Guys

My stock oil pressure gauge recently fell to zero and registers no movement at all under any conditions (at idle, WOT or anything in between).

Oil level is stable and there are no leaks.

I know the pressure sending unit is prone to failure and I’m trying to determine if that is the problem.

I’ve verified the stock pressure gauge is ok (grounded the electrical connector, turned on the ignition and the gauge moved to maximum).

I’ve just tried a crude test to determine if oil pressure is present in the engine.

I removed the oil filter and started the engine expecting that oil would squirt out under high pressure (60 psi or so).

It didn’t. The was plenty volume of oil coming through the inlet hole where the filter sits, but it wasn’t what I would call under pressure.

I put my finger over the hole and felt no resistance at all, certainly not what you’d feel if you stuck your finger over a garden hose for example.

Has anyone else tried this crude test and if so, what did you see?

Many thanks

 

I tried it too sometime, only on the pressure hose going to the turbo. I also found no oil coming out. My defi gauge however senses oil pressure......

 

Thanks skim41. After seeing no oil at the pipe, what pressure reading did you get from your gauge with the pipe re-connected? Also, is your gauge mechanical or electrical, is it connected to the standard stock place on the rear housing?

 

its rare to have an oil pressurizing system just fail (without a major leak)...The chain would have to break...the sending unit however can let go at any point.

how many miles on the engine?
when the last time you changed your oil? (does it smell like fuel?)

my opinion is the stock gauge isn't accurate under 30psi (which should be around where it reads idling)

that crude test you described is a method used to know when a fresh engine is primed. My stock gauge (95) never registers oil pressure until the car fires up (my friends 93 registers while cranking)...so, I didn't know if my motor (first build) was making oil pressure until it seeped from the oil filter pedestal (I just unscewed the filter a little)

 

Was running the engine in following a rebuild (by me), had covered 980 careful miles when the pressure gauge reading died. The oil and filter were changed 500 miles ago

 

so you actually ran the car with the filter removed...not just cranking??

your first 980 miles, what rpm would you reach, and what was the oil pres readings?

New bearings in the build?

what were you doing when the gauge dropped? all of a sudden? or luggish than dead??

did you use a new teflon insert and o-ring under the front cover?

 

Yes, started the engine and let it idle for a few seconds with the filter removed. Then shut it down when I saw that oil was emerging from the inlet hole on the filter pedestal.

Never went above 3k rpm during the 980 miles and the oil pressure gauge would typically read between 1/4 and 1/2 way up. Always went around 3/4 way up from a cold start then slowly dropped as the engine warmed up.

Yes, all new bearings in the build with clearances cjecked and within spec.

I was cruising at around 65mph (around 2.5k rpm) when the gauge slowly dropped down to zero. Slowed down and "feathered" the throttle a couple of times to see if the needle would move (it didn't). Drove it home real easy (couple of miles). Engine starts fine and runs smoothly.

Didn't use a front cover gasket, used Versachem Grey 999. Discarded the teflon insert and used the appropriate sized o-ring which came with the Rotary Aviation kit.

 

Its the sending unit.

 

yep.

 

Saxyman990 spun a front bearing using an oring...

https://www.rx7club.com/showpost.php...8&postcount=20

not trying to scare you, but it can happen.

 

Too late, you already scared me...
The replacement o-ring is thinner in cross section than the stock one (to account for the difference in height when not using the front cover gasket), it sits only slightly proud in the machined counterbore so shouldn't go anywhere (have used this before on a previous rebuild for coolant seal failure).

Regarding the sender unit, there's a guy at work who reckons we could use a controlled supply of compressed air to apply pressure and test the electrical output with a multimeter. Will give it a go on Monday (before I commit to buying a new unit)

 

check the wiring too...its a single wire connector and it can get caked with road grime and what not and corrode or break.