Pressure drop along oil galley? Filter/cooler

[CJK440]

Not sure if this is the right forum but here goes.

I have a corvette I bought that has a shop built 540hp LS2 so I do not know any bearing clearances etc. I'm running VR1 10-30 with a Wix XP filter. The car has an OEM Z06 oil cooler which I believe on the LS has 100% of the oil routed through it after it goes thru the filter.

Anyway I have an autometer electrical gauge mounted on the drivers front port near the pump (Melling std vol/hi pressure) on an AN adapter that also hooks to my Accusump. This location is before the filter/cooler right near the pump outlet. This gauge (which reads similar to the accusump mech pressure gauge) reads about 10psi higher cold and 20psi higher hot (20 min commute) vs the factory sender that is located at the rear of the block (post filter/cooler). I put a new OEM sender in to be sure. After back to back hot laps @ autocross I witnessed the factory gauge drop down to 16psi at 800 rpm idle with 218 oil temp and shut it off as it was under that rule of thumb 10psi +1 psi per 100 rpm (aftermarket gauge was reading healthy, maybe 35 ish).

I'm assuming that the filter and cooler are a restriction that the pump is pushing against which leads to higher oil pressure reading that doesn't change too much with oil temp. However, post filter and cooler, as the oil heats and drops in viscosity flows through bearing/lifter clearances much easier and the cause for a larger reading delta the hotter the oil gets. But is 20 PSI at operating temperature reasonable?

A large percentage of people who track their corvettes suggest a 0w40 or 5w40 for track duty (some saying 50) to work better with elevated oil temps and I am going to try the latter with an AC Delco Ultraguard filter. I'm sure it wont change the differences between the two gauges, but hope at least I will see more comfortable hot idle pressure readings.

 

[Trav]

Not sure if this is the right forum but here goes.

I have a corvette I bought that has a shop built 540hp LS2 so I do not know any bearing clearances etc. I'm running VR1 10-30 with a Wix XP filter. The car has an OEM Z06 oil cooler which I believe on the LS has 100% of the oil routed through it after it goes thru the filter.

Anyway I have an autometer electrical gauge mounted on the drivers front port near the pump (Melling std vol/hi pressure) on an AN adapter that also hooks to my Accusump. This location is before the filter/cooler right near the pump outlet. This gauge (which reads similar to the accusump mech pressure gauge) reads about 10psi higher cold and 20psi higher hot (20 min commute) vs the factory sender that is located at the rear of the block (post filter/cooler). I put a new OEM sender in to be sure. After back to back hot laps @ autocross I witnessed the factory gauge drop down to 16psi at 800 rpm idle with 218 oil temp and shut it off as it was under that rule of thumb 10psi +1 psi per 100 rpm (aftermarket gauge was reading healthy, maybe 35 ish).

I'm assuming that the filter and cooler are a restriction that the pump is pushing against which leads to higher oil pressure reading that doesn't change too much with oil temp. However, post filter and cooler, as the oil heats and drops in viscosity flows through bearing/lifter clearances much easier and the cause for a larger reading delta the hotter the oil gets. But is 20 PSI at operating temperature reasonable?

A large percentage of people who track their corvettes suggest a 0w40 or 5w40 for track duty (some saying 50) to work better with elevated oil temps and I am going to try the latter with an AC Delco Ultraguard filter. I'm sure it wont change the differences between the two gauges, but hope at least I will see more comfortable hot idle pressure readings.

I think 10psi for every 1000 was the rule of thumb. 10psi for every hundred would be 200 psi for 2000 rpm or 500 psi for 5000 rpm, that would probably blow the oil cooler into the next steet. I read this..

GM states 6psi per 1,000 is the absolute minimum, 10psi per 1,000 rpm is the recommended rule of thumb according to the GM Service Manual

 

[CJK440]

I think 10psi for every 1000 was the rule of thumb. 10psi for every hundred would be 200 psi for 2000 rpm or 500 psi for 5000 rpm, that would probably blow the oil cooler into the next steet. I read this..

No not 10psi/100rpm. What I always followed with old school V8's was 10psi base to start + 1psi per hundred rpm so my 800 rpm idle would want no less than 18psi.

GM states 6psi per 1,000 is the absolute minimum, 10psi per 1,000 rpm is the recommended rule of thumb according to the GM Service Manual

Now if GM's guidance you posted doesn't consider a base to start from and just a flat 6psi/1000 min and 10psi/1000 desired, 16psi at 800 shouldn't be a worry. Maybe new tech is more tolerant. Still scares me.....

