I just did: I got none.
Had a porous casting back in '91 on a transmission in a brand new Grand Marquis. Usually does not take years to manifest itself. Most now do a process called “Hipping” to decrease the incidence of porous castings. A process that subjects the casting to high pressures during manufacture. We do this for some of our castings that are prone to porosity and need to contain very thin dielectric oils…
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I just googled it here, and this was the first of several hits
“The rear diff housing is slightly porous on my S3 & is dripping a nice puddle.”
I googled it last night when you first posted, ‘ol bean. I got the same British conversation. Bollocks!
Several different conversations that seemed to be British folk as a matter of fact. I found that odd, mate. Must be more common in England. God save the queen, and all.
I think folks in England are more into old cars than here in the USA. why? don’t know.
And land rovers. Probably lots of porous stuff on an old Rover.
You will have more luck googling “porous casting”.
Here’s some images we had done recently to look at casting defects. High magnification, SEM, XRay type images. Maybe you find them interesting:
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You Googled porous axle casing , not “porous axle casing”; Googling the latter turned up only this thread; Googling the former returned 218,000 hits.
Wouldn’t a casting defect have shown up before 32 years had passed?
I finally got my 24mm socket and the fill plug off today. Oil came out. I checked the level of the bed both above and beneath (I have a level with a magnet): it reads level. I released the emergency brake and put it in neutral: I can’t get it to keep rolling in either direction. It seems level.
Of course there’s a suspension between the differential and the chassis so chassis-level may not imply diff-level. How can I check the diff’s level?
The differential is full, now you can move on to something else.
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Why was there gear oil on my differential?
They tend to seep when they get old, I don’t think that I have a spotless differential under any of my vehicles.