Low idle oil pressure, worn pump?
 

I have been having what I think is low oil pressure on my S4 NA since I swapped it into my truck a year ago, I dont know if it is the famous front cover o-ring, a worn pump, or just nothing to worry about. I took some pictures on my way home tonight. I am running 10W40 Castrol GTX oil that is about due for a change, Mobil 1 oil filter, stock everything in the oil system except for the eccentric shaft thermal pellet replaced with an Atkins eliminator thing. I have the S4 oil cooler mounted as low as possible in the same orientation as the RX7 was. Ambient temperature outside is about -12ºC.

On a cold start, it takes about 3-5 seconds to build oil pressure, when the engine is warm, or when it is warm outside (above freezing), oil pressure builds within 2 seconds, when colder it takes another 5-7 seconds to reach full pressure once the gauge starts moving. I am using a mechanical oil pressure gauge, hooked up to the stock location, my oil temp gauge is reading from the oil pan in the stock location, and I have an aftermarket tach. I believe my oil cooler is draining back, causing the oil pressure to build slowly, but maybe its normal due to the long way from the pump to the engine. I also think the slow oil pressure build when cold is due to pushing the thick oil through the tiny tube that is about 8ft long lol.

My main issue is that at idle speed of 800RPM, when fully warmed up, my oil pressure is about 5-10psi, but it quickly increases, I am at over 40PSI by 1500RPM. The chassis that this engine came out of had 328,000KM, and was supposedly recently rebuilt, but I dont know what was done, possibly the original oil pump? Also, I noticed that my oil pressure gauge might start at 5psi? There are only 2 marks between 0 and 20PSI, where 20-40, 40-60 have 3, or 5 PSI per mark, so I dont know if the first mark on the gauge is 10PSI or 7PSI lol.

Anyway my pictures are attached, the pictures with the highest oil temp readings are when the coolant fan was cycling.

Sorry for the long novel, I like to make notes.

the spec is something like 71psi over 3000rpm with the engine warmed up. idle is usually around 30psi, give or take a bit.

if you're low on pressure, first thing would be the thermo pellet, as when its open, pressure drops about 20psi, and you should be able to see it open and close on the gauge.

next thing to check is the gauge, the stock senders get flaky

after that its likely to be the front cover o ring, which sucks

after that i've never seen as it doesn't really happen

-I have the thermo pellet delete already, is it possible to install it wrong? I noticed no difference in pressure installing this.
-If you see in the pictures, it is not in an RX7, using an aftermarket gauge, and it is a mechanical gauge also, with about 6-8ft of piping

I have a local ad on Kijiji selling an oil pump and drive chain, I figure if I can get it for $40 or so, I will take it, I have all the gaskets to replace the front cover O-ring, but I want to be prepared to replace the pump as well. I will be doing the repair with the engine in the truck.

I looked everywhere in the FSM, and I could not find a pressure reading, just the pressure relief settings.

The first thing to do is check the pressure with a diagnostic grade gauge, if it gives you the same readings, then look for the cause. I've worked on cars a long time, and I see bad gauges/senders a lot.

pressure relief setting is the oil pressure, sometimes the Japanese to Engrish transration is not clear very.

the oil pumps in the rotary do wear out, but even a totally shot pump will do the oil pressure spec

Based on your lower oil pressure on cold ambient temp start (when it should be very high with thick oil) versus hot start-

I think it is the front cover o-ring has been pushed out.

When oil pressure is super high out of the pump on a cold temp start it is pushing the front cover away from the oil pump outlet on the front iron before the oil relief valve in the front cover can bypass enough oil to drop pressure- and oil pressure drops.

When oil pressure is not quite so high on warm temp start the opening of the oil pressure relief valve in the front cover allows enough flow to lower the oil pressure so it isn't pushing the front cover away from the front iron.

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I ran the front cover with no gasket and with the race oil pressure regulator the front cover o-ring kept getting pushed out. Because I had no front cover gasket and I didn't take oil from the front cover (but front iron) the symptoms were never as bad as you are describing, but I noticed high rpm oil pressure would drop a bit when the o-ring was gone.

I finally put a dowel between the front housing and front cover so when the front cover gets pushed away the o-ring doesn't slip out. Worked like a champ.

Mazda really needed to put a front cover bolt right next to that oil passage to keep the front cover from flexing out.

i think with the FD and later castings they have an undrilled tension bolt hole in that area, might not be hard to do?

i also think that the older engines, with the front cover engine mounting, use the mounting to help keep the o ring in, the o ring pushes out on the FC's all the time, but it isn't so bad on the early cars

Very informative.

I happened to notice today after I was parked at the bank for 15 minutes that when I was sitting at the exit to leave, and at the set of lights 50ft away, my oil pressure was significantly higher at idle, they seemed to be in the normal range, and my oil temp was aroudn 160F, and my coolant temp was at normal operating temperature. First time I got over 3000RPM and came back to idle (next set of lights) I was back to my usual oil pressure. This happened a couple times today after I started the truck up from sitting a few minutes. Anybody hearing of a sticking oil pressure regulator? Wonder if my regulator is sticking partially open, and after the engine is turned off and oil pressure goes away, it pops back, until it has to pop open again and jams again. I picked up my spare core motor today and see that both regulators are easy to replace with the oil pan off, I may take them both off of this motor, clean them up, and try swapping them. My oil pan gasket is leaking anyway, and if it works, saves me a bunch of time.