation

Note 3

It is very clear that the Porsche engine development Engineers sought to use SAE40 (10w-40, 10w-50) multi grade lubricants from MY84. There is no doubt that a 5w-40 fully synthetic lubricant did all that they had found during their lubricant performance Tests during 1992. This was no doubt subsequently confirmed by end user and Warranty experience

This viscosity is still recommended retrospectively back to MY84 for all 928 engines along with only one SAE50 lubricant - Mobil1 5w-50!

Note 4

Nowhere was it ever officially suggested or mandated to increase the lubricant viscosity above those listed above to "fix a low oil pressure at hot idle" problem. Such a move is NOT one made by German Automotive Engineers in my experience. They will always fix the problem!

Confirming this I could not find a TSB that either suggested or mandated such a move!

Doug Hillary