Another Oil pressure question, do I need a heavier oil?

[Turbo6inKY]

I promise I searched. Lot's of people asking about idle pressure, and they are mostly viewing it at the gauge.

I finally got a pressure sensor plumbed in and I'm datalogging it, and I'd like a few extra experienced eyeballs to take a look at this plot from a drive today.

White is coolant temp, red is oil pressure in PSI, and green is engine RPM.
Max and min are at the left. My max oil pressure was 63.4psi when it was cold (but probably 30-40 seconds after start, I didn't start the log until I was moving). Minimum was 15.4psi idling in the garage once I got back home, right before shutting it off.

The relatively smooth part in the middle is highway driving @ 65mph. It started that phase at 43.6psi and trended downward until it leveled off at ~38.75, I'm guessing because that's when the oil temperature stabilized.

So the big question I have: does this look right? This is 10w30 Royal Purple on a 60 degree evening. Do I need to step up to a 40w for the summer?

Thanks!

 

[Boost231]

Do you have a oil cooler? If so which one or setup? Logging oil temp

Sent from my SM-G935T using Tapatalk

 

[Turbo6inKY]

Do you have a oil cooler? If so which one or setup? Logging oil temp

Sent from my SM-G935T using Tapatalk

Just the cooler in the radiator, which is a new monster GN1 job. Not logging temp yet.

 

[Turbo6inKY]

Here's a zoomed in snippet. This is me backing into my garage, which has a decently steep apron from the alley.

Cursor is at the low point, 14.2psi... but that was at just 650 RPM while I was lugging it up into the garage, which is all the finagling bracketed in blue crayon. Towards the right in red is the car idling after it was put in park. As the idle bounces around from 800-900rpm (closed loop idle, so it hunts a bit, and I probably need to re-set the IAC), the pressure is moving along with RPM, and averaged 17.27psi in that range.

 

[Gene Van Horn]

Its not high,should pin the gauge at cold start. Relativly steady, i would consider it alittle low, how many miles on this car? Also does it rise one to one when in boost, always have to check on that. A different oil may help when its cold but probably get the same results once it warms up. Might wanna check your compression, mine is at 20 when hot in park idleing with about 30,000 mile on it.

 

[earlbrown]

The old rule was 10PSI per 1000RPM. You're right at double that with quality oil.


Don't worry about it. You might get away with thinner oil if you wanted to try that and free up a few ponies.

 

[Turbo6inKY]

Its not high,should pin the gauge at cold start. Relativly steady, i would consider it alittle low, how many miles on this car? Also does it rise one to one when in boost, always have to check on that. A different oil may help when its cold but probably get the same results once it warms up. Might wanna check your compression, mine is at 20 when hot in park idleing with about 30,000 mile on it.

"Pinning the gauge" here would be 100psi. That's the limit of the sensor.

There's 10K on the engine. I rebuilt it after the OE head gaskets gave out at 69K. But it's been through a hard season autocrossing in that 10K miles. The big reason I rigged this up is when you're doing that, you can't look at the dash, so neither a gauge or idiot light is much help.

Not sure how much boost is going to affect oil pressure, it's obviously rising/falling right along with RPM, though.

My last oil analysis looked really good, but I'm due for a change next month. I'll have that sample checked, too.

I'm not terribly worried about the overall health of the engine. It's running fine at the moment. Now, if I find out over the course of the next season that I'm uncovering the pickup and losing pressure while racing it, well, I'll deal with that if it happens. Just wanted input on whether a 40 or 50w might be in the cards at the next oil change for some insurance, mostly because of the slightly low idle pressure.

But...

The old rule was 10PSI per 1000RPM. You're right at double that with quality oil.

These are the nuggets you miss when trying to search here. Board's been around so long there's a million threads. Earl's obviously providing some pretty strong temptation for me to succumb confirmation bias.

Here's a closeup of a bit from idle to 2800, pretty gentle acceleration up to ~30mph, the big drops in RPM are gear changes.

1975rpm of rpm rise along with 21.20psi, so right on the old rule.

I think the answer's going to be, "Keep an eye on it."

 

[earlbrown]

Your graphs aren't really what I'm used to looking at so I don't see the same thing as you do.

The 10 per 1000 rule is actually kind of outdated. It was written when oils aren't as good as they are now. Basically that means that the rule is now overkill to a degree.

On the oil change I'd at least go to a 0-30. No reason to have extra resistance to flow during startup. Actually, personally, I'd try a 0-20 if I had the logging software you have. I have a feeling you'll still have good pressure but run a little cooler and free up some HP.

 

[Gene Van Horn]

I apoligize for the one to one comment, thats fuel pressure. Must be the drugs im on this week. Im also on a weeklong mourning period for what the steelers called football yesterday.

 

[Wahoo]

Don't the bearing clearances determine the weight of the oil you need to use?

 

[Turbo6inKY]

Don't the bearing clearances determine the weight of the oil you need to use?

The answer to that is "it depends."
It's not just clearances, but also the volume your pump supplies.

I just wanted an educated eye to look at my pressures

 

[earlbrown]

Don't the bearing clearances determine the weight of the oil you need to use?

No. Unless they're out of spec and you have to start using Motor Honey.


The usage of the car (street .vs road race track) and the pumps relief valve determine the oil weight.

 

[Chuck Leeper]

Was the sensor checked for offset?