89 300e low oil pressure....
 

Recently did an oil change. About 3 weeks later, I noticed my oil pressure gauge reading low.. About .1 bar at idle, 1 bar while driving.

I thought I must have installed a bad oil filter..

I did an engine flush, switched to synthetic, new oil filter..

Now Im up to .75bar at idle, 2 bar driving.

Classic oil pressure sending unit symptoms.....

Changed it out yesterday with no change.. I am getting good oil pressure all the way to the top of my engine. I can physically see the oil squirting out of the oiler. More throttle = more oil..

I doubt I have a mechanical issue, but I dont know what to check next.

Any advice?

Unless you have a pressure tester, there's not much you can do. Low oil pressure either means a blockage at the point where it picks up the oil, a bad oil pump, a bad sending unit, or increased clearance in the crankshaft (and other) bearing journals.

Or, simply a bad gauge...

FYI - an engine flush can be a bad thing, especially if you don't do them routinely. They have a tendancy to dislodge large chunks of nastiness and deposit them all around your engine's oiling system, sometimes blocking up things that ought not be blocked up.

Try removing your sender and checking to make sure enough oil is getting to it to read the correct pressure.