my oil pressure's been acting up lately. It's fine when I first start it in the morning or when its cold, oil pressure shoots up immediately. However when I start it again after I've parked it for a while ( 3 or 4 hours ) , oil pressure takes a few moments to build up, do you guys experience this as well?
Here's a video to show you what I mean

 

When oil is at room temperature(your car after sitting 12+ hours in 70F weather), it is the viscosity of oil at room temperature. I say that because I want you to picture how oil flows and how thick it looks when you are pouring it out of a new container into your engine.

Now, at operating temp, which the industry standard for oil is 212F, that same oil has a viscosity much more similar to water.

So, which do you think will flow more easily and with less resistance, keeping in mind that pressure is created not by the oil pump, but by the amount of resistance that the oil it's pumping sees?

Cliffs version:
Room temp oil= thick oil which= more resistance which=more pressure on your gauge until the oil heats up.

Warm oil(your car after sitting in 70F weather for 3 hours)=thin oil which=less resistance which= less pressure on your gauge.

Everything looks fine to me. Normal warm idling pressure on a stock B18 just for example will be 10-15psi, where as cold startup idle pressure will be more like 60psi.

 

That's about right