Low oil pressure warning

[Tweddle]

1997 Eldorado, 83,000 miles. Well maintained, oil light on dash flicker. Digital display, stop engine. Tech changed oil pressure sender at oil filter location. check torque at crank. Replaced oil level sender in oil pan. Fresh synthetic blend oil change. 10/40. checked oil pressure with mechanical gauge, 30lbs cold, 15lbs after idling for 45 minutes. No oil flicker light on dash or digital display. After 2 hours of driving around town oil flicker returned on dash and stop engine display on digital dash. Odd no oil light was displayed during test, with sender removed and mechanical gauge installed. Anyone have any further suggestions?

[Cadillac Jim]

First, according to the 1997 FSM you should use 5W-30 or 10W-30, but never 10W-40.

Second, check the oil pressure again now and see what has changed.

One thing that can cause this problem is not enough torque on the front damper wheel. If the oil pressure is less now than when it was tested after driving just two hours, I would look at what was done with the car during the work.

A wrench, jack or lift can damage the oil sending unit. Look at the new sending unit and see if it shows damage, particularly if the oil pressure checks good.