Quote:
Originally Posted by Matt Monson
The Penngrade Classic oil is only GL4 rated. They don’t offer a mineral based Gl5 that I know if.
I’ve been putting my overseas customers in Motul HD 80w90 for a while now.
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Thank you Matt! I would not have figured this out without your suggestion here. Motul has so many choices and isn't very helpful when asked about which to use.
Just to confirm this looks like the stuff....
https://motul.co.nz/product/hd-80w90/
Also you were right about PennGrade. Their very helpful response here...
(hope they don't mind me posting this)
Dan,
Thank you for contacting D-A / Penn Grade / Penn Grade1 Lubricants and for your inquiry. Great to hear from our friends in New Zealand!
Let me start by indicating that the best source for any / all engine lubricant recommendation for your 915 LSD gear box is the OEM (Original Equipment Manufacturer). Best place to start is actual owner's manual....then perhaps a reputable service department / dealership. Please note that without the benefit of actual OEM information, my only source for lubricant recommendation(s) is various forms of in-house reference material (see below) and experience. If possible, please verify all of the aforementioned before taking action.
With that said......regarding OEM recommendation, my in-house reference suggests the following:
Porsche
1950-89
Manual Transaxle
911 (1986-77) – All: 90 GL-5
924, 944 80W, 80W-90 GL-5
928 75W-90 GL-5
Differential
924, 944 (1989-77) 90 GL-5
928 (1983-78) 90 GL-5
Now....I have researched competitor products that are often mentioned in Porsche threads. The one product often listed is the Swepco 201 Multi-Purpose Gear Lube......which I understand to be a GL-4 80W-90 non-synthetic gear oil. GL-4 and GL-5 are very different animals.......and yes, the Swepco product does contain limited slip. Our PennGrade 1® Limited Slip GL-5 Gear Oil SAE 80W-90 would NOT be a suitable replacement as it contains GL-5 level chemistry....not GL-4. The problem with using a GL-5 gear lubricant in systems calling for a GL-4 level of performance are the potentially damaging effects of the higher concentration of extreme pressure agents like sulfur and phosphorous found in GL-5 gear lubricants on yellow metal (brass, bronze, copper). GL-4 level is essentially ˝ the treat rate of GL-5 level. So.....a GL-5 gear lubricant would NOT recommended for use in GL-4 applications......conversely, GL-4 would NOT be recommended in systems requiring GL-5 (not enough EP).
We have a terrific, conventional based GL-4 gear oil (PennGrade1 ‘Classic’ GL-4 80W-90), but it does NOT contain limited slip that your 915 LSD gear box likely requires.
Please feel free to contact me should you need further assistance. In the interim, please confirm actual lubricant recommendation for 915 LSD gear box before acting