The following note was co-authored by Albert Broadfoot - my thanks to him!
Note that the 924S, 944, and 944S have an oil/water heat exchanger, while the 944 Turbo and 944S2 have instead an oil filter console that routes oil to an external radiator. This procedure applies to all 944-series cars as well as the 924S.
Identify the type of oil pressure relief valve on your car. There are four versions of the valve that Porsche has used. Two are obsoleted by two newer versions, so there are in fact only two versions that you need to be aware of.
model year model(s) qualifier version 1982-86 924S, 944, 944 Turbo all A 1987 924S up to engine no.
43 H 01919 - manual
43 H 60384 - automatic
A 1987 924S from engine no.
43 H 01920 - manual
43 H 60385 - automatic
B 1987 944, 944S, 944 Turbo- all B 1988-forward 924S, 944, 944S, 944 Turbo, 944S2 all B
In original production from 1982 - 86, a three-piece spring and piston oil pressure relief valve was used. In 1987, a one-piece version was introduced as a retrofit to early production cars. There does not seem to be any service bulletin which suggest the retrofit is recommended except where the original relief valve is not operating properly.
The following part numbers are relevant to servicing early production cars:
part number valve 944.107.035.11 o-ring 944.107.935.11 seal ring N.043.815.3 alignment tool 9215 000.721.921.50
Porsche began producing model year 1987 engines in July '86. These engines received a new type of one-piece oil pressure relief valve. Unfortunately, in engines produced between July and October, the relief valve was not anit-corrosion treated. Porsche recommends that when servicing these engines, the oil pressure relief valve be replaced with the corrected, anti-corrosion treated part.
The affected engines are as follows. The second column has the first engine numbers in production that received the Version B, untreated valve. The third column indicates the first engines that received the corrected, treated valves.
model engine number,
924S/944 manual 43 H 01920 43 H 05373 924S/944 automatic 43 H 60385 43 H 61268 944S 42 H 00140 42 H 02847 944 Turbo 45 H 00086 45 H 01256
The following part numbers are relevant to servicing Version B relief valves:
part number valve 944.107.035.01 o-ring 944.107.935.01 seal ring N.043.815.3 alignment tool 9262/1 000.721.926.21
You'll need a 24 mm. open crowfoot socket to perform this procedure.
You'll also need the correct alignment tool described above. Some folks just use the oil pressure relief valve itself to do the alignment, but we recommend using the proper tool for better accuracy.
You'll need a kit with new style seals and a gasket for the housing ("console"). It costs roughly US$20.
The job takes about 45 to 90 minutes, once you have the car safely jacked.