 

[fantastic]

Have you tried a 40 or 50 grade & seen what the PSI shows? Give it a try & see what you think. I think for that amount of HP it would be a good idea to use 40 grade at the minimum.

 

[CJK440]

Have you tried a 40 or 50 grade & seen what the PSI shows? Give it a try & see what you think. I think for that amount of HP it would be a good idea to use 40 grade at the minimum.

I've got 5w40 synthetic ready to go in. Perhaps the build required this in the first place. The only thing I had that pointed to a 30wt was an invoice that showed 30wt break in oil.

 

[fantastic]

I've got 5w40 synthetic ready to go in. Perhaps the build required this in the first place. The only thing I had that pointed to a 30wt was an invoice that showed 30wt break in oil.

That makes more sense about the break-in oil. Right, don't worry about the break-in viscosity if that has already been run. Any UOA planned for this roadster?

 

[johnmyster]

Flow resistance will drop across the filter element and oil cooler when hot, for the same reason it drops everywhere else (bearings, orifices, piston cooling jets, etc.)

Flow resistance across every item in the circuit is literally f(flow, viscosity) and in some cases also a function of RPM.

My LBZ would idle at 17 psi on 15w-40 at operating temperature and that was with the piston squirters shut down. Even less if it had to idle after pulling a grade without time to get the oil temp down. That same engine was 80+ psi at cold idle. Pressure due to temperature/viscosity swing can be huuuge.

I wouldn't trust the factory sending unit/gauge to be super accurate or even linear vs temperature. At high RPM do the two gauges converge? You'd expect the system to "back up" at higher pressure and be more uniform throughout if flow losses were actually the cause of having pressure differentials throughout.

 

[CJK440]

Flow resistance will drop across the filter element and oil cooler when hot, for the same reason it drops everywhere else (bearings, orifices, piston cooling jets, etc.)

Flow resistance across every item in the circuit is literally f(flow, viscosity) and in some cases also a function of RPM.

My LBZ would idle at 17 psi on 15w-40 at operating temperature and that was with the piston squirters shut down. Even less if it had to idle after pulling a grade without time to get the oil temp down. That same engine was 80+ psi at cold idle. Pressure due to temperature/viscosity swing can be huuuge.

I wouldn't trust the factory sending unit/gauge to be super accurate or even linear vs temperature. At high RPM do the two gauges converge? You'd expect the system to "back up" at higher pressure and be more uniform throughout if flow losses were actually the cause of having pressure differentials throughout.

I understand and do see pressure lower on both gauges with temp, can't tell if its proportional but perhaps. I guess I am less concerned about the drop due to temp but more so the pressure drop between the two readings assuming they are accurate. 20psi seemed like a lot with the filter and oil cooler in between. But the OE cooler looks like small 1/2" OD hard lines and am aware of a company offering a thermostat controlled adapter block and larger AN flex hoses that claims less pressure drop, ~5psi also has a place for a sender post filter. Might be worth it for piece of mind especially since I plan to track it.

I did change over to 5w40 and gained a couple PSI at idle. 30/32psi on the cluster (+4) and about 50 at the pump @190F (same temp as before). I also bumped idle RPM from 8 to 900 but that didn't seem to make a diff. I'm doing another auto X event in a couple of days and will see how the idle pressure reads after a few thrashings with even higher oil temp.

I'll have to do some tests to see if the delta reduces under high RPM.

Maybe I am just overthinking this.

 

[CJK440]

Actually at higher rpm the difference is larger. 35psi @2500 and 60 at the pump.....

 

[johnmyster]

GM is well known for making their factory gauges be inaccurate, in the more stable direction, in order to keep the drivers from being alarmed.

For instance, reads higher than actual temperature until up to operating temperature, then reads lower when above.

If you looked at the factory sending unit via scantool rather than the dash gauge, I'd suspect this to be the case.

 

[CJK440]

GM is well known for making their factory gauges be inaccurate, in the more stable direction, in order to keep the drivers from being alarmed.

For instance, reads higher than actual temperature until up to operating temperature, then reads lower when above.

If you looked at the factory sending unit via scantool rather than the dash gauge, I'd suspect this to be the case.

I've heard all manufacturers do this to "smooth" gauge movement as not not freak out your regular consumer just as you said.

I do have a tech2 and would be curious if it reports a different pressure than the cluster.

I think what I need to do is get the Autometer gauge into the oil passage post filter/cooler. Not sure if I can tee off the OE sender location at the top rear of the block.