[grivera]

Looking for an opinion on an oil pressure issue. Build sheet indicates main and rod bearing clearances are both .0025. Melling MEL-10541 80 psi pump with a 19/32 relief ball, factory style pick-up tig welded to pump. AC Delco PF24 oil filter; bypass in filter housing intact. Oil is conventional 10W30.

Factory style oil pan, 6 quarts of oil. Engine has about 600 easy miles on it. Oil sending unit is mechanical via analog gauge and 1/8" copper tubing.

Cold high idle is 90 psi and hot psi before a drive is 20 at 900 rpm. On highway, cruising well heat soaked at 2500 rpm - 50 psi oil pressure. When heat soaked after a drive, idle in park is 12-15 psi at 900 rpm. With engine hot, stabbing of the throttle in driveway with trans in park will take oil pressure up to 70 psi. Free-With a test gauge at the oil
filter housing port, the idle psi is about the same as the interior gauge. I haven't used the test gauge while driving as the line is too short.


My main concern is under load. If I cruise for a while at a steady rpm with the engine at full temperature (180-190), the psi drops. Say at about 2800-3000 rpm oil pressure will drop as low as 45. If I stab the throttle a bit it will go to 60 psi and will climb to about 70 psi if the rpm is 4k going up. The main issue is at steady highway rpm on a heat soaked engine. This characteristic has existed since the engine was a fresh build.

I have tried 15W40 oil and results are only slightly better but certainly not seeing 80 psi on the gauge during high rpm on hot engine while driving.

There are no noises, rod knocks, etc. Oil filter inspections have been negative for metal.

Could this be a stuck check-ball?

[dataway]

10/30 seems pretty light to me. 50 psi doesn't seem out of line for 2800 on a hot engine.

I'm not sure on this ... but isn't .0025 on the loose side for a street engine?

If you are using a smaller check ball and didn't shim the spring that will lower pressure some, and if the check ball seat is irregular you'll lose some pressure there. I'm kind of a fan of lapping the seat with a 19/32 ball before using one since the seat is originally designed for a 5/8 ball.

But jeez, doesn't sound like you have any major problems. I'm sure someone that knows a lot more than me will comment.

[Half-Inch Stud]

My opinion is the dominant leakpath would be the (clapped-out) cam bearings. Do them yourself next time.

[grivera]

Originally Posted by dataway

10/30 seems pretty light to me. 50 psi doesn't seem out of line for 2800 on a hot engine.

I'm not sure on this ... but isn't .0025 on the loose side for a street engine?

If you are using a smaller check ball and didn't shim the spring that will lower pressure some, and if the check ball seat is irregular you'll lose some pressure there. I'm kind of a fan of lapping the seat with a 19/32 ball before using one since the seat is originally designed for a 5/8 ball.

But jeez, doesn't sound like you have any major problems. I'm sure someone that knows a lot more than me will comment.

I didn't shim the spring as the ball is only 1/32" smaller than the standard size ball. Always thought .0025 mains and rods are a happy medium.

Originally Posted by Half-Inch Stud

My opinion is the dominant leakpath would be the (clapped-out) cam bearings. Do them yourself next time.

Would there be any metal in filter if this was the case?

[gtofreek]

Sounds pretty normal to me for that weight oil. When hot, that thin of oil is like water. Hard to make pressure like that. We always use 20/50 here for that reason. 10/30 just won't make good pressure in the heat. It just bleeds out of the bearings and leak points too fast to make 80 PSI. You don't need 80 PSI anyway. Have you tried 20/50? My 428 in my 65 GTO would only have 5 PSI at idle with 20/50 when hot. It would make 20 PSI cold, at idle. I went to straight 50 weight racing oil and it would make 15 PSI at idle. It would always jump right up to 60 PSI when I hit the gas, but next to nothing at idle. After many years of very hard running and with a big shot of nitrous for a year and a half, all the bearing looked great except for the slight wear on the upper rod bearings from the years of detonation it endured being it was a 12:1 compressioned engine I ran pump gas in. That was in the 80's, and years before I was an engine builder, but that engine ran strong, and it's only demise was the stock exhaust valve loosing it's head, and sticking in the piston. It's funny because the exhaust valve broke right where the stem is welded to the head, but yet the stock intake valve was bent into the shape resembling a lightning bolt, and shoved back up into the intake port, but it never broke.

