[oil pan 4]

Biodiesel guys like test strips, but motor oil would turn the paper black.
A hand held pH meter that can do oily samples should work, just have to reset it to a known sample before every use.

Since all the additives I know about in oil appear to be alkaline and since we know acids are highly undesirable in the engine then I would think any reading less than 7 would mean its time for an oil change.

What insane specification does the fiat oil need to meet to make it so expensive?

On our VW it calls for some euro spec oil. I looked up the additive package on these oils and found out that the new generation of oils called for in the emissions controlled diesel trucks for the US market have additive packages very close to what VW calls for.
Turns out the VW oil spec for the late 90s and early 2000s is pretty close to what 2007.5 and newer diesel trucks call for.
The diesel truck oil is only $5 to $10 cheaper per oil change than the euro spec oil, not a huge deal but the real problem was no one had any around these parts. I can get this diesel truck oil from any local store. I had only been able to find the euro spec oil at stores in and around major cities no where near where I live.