Earlier today I was sitting at a stop light and noticed that the oil pressure (according to the stock gauge) was sitting on zero. I revved the engine up to about 2-3k and it went up to about 40-45. When it let it idle again, it went back down to near zero. Any idea what could cause this?

 

check you pressure sensor connection and you oil level and make sure your car is at normal idle speed

 

Mine does this too... i think its just a crappy guage

 

I just added some oil a few days ago, so the oil level is fine. I have a large street port, so my idle is kinda rough. When its steady, its usuallu around 800-900, but when it gets below that it gets a bit of the brap-brap going. It usually goes from about 650 to 1000 once its been idleing for a while. I think this is normal for my car since its been doing this since it was rebuilt (its got about 8k on it now). The air adjust screw doesn't change the idle a whole lot, though, so I'm wondering if something else is wrong. Anyway, I dont think it was doing this before so I doubt the idle has much to do with it. Also, would the sensor being loose cause the reading to go very low at idle, but relatively normal other times?

 

+- 200 or so rpm at idle isn't going to change your oil pressure. You might have a bad pressure sender or thermal pellet. You could try:
Clean the connectors and /or check the pressure sender
or rev the engine to 3000 rpm and see where the oil pressure is. It should read near the 60 mark on the stock gauge. This is where a "real" gauge comes in handy. If all is OK, the sender could be just dirty or bad.

 

As with any electrical connection, you need to have a tight and clean connection. If that connection is loose, you have found the problem.

 

yeah, it sounds like something is more wrong with the gauge/wiring than the oil in the engine.

 

You can check the gauge and wire harness at the same time, by groundig the cable. If it moves, then the gauge is working, since you can see the gauge working when the engine is running, I will say the sender went south.

It is a common issue on our dated vehicles, on the Miatas too)

 

Bad bearing?

 

Sounds just like my problem, it was the thermal pellet.
Simple fix, now 20PSI at idle, 60+ PSI at 2500 RPM.

 

Ok, looks like I've got a few things to check for. If the sender is bad, do you think getting one off a car in a junk yard would be ok? Theres an FC less than 10 minutes from my new apartment. Someone has already taken everything that could possibly be used from the interior, but he hasn't taken much from the engine.

 

Errr... have you even considered that you might be using the incorrect oil viscosity for your climate?

 

Give it a try, on my case I used one from a Jspec engine, and that one was even WORST.

 

You an use the thiniest oil available on any automotice chain store, and still wouldn't read zero at idle (assuming everything else is in good working condition).

 

I use Castrol GTX 20W-50, so its not too thin. What is the pressure supposed to be at idle, anyway?

 

i have the excact same thing happening with my oil pressure guage.

It has been like this since my last rebuild.
i have not had any overheating issues and i also have a mild streetport with 3mm seals from Rotary Power in Gardena

 

Shouldn't you check if you're 100% positive it's sender or gauge?
Everyone should at least have an aftermarket oil pressure and water temp gauge. I'd be sweating my *** off if the gauge shows "0" or near it on a fresh rebuild. You should get it fixed.

 

TEST
Per man FAQs and rebuild procedures, 1. Remove the stock oil pressure gauge unit.
2. Install a test/reference oil pressure gauge/meter (US$40, ask the local retail automotive shop)
3. Start engine, warm to operating test (could drive to warm before installing test meter, but avoid burning yourself)
4. Run engine to maintain 3k rpm, gauge should indicate approx. between 441 and 539 kPa (4.5 to 5.5 kg/cm^2, 64 to 78 psi)
(shutdown and replace)

I understand another rare cause of low pressure is the pressure bypass that returns overpressure flow to the oil pan can jam with gunk, so it opens to regulate to bypass excess high pressure oil and can bind against large debris contaminants such as a metal bur or filter fiber. Some might agree -- not bloody likely.