This is bad news, don't drive the car until you get it fixed. If this was a sudden change then your in luck, if not you need another engine or a rebuild. It is definitly thermal related and I seriously doubt it is all bearing wear. On a cold start the pressure gauge should be pegged.

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green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

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