6 replies to this topic

[dtfastbear]

Hey gang,

Pretty fundamental question, but I didn't find any answers through searching...

What's the normal and acceptable range for oil pressure in a spec miata engine under race conditions? On past engines, my data has shown it to be in the high 40's to mid 50's under load. We melted down an engine recently, and I put in a spare. It's showing the OP fluctuating in the low 30's under race conditions.

I'm running Redline 5-30 oil if that makes a difference.

Is that too low?

Any advice is appreciated.

Cheers,

Dean

[Duncan]

Hey gang,

Pretty fundamental question, but I didn't find any answers through searching...

What's the normal and acceptable range for oil pressure in a spec miata engine under race conditions? On past engines, my data has shown it to be in the high 40's to mid 50's under load. We melted down an engine recently, and I put in a spare. It's showing the OP fluctuating in the low 30's under race conditions.

Is that too low?

Any advice is appreciated.

Cheers,

Dean

That sounds pretty low. My max oil pressure (99) is around 55psi under race conditions.

Duncan

[James York]

That sounds low. My Kinetic-Sunbelt was always over 50 at WOT/high rpm race conditions. I use 0w-30 race oil.

[dtfastbear]

Eh, I'm sure it's just the gauge, right?? ;-)

I'm going to try a new filter and running 10-30 and see if it makes a difference. If it stays this low, I probably will tear it down.

Cheers,

Dean

[Duncan]

Eh, I'm sure it's just the gauge, right?? ;-)

I'm going to try a new filter and running 10-30 and see if it makes a difference. If it stays this low, I probably will tear it down.

Cheers,

Dean

When you drain the oil, capture some in a clear container. You're looking for shiny little flecks (bearing material. I would also cut the filter open and check that as well. Fingers crossed.

Duncan

[Duncan]

Also, FYI, since the oil pump is a positive displacement pump with an internal bypass, the load doesn't really affect pressure. Output pressure of the pump is simply a function of how fast it's spinning. Once it spins fast enough to open the bypass, it will hold that pressure all the way to max-rpm.

Oil pressure as measured by the gauge is a function of engine RPM and oil temperature/viscosity due to location of the sending unit. For example: colder oil will produce higher pressure at a given RPM due to the higher viscosity.

Bottom Line is that when you're checking to see if your oil pressure is consistent event to event, you should only check data points at high rpm (after the bypass is open) and when the oil is warm. Your pressure should be essentially constant during this window.

Duncan

[Tom Sager]

Also, FYI, since the oil pump is a positive displacement pump with an internal bypass, the load doesn't really affect pressure. Output pressure of the pump is simply a function of how fast it's spinning. Once it spins fast enough to open the bypass, it will hold that pressure all the way to max-rpm.

Oil pressure as measured by the gauge is a function of engine RPM and oil temperature/viscosity due to location of the sending unit. For example: colder oil will produce higher pressure at a given RPM due to the higher viscosity.

Bottom Line is that when you're checking to see if your oil pressure is consistent event to event, you should only check data points at high rpm (after the bypass is open) and when the oil is warm. Your pressure should be essentially constant during this window.

Duncan

To all this.

Low 30's hot is too low. You can cheat it up with heavier oil. It might run like that for a while but when the bottom starts to get loose it's a slippery slope.