So I checked my oil in my 89 GL,  it has a small leak and I haven't driven it in about 6 weeks it fired right up and had oil pressure. Put a little less than a quart of oil in and it had a little trouble starting... Turned over after about 15 seconds and runs great then I noticed I had no pressure it climbs as I rev it but dropped back to 0. I'm not a car mechanic but I know a sudden drop in pressure is not good, I'm sure it's something I did wrong but I've done oil changes on all of my cars and never seen this happen. Any info would be great.

EA81 or EA82? Auto or manual?

EA82 oil pressure gauges are notoriously unhelpful or inaccurate.  it’s probably fine and there’s no issue.

or reseal the pump  

What was the oil pressure doing before this episode?  It’s been consistently the same for 5 years?

Any recent engine work?

has the pump ever been resealed ?

It's a manual, 1.8 L wagon not sure if it's an ea81 or 82. The pressure was fine I'd say 20ish, I literally started it after it sat for 5 or 6 weeks it fired right up, checked the oil added about a quart went to start it again and it took about 15 seconds to fire up ( I bought the car about two and a half months ago and it's the first time it hasn't started right away) and saw that I had no oil pressure. I've done no engine work on it at all. not sure when the pump was last resealed. And like I said once it was running it runs great just seems weird that it happened right after I put the oil in. I put 5w30 in it, I live in Alaska maybe should have gone with 10w30 not sure.

Edited December 28, 20214 yr by Mj907
Added info

How long and how many miles have you owned this?

Is it a hatch back or wagon?

Its probably benign - EA82 oil pumps are notoriously inconsistent with pressure readings, ticking and the stock gauges aren’t great.

I would guess the timing is coincidence. Not surprising at all. Worth looking into but if it’s got oil in it snd running fine it’s probably fine. 
 

Many old conversations about low or zero EA82 oil pressure. Some owners manuals for the vehicle even mention low/no pressure reading at idle.

 

Edited December 28, 20214 yr by idosubaru

could the relief valve stick 'open' (far end of travel)

89 should be an EA82 SPFI engine, other option was MPFI turbo, but I'm not sure if they covered  that year.

At idle, it's normal for oil pressure to read near zero on the dash gauge.

I'm in CT, run synthetic 10W-40 year round.  I'm not sure what temp range you get, but 5W-30 might be a little thin. 

 

do your models with oil pressure gauge also have oil pressure warning light? I have seen someone say they won't work together, but I have that on EA82, and seen factory diagrams of both oil gauge and oil sender connected at different points on oil pump. My after market gauge sender failed, and I don't miss it scaring me saying low oil pressure. The oil pressure light will still light up just after an oil change, then go out. Oil light may be a late notifier of something amiss, but at least it still works

They originally have either gauge or light.  The same wire in the harness is used - slightly differently depending, but I have never seen one with both.  I converted my 93 from light to gauge when I got it, so I had to trace out all this wiring. 

So an update... Went back over after work today and it started right up and had oil pressure super happy about that, not many problems I have with cars just fix themselves! Going to do a full oil change tomorrow and go with 10w40 thanks for the responses everyone.

Sounds like there might be a fault in the wiring for the oil pressure gauge. Could be a loose joint/connection somewhere or possibly a dodgy sender unit too. 

A mechanical or quality electric aftermarket oil pressure gauge is a good back up to have, or just a good addition to the “too late” idiot light. 

Cheers 

Bennie

if it happens again .... when priming rebuilds, I do it from where the filter spins on. Not the centre hole, the other one, I shove clear pvc hose in it and a funnel. Pour oil down until it stops. It reduces chance of an air lock that I have had before.