[steve25]

Everything sounds fine with the oil pump and your pressure concidering the 10W30 oil, but with your Bearing clearance's getting on the big side like they are I would run nothing less then a 20W40 oil!

Also the long 4.210" stroke puts a lot more heat into the oil faster then a 3.750" stroke.

[Riku]

You need thicker oil for those bearing clearances. Quality 20W50 is spot on for you.
I run only 20w50 in my engine. My bearing clearances are between .0025 - .0026 oil pressure is perfect in all rpms.
.0025 is good clearance for hi-perf street engine.

Riku

[grivera]

I have a hard time wrapping my head around this being normal but will give the thicker oil a try. My numbers matching 400 has same bearing clearances and with a 9/16 ball/shimmed spring pushes 30# at hot idle and 60# anything above 12-1500 rpm.

What 20w50 do you run - looking for a decent one to try locally available.

[Riku]

I run Penngrade1 or Kendall GT-1 Competition. Penngrade is keeping oil pressure slightly higher than Kendall in my engine when hot.
https://penngrade.com/penngrade-1/
https://www.kendallmotoroil.com/prod...iquid-titanium

Riku

[Jay S]

My guess is the rotating assembly has more side clearence on the rods and makes it harder to build oil pressure. You could tighten up the oil clearence to .002 and it would be almost the same. Especially with cross drilled cranks. It is totally normal. We set up all the performance engines with .0025 rod clearence and run 15w40 stock build to 20w50 for performance. I completely agree, Switch to 20w50. We usually run a 20w50 semi synthetic valvoline and Kendall the majority of the time. Jay

[lfdsteve]

Fwiw I had a similar issue. I upped to 20/50 and also did a bit of clean up in my e heads as they seemed not to want to let go of the oil and it just pooled on top.
Made a huge difference.

[grivera]

Looking forward to trying the thicker oil - a bit concerned of viscosity with the 80# pump though.

[STEELCITYFIREBIRD]

Be nice to it till oil is up to temp.
I wouldn’t sweat the pressures your seeing. Did you get # on rod side clearence when assembled?
Keep an eye on dizzy gear wear!

[grivera]

I do have the measurements on the rod side clearance-Need to pull the paperwork

[chiphead]

Cam bearings do have a significant impact on hot oil pressure. 20W50 just seems thick for a street motor in the winter. No worries about cold oil flow? Is there a good 10W40 or 15W50 oil that would be a good compromise?

My new motor is .0025"-.0028" on mains and .0023" on rods, .030" rod side clearance. I installed the 9/16" ball and a .055" shim, and verified I get 70PSI with 10W30, during an oil pump test on the engine stand. So I'll be in the same boat when I get this motor in service.

[hurryinhoosier62]

I ran 20W-50 in my ‘72 GP with no problems. It was my daily transportation from ‘88-‘90. My main and rod bearing clearances were .0025 on the mains and .002-.0022 on the rods.

[tom s]

The only time the factory used a 80 lb pump they used a larger dist gear!Engineers do things for a reason!Just saying.Tom

[grivera]

I know, I know...was talked into it by my builder- also, JBP recommends the 80# with long stroke engines. If I end having to drop the pan I will replace with a 60# pump...

[Steve C.]

Butler information in post number 2 here along with additional related material of interest......

http://forums.maxperformanceinc.com/...t=bearing+wash


.

[gtofreek]

Just don't wrap on the throttle when cold and you'll be fine. Let the engine idle and warm up some before getting on it. Even 20/50 gets pretty darn thin when hot. We use only Brad Penn, or Penn grade 1 as it's known by now. Great oil with very good cling-ability. As far as I'm concerned, it's the best oil on the market. It also has a high flash point so if you develop a leak on the header, you usually don't have to worry about it catching on fire and burning your car down.