Apologies for making a thread but I was searching through a plethora of oil pressure threads on the site last night and did not manage to find the answer I am looking for.

I was at a track day yesterday and enjoyed hooning my car all over the circuit but I noticed something about my WOT oil pressure that has me wondering if it is normal.

To start, I run 10w-40 Shell Helix HX7 semi-synthetic oil and always have with the FD and my RX-8. I have a '99 spec car which means I don't have a stock oil pressure gauge. However, I have installed a Defi oil pressure gauge in my car and the Defi oil pressure sender is installed in the factory location where the early spec cars have their OEM gauge plumbed into.

It looks kind of like this:



At idle, my oil pressure when warm is about 160-200 kPa = 1.6-2.0 bar = 23-29 PSI

Under normal driving and cruising conditions oil pressure steadily increases to about 700 kPa = 7 bar = 101.5 PSI around 3,000-3,500 RPMs, whereby it remains flat at any RPM above that threshold.

All seems fine to me but I noticed when going WOT on the track my oil pressure was pegged at about 600-620 kPa = 6.0-6.2 bar = 87-90 PSI all the way to redline.

Why would the oil pressure be reading lower under full boost and WOT compared to when driving normally?

Is that normal or do I have an issue?

I experienced no problems on the track and my catch can remained dry (thank you IR Performance for the baffled filler neck! It's helped a lot!).

 

Higher oil temp on track => lower oil viscosity => lower oil pressure

 

Your pressure numbers are fine but I would step up the oil weight on the track to a 20w50.

 

Oil temps were never over 90 C (195 F) as it was a very cold 8-9 C (45-50 F) day in England and I have the factory twin oil coolers. Would it start thinning out at these types of temps?

My original thought about 20w50 was that England's climate is too cold and that oil is too thick? Plus, having a 99 spec car I have the revised oil injectors (and OMP) which have a much smaller orifice. There is a theory that the reason Mazda started recommending 5w30 on 99 specs over 10w30/40 was the change in the injector size. I could be spouting a bunch of BS for all I know and this is just what I read on the Australian forum although the 5W30 recommendation is in the Mazda Japan manual that came with my car when it was originally purchased from a dealership in Japan back in 1999.

If there is any real world experience running the thicker oil with the smaller injectors with no issues then I may give it a go. I was also running about 400-450ml of premix on the tank of gas, making for a nice sweet smell from the exhaust and a bit of smoke while idling cold :-)

 

Of course it gets thinner with increased temperature, from ambient on up (and thicker with lower temps, natch). Perfectly normal, it's not like it's failing you. 90psi seems like *plenty*, maybe even a bit on the high side.

Going to a higher viscosity will reduce oil flow, btw. I think you're probably fine where you are, might even consider 10W30...

 

Thank you ZDan for the assurance. Is 90 PSI really on the high side? What have other people experienced under track conditions?