Hi

I always had low pressure according to the oem gauge but didn't pay attention since it's famous for displaying unreliable values (sometime the needle jumps, etc..)
But I installed a new aftermarket oil pressure gauge 2 weeks ago, and I'm really concerned about my oil pressure being quite low at idle. When warm, it's sitting at 1b/14psi when I believe I should expect 30psi.
When driving, the pressure increases progressively and looks almost fine from what I've read :
3b/45psi @3k rpm, 4b/60psi @4k rpm and so on until 7b/100psi around 7k rpm.

I spent some time searching for reasons and stumbled upon 3 potential causes :

-The oil pressure control valve. I never heard about it before, but from what I've read, the spring may break or wear, and maybe explain this low oil pressure?

-A piece of silicone gasket that detached inside the oil pan and obstruct the Oil strainer ?

-The thermal pellet. I believe it shouldn't be the case for me, because I've had a rebuild last year/2000 miles ago and I'm using the Atkins thermal pellet (always open, doesn't fail)... unless it hasn't been mounted on correctly...

For information, my aftermarket pressure sensor (prosport) is installed on a sandwich plate under the oil filter. The car runs like a charm, the motor doesn't leak, I never had to refill oil in +1000 miles, the oil level keeps really steady.
I'm using the mazda oem oil filter, and 10w40 semi synthetic oil. I was using 10w30 mineral before I notice this problem, the 30>40 grade helped slightly, but not enough. I'll try to avoid 20w50 since I'm in a not so hot country (North of France).

Please let me know what you think.

 

Oil pressure problems are uncommon but they are tricky to solve if they do crop up.

I would think you either have an internal leak - like the o-ring between the engine and front cover is bad/deformed and is leaking pressure back to the oil pan, or something went through the oil pump and it's sloppy and not as efficient. The RTV on the oil pickup is a maybe but I think you would see problems at higher RPM moreso than lower RPM.

Also you really should be seeing about 60psi at 3000 rpm. That's usually my rule of thumb - 30psi at idle, 60 at 3000 RPM.

Is the motor original to the car or was it rebuilt?

Dale

 

Fuel dilution will also cause low indicated pressure.

I think the FSM says 50 psi at 3000 rpm. Not sure about the resolution of your pro-sport gauge but you’re not that far off from that.

 

Thanks for your advices.
Dale, the engine is the original from my 7, 110k km, and has been rebuilt last year. It's currently finishing breaking in, approx. 2000 miles since rebuild.

Oil dilution, damn I didn't even know about this phenomenon, but it looks pretty bad from what I've read. I don't know if it could be my case, but when smelling my last oil change (which had approx. 600 miles on it) it smelled a bit gasoline... I thought it was something normal for a rotary, but I really don't know if it's usual or not ?

 

If the oil pressure is fine immediately after an oil change but degrades as time goes on, that could be dilution. When was the last time you changed oil?

Who did the rebuild? There's a number of things that can be messed up on a rebuild that can cause low oil pressure. Of course you may not know what the pressure truly was beforehand.

Dale

 

Yes, that's exactly what I was thinking about oil dilution, and so I think I'm safe about this. Cause I changed the oil 2 said ago and the problem was the same right after the first engine start. (Well, after the engine was warm after the first start)

Indeed, I don't know how was the oil pressure beforehand, because I've put the car to the garage as soon as I bought the car.
The rebuild has been done by a professional. He's almost the 'only one' reputed in France at the moment, he has experience with FB/FC, but my fd was his first one. And since he messed up many things (wrong hoses connections, mismatch WG/turbo precontrol plugs, forgot to plug back one valve's hose...) I'm really starting to think he could have fucked up inside the engine too...

 

Well, the more I think about it, the more I find the internal leak or the lazy oil pump the most probable causes. Thanks Dale again for helping pointing me out the targets. I'm gonna check how difficult it is to open and check the front cover to have a look inside... I already know opening the pan is a hassle 😆

 

The front cover is possible to pull with the engine in the car, but you won't want to do it. You're way better off pulling the motor and doing it out of the car. You will also have to drop and re-seal the oil pan as well.

I did some front cover jobs on FC's back in the day and that is hands down the LEAST fun thing to do. You're way ahead of the game to pull the motor.

There's an oil passage between the front cover and the block that seals with an O-ring and a Teflon spacer. When you pull the front cover pay special attention here, if something is wrong there that will result in lower than normal oil pressure. Forgotten Teflon spacer, pinched O-ring, etc. There is a metal front cover gasket available that does away with all that - you just install the gasket and you're good, no O-ring needed.

Dale

 

Prosport is not a good gauge brand and the stock sender is notoriously flakey. I would confirm with a quality mechanical gauge reading before tearing anything apart.

 

^This. In addition to the gauge probably being a little inaccurate, it’s not unusual for me to see indicated pressure a little low or fluctuating at idle. I believe the signal is weakest at idle and it has a little trouble getting thru the connection. Mine has been like that since I bought the car 85,000 miles ago and it’s aggravated a bit by a little fuel dilution (which is common in these engines) as I near the time for an oil change. Your pressure increases with engine speed and is about where it should be at 3k rpm. I really think it’s premature to consider an internal problem.

 

Thanks Dale for those infos, very useful to me.

Well, I'm still having some hope that it's not sooo bad. I've ordered a new oem pressure sender. And I'll probably check with another aftermarket gauge. And only after this, I'll find out what 's next...

I'm definitely not happy with those prosport gauges. The afr one displays random values since I installed it, and even if I bought it new, the brand refuses to change it...
I choosed this brand because they look like oem (needles white, orange with lights) but I think Iwill remove them all.

 

Trying to stay on topic here, while simultaneously voicing my question. I was under the impression Prosport gauges are good quality gauges? I mean, when I originally came across them back in 2007 I remember their boost gauge to be pretty accurate when I compared it. Though that is a huge timeframe gap for quality to change.

 

Sounds similar to problem I had with my Turbo FC when I increased oil pressure over stock (80psi stock on those?) and it would push the front cover away from the front side housing allowing the oil passage o-ring between them to come out.

I dont know if FDs which run high oil pressure stock have the same front cover o-ring issues or not.

Never heard anything good about Autometer gauges. I have the old Autometer boost gauge from the 90s in my FD. Its not very accurate, but "good enough" to get a general idea whether things are operating in the normal range. Good luck seeing it at night though- poorly lit.

 

The 86-88 FC's had an O-ring between the front cover and front iron that was only supported by the (paper) front cover gasket. I could see running higher oil pressure could deform that seal and cause problems.

89 they changed to a similar setup to the FD, there's a larger diameter space for that passage so you use the O-ring with a teflon spacer/reinforcement around it and then the gasket. Thinking about it the teflon spacer is probably to back up the O-ring and keep it from blowing out.

At some point in time Mazda made a metal gasket, it's similar in design to the turbo oil drain and the upper intake manifold gasket - steel with a raised lip that compresses. With that gasket you don't need the O-ring, it does all the sealing and does a great job of it. I think that gasket may have originally been for the Cosmo 13b or something, or maybe a revision of the FD engine (like in 96 or 99) Regardless Atkins Rotary has them.

Dale

 

My issue was with S5 ('89+) side housings. I finally dowelled the o-ring land so it couldnt go anywhere.

 

Final update :

I've been able to replace the oem oil pressure sensor by a new mazda one. (Thanks atkins)
And, fortunately, I've got the good oil pressure now !
30 at idle, 60 under small load
Problem solved !

 

Whew! Nothing like getting a scare from an aftermarket gauge!

Dale