My 91 2.3ltr Mustang has 100K miles and has started sounding like a diesel engine (while running or idle). Also the oil pressure gauge is at the bottom (low end). The car has plenty of oil.
Any ideas on what it could be?
Oil pump. Probably already been run too much and the engine is damaged reading between the lines of your post.
That's a bad thing. Most likely a bad oil pump, but could be a scored bearing. As a temporary fix you could use a heavier oil, like 15W-50. But you're looking at a major overhaul/rebuild in the near future.
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