Well, I got a 92 civic d16a9 engine. I recently made an oil change, I've never done it since I bought it a year and a half ago, I know it's wrong but well the car was sitting most of the time, I only drove it like 800km on all this time so, not too much to worry about. I put a 10w40 because I live on Argentina and weather over here doesn't goes too cold (-5°c like too much) and it's get really warm at summer (+40°C) so by the chart that was the oil of choice, I put a Mobil super (over here Mobil ONE isn't that common to find) and a OEM oil filter, the thing is that now at cold start the oil light is remaining on a few sec and then goes off, and never goes on again. I suspect it can be the oil sending unit because I see it's leaking oil off a rubber cap on the exhaust camshaft right into it, I didn't check on the oil pressure sensor at the back of the block. In addition the other day I drove the car a couple of blocks at low speed and the engine temp on the dash wasn't moving when usually I drive a block or two and it starts to raise. Now, I'm planning to install a oil pressure gauge anyways.
Oil light never comes on again on operational temperature. I noticed that sometimes the oil light will get on late when switch to contact, or when engine been running, stop it wait two or three secs and then switch to contact (so there's isn't remaining oil pressure) im analyzing to clean the sending unit because oil was too old (it comes out brown but nothing else)

 

Here is how I have always checked oil pressure, If I start it, and it doesn't rattle, then I have enough oil pressure.
Done