as the title says, oil pressure reads fine while driving and declines at idle , reads zero after sitting at a long red at an intersection. responds , but slowly to revs in neutral. Anything to worry about ?

89 S5, recent rebuild

 

could be a faulty gauge or sensor, but you shouldn't bet your motor that it is because it really could be dropping to 0, which is not good, I assume 0 pressure would be terrible regardless of whether it's a fresh rebuild or not.

 

id like to know whats causing this too

 

YES & NO. I had an 86 that did this and never had any problems. I only had that car for a year or so.

Did it start to do this right after the rebuild? Where did the rebuild come from?

You could try cleaning the connection at the oil pressure sender unit. Or replace the unit. Try to borrow an oil pressure gauge to check the pressure.

 

^^ Sender/Gauge... probably sender....... if you truly had no oil pressure, you would know it before your gauge did.

 

what is fine when running? at least 30psi and closer to 60 psi is what is fine.

Sounds like a bad or mis-installed E-shaft thermo pellet to me.

 

I'm very suprised that NO ONE has suggested the o-ring in the front cover. This could be your problem?

Fine is about 30 at idle and 60 at 3k rpm. (oil mods change pressure and flow)

http://www.mazdatrix.com/faq/oring.htm

Good luck!

 

mine does that too. revs fine, goes to 60 when i'm on the gas but when it idles it drops to almost 0.

 

Go back and read that page you linked.

slipped or bad O ring loose pressure as the RPMs increase, it doesn't drop pressure as the engine slows.

 

SYMPTOMS of this problem are lower oil pressure at all times, but especially when the engine is hot. A slight "squeeze-out" can give 10-20 lbs at idle, 40-55 at 3500rpm, and drop to 35lbs at 5000rpm. A large "squeeze-out" can give almost zero at idle, and maybe 35-40lbs above 2000rpm.

Maybe you should read it!?

Notice how it says LOWER PRESSURE AT ALL TIMES!!!
I see how it can lower pressure as rpms increase, but after its sqeezed out, it will lose oil pressure at all rpms.

Now, why or how would a thermal pellet cause low oil pressure at Idle?

 

He said:
Fine while driving is 60 psi.

and again, he does not mention any drop as the RPM increases (a classic sign of a leaking or slipped O ring) Where as a bad thermo pellet will have about 15 psi low pressure all the time, and a bad install will result in almost 0 oil pressure at idle and around normal oil pressure above 2500 RPM.

And then toss in that it is about a 15 minute job to replace a bad thermopellet or use a bypass pellet, where as you are pulling the front of the motor apart for a O ring. Which would you want to check first? The 15 minute job, or the half a day job?

 

I got this too but haven't worried since its probably the gauge. S4 rebuild has street racing oil regulator though and 3 window bearings. I still got to check it mechanically, but it idles and runs perfect. Oh and one of the thermal pellet inserts.

 

I'm not near the car but the oil pressure rides about 3/4 up the guage which I think is near or above 60 psi . I drive it mostly between 4K and 6 k , even in the city ( 2nd and 3rd gear ). Drops down to about 30 psi at lower RPM, but just falls off to nothing during a long idle period. If i rev at the lights takes about 3 seconds to rise up to 30 psi , not instant rise as I remember it doing before

 

check it with a mechanicle gauge. Mine was reading low and when I checked it with the mechanicle, it showed i was runnung "decent" levels of pressure instead of worrisom (sp) levels. Its kind of tricky to get under there to do it but not all that bad.

 

Well, your both right:
This is a direct quote from the page: The pressure raises above idle until it gets to high rpms, when it lowers again. My car behaved exactly like the latter part or that quote. It had 0 PSI at idle, and about 30 when I raised the revs. When I tore the engine down, the idiot engine builder used the teflon spacer on an s4 casting, exactly as described in the link. Sure enough, it was smashed in one place and the o-ring was misplaced.

That said, it doesn't sound like this poster's problem, as mine behaved somewhat differently.

 

I have the a problem like that! i start the car, idle perfectly and smooth! oil pressure is at 30, let it idle for about 2 minutes, drop to 0, just give some gas, goes up to 30, rev it, goes up to 60 then come back to 30 and to 0. but can that problem cause failure to my cpu? cause it seems like i'm on a lip mod since i got that problem! i can drive the car around but cant go higher than 30 to 40 miles and my rps don't wanna go higher than 3.2. everything was fine 2 weeks ago, it started buy droping a 6.5 and now at 3.2. was able to go at 120 miles and as soon as it droped at 3.2 rpm, can't go higher than 40 miles. i don't know what else to do, i also checked my timing and it is perfect.

 

Mazdatrix archived their older web site and here is a link to a page referenced in an earlier reply. This post was in May 2021.

86-92 Front Cover "O"-Ring