2003 blazer, low oil pressure intermittent

Hi all
My wife called me the other day and said her oil pressure dropped from around 40 to just below 20 after running errands took about 4 turns of the key to start the truck, she got home checked oil it was down a little but not much, topped off the oil and she went to work the next day same thing after driving on her way home all of a sudden the pressure dropped again, oil level was fine, any ideas?

Put in a quart of 20-50, and see if it maintains proper pressure. If not, try a second quart of 20-50. Be sure to draw off a quart each time.

If so, you might have too much wear in the crank and connecting rod journals. Change the oil, and go with half 20-50/half 30wt oil.

If it still drops, you are probably in need of a rebuild, short of using straight 20-50 oil (or gear oil).

There's always the possibility of a bad reading. Is the gauge mechanical, or electrical?

How many miles on the engine?
How many miles since the last oil change?
What weight oil have you been using?
Does the engine knock?

Don't trust the factory gauge, they are not known for their accuracy. Most auto parts stores rent oil pressure gauges: Check oil pressure on a fresh oil change when the engine is at operating temp at 2,000 RPM and at idle, then post the results.

Thicker oil will raise oil pressure, but at the same time, you lose volume. Using oil heavier than 5w30 will oil starve bearings, don't do it. There is a "cushion" of oil between the bearings and the journals. Thicker oil can not pass between the bearings and the journals as easily as thinner oil, as a result, the oil pressure increases trying to get between the bearing and the journal, as a result, the bearings don't receive enough oil.