Bumped into the prior owner, she told me where they had gotten it serviced, so she thought. I also called all the places listed on CarFax
Seems car never had an oil change in her hands after I called those places. At least 35 k miles but as much as 50 k miles ...
I have a back up engine identified if I need it,
Here's what i did after oil pressure light came on and I discovered the sludge
1. Change with Mobil 1 ESP and Mobil filter drove 250 miles, (still had light after starting for a bit until getting warm)
2. New oil and filter change. Still had light after starting for a bit until getting warm. (oil was black but not thick and no sludge pieces or gum evident in the oil of filter
3. Drove 100 miles, light came on as before (again when cold, gone after warming a bit more)
4. Added 2 oz MMO drove 50 miles. Still light came on when starting, Did not go out until very warmed up (10-15 minutes at full temp.)
5. Added more 2 oz MMO, drove 50 miles same as 3 above.
6. Added 2 more oz of MMO drove 250 miles. pulled the filter, looked good, dark amber color no sludge evident. Changed oil pressure sensor.
Light did not come on again. YAY , so far. Thinking it got clogged with sludge and these are an issue on these cars regardless
7. Drove 50 miles. Added 10 more oz of MMO 16 oz so far. No pressure light.
8. Drove 250 more miles. No light, oil on dipstick is a little darker but still had nice consistency, no sludge to be seen.
Next steps:
9. Will drive another 250 and pull the filter (500 miles with 16 oz of MMO) and if it still looks clean, will add the remaining 16 oz MMO (1 qt MMO : 5 M1 ESP)
10 If Car still seems fine no oil light, I will drive 750 more on the 1:5 MMO/oil mix (2000 total) pull the filter again.
11. If all looks good I will drive another 1000 k and change to all M1 ESP (after 3000 miles total with various concentrations of MMO (2000 miles on 1:5 mix)
12. I will check the filter after 1500 miles on the full oil change. Will send out a sample for UOA
Hopefully I will not see continued metal or other deterioration in the analysis. If so, that's another thread.