Vw 8v low oil pressure?

This is about my sisters 1992 jetta.

It was purchased with ~90k miles, and the seller was nice enough to warm it up before we looked at it so it ran great, but on a cold start it would clatter loudly for 3 seconds or so and make a huge cloud of blue smoke. I found a rebuilt head for cheap and replaced the head, and when I took the old one off the valve guides were so worn the valves would rattle around when you moved them. This also decreased the oil consumption from one quart per tank to maybe one every 4 or 5 tanks. It didn't change the rattling on cold start though, although it sometimes doesn't do it. Other than that it has ran fine for a couple years. Recently in the hot weather when driving the oil pressure light has started coming on, and according to what my sister says it's been doing it more often now. Would the oil pump fail in a way that would cause this? Or is it more likely the engine is just worn out with less than 150k miles? Since buying it it has always had regular oil changes with good oil and filters and not been run low as far as I know, before that I have no idea.

What weight oil and what filter is being used?

Mann oil filter and lubromoly 10w-40 until the last oil change which was 15w-40 of the same brand.

Seems like you have the right oil filter and oil. 20w-50 could help bump the pressure up a bit.

Did the rebuilt head come with new lifters?

I think an oil pressure test is a good start to find if it's a pressure problem or just worn lifters.

I'm more concerned about the light coming on more and more in the last month than the lifter noise, but I do want to test the oil pressure. I think the lifters were lightly used, it did pretty much the same thing before I swapped the head too.

It isnt that unusual for an 8v oil pump to do that. Put a gauge on it and confirm you dont have a sensor problem and throw a pump on it.

I seem to remember something about oil pressure switch updates for 8v engines... But I can't remember if it was for A2s or A3s... But you should still check what the actual oil pressure is with a manual gauge... At both points, head and oil filter housing. At least that will tell you if there is a pressure problem or switch problem...

With no or low pressure are you getting lifter noise?

Don't they kind of go together ?

Yeah, that's semi-common with the 8v. Just put a new pump in and be done with it.

+1 on the oil gauge test( in the areas that noddaz said)

It doesnt sound that unusual when its warm, sometimes its way louder than my mercedes diesel when its cold though.

those high & low sensors go bad all the time, id replace them and see if the buzzer keeps coming on.