65LSXNOVA

Got a weird oil pressure problem. Looking for some insight. He's what I have and what I'm dealing with. 6.2L stock bottom end rebuild with maybe 700 miles on it.
Main bearing clearance where .0017-.0018. Rods .0024-.0026 melling .
Melling 10295 pump
New barbell.
DOD plugs and cover
New oil pressure sensor and i confirmed its accuracy at ilde and parked reving with a mechanical gauge.
Used sae 30 on first 10 miles then dumped oil and cut filter. Very little trash in filter.
switched to 15w40 and a wix non bypass oil filter.
Cold idle pressure 75psi
Warm idle pressure 50psi
cruise pressure. 65psi
Slowing rolling into throttle to 5000 rpms will net 95 + psi
Now here is where the **** starts getting weird. If I'm in 2nd and floor it it'll climb to 75psi or so then drop lile a rock to mid to high 50s. As soon as i let out to shoots back up. Thought i was low on oil so i checked it. Dead on level....so i added a qt more and same results. Ebay fbody pan with the bypass blocked also.

Tramminc

Either the motor is in fact low on oil, the oil pump could be failing or not pumping oil sufficiently or the oil pressure sending unit is not working properly and may be producing a faulty reading.

Sounds like oil not returning to the pan fast enough, or simply too much windage from no tray, causing foaming. I'm betting on windage/foaming. Look into Milodon's Diamond Stripper windage tray/screen. It mounts to stepped down main studs. In the case of windage, more oil can work against you, and cause even more foaming. Hope this gives you something to consider.

grinder11

iTrader: (1)

I'm betting on foaming along with you. Also-To the OP; why in the world do you want 75psi oil pressure? It's bleeding more power than you think. Anything over 60psi in the LS engines is more problems than benefits, one of which you're probably seeing now. I run the 10296. If I had to guess, you're also running the high pressure spring. The 10296 comes with a std. spring, and a higher (stiffer) pressure spring. I don't know if the 10295 comes with an extra spring, or not. Been too many years since I've read up on them, but I know Melling supplies 2 different rate relief valve springs for the 10296, one is installed, the other is extra. IIRC, the standard pressure spring comes installed. I'm guessing a high pressure spring is in the pump, and may have been shimmed, further increasing pressure. NOBODY needs 75lbs cold idle pressure, and 50lbs hot is also extreme......

65LSXNOVA

I much appreciate the answer...
Has there been a test of HP lose from oil pressure going from something like 60psi to 95psi? I've yet to see or read that other than internet here say.
Could running a truck windage tray instead of the fbody windage tray on a fbody pan cause this?

Full Power

You are running out of oil in the PAN at high rpm, 15W40 DIESEL weight oil is "Stacking Up" top of the engine.
Try the same operation with 5W30, I'll bet the problem goes away.

G Atsma

^^^^^^^^^^THIS^^^^^^^^^
15/40 is way too viscous for LS engines. Plus the diesel spec is wrong for gas engines.
If anybody thinks I'm wrong, summon Polyalphaolephin and ask him.

65LSXNOVA

Im thinking of running a 5w20 or 5w30 on next oil change. I've read all the back and forth posts on diesel oil in gas engines. It just seams like a windage problem since the pressure jumps back up the instant I left off the gas.
I'm really wondering if it has to do more with the truck windage tray rather than the fbody one.

99 Black Bird T/A

iTrader: (4)

As mentioned, I'd try an oil change to 5w-30 and see what happens.

01CamaroSSTx

iTrader: (3)

You should try the 5w30 and see if that clears up your low pressure at high RPM. I ran into this issue with the 10296 pump and the fbody pan and windage tray but it had nothing to do with either of those it was insufficient pickup tube to pan clearance that caused my low oil pressure at high RPMs. 1/4 inch wasn't enough and it needed more like 3/8.

65LSXNOVA

I just read a article stating 3/8" to 1/2". I guess I'm dumping the oil this weekend and dropping the pan to check pan to pickup clearance.

Floorman279

iTrader: (11)

its hidden in ls1tech land, but the few wise ones on here say if you wanna run a 10296 pump, you need a deep sump pan. i had a similar issue but worse, switched to a deep sump pan, problem solved

Che70velle

iTrader: (6)

I’m prolly on the tighter side of clearance, and my pickup is .235 from the pan floor. 10296 pump. Gibbs LS30 oil exclusively. Zero fluctuations on oil pressure regardless of rpm. I absolutely will not go over 3000 rpm until oil is at temp, which for my setup is 185-190.

jayyyw

I ran 20w-50, 10296 pump, corvette pan and windage try. No issues with pressure fluctuations like you describe. Might have to do with the "ebay" version of your pan.

FormulaBoat

iTrader: (1)

If suspect windage, run one quart low and see what happens. If the pressure drops less or more, it may help to give you a better idea. Obviously don’t hold it long or let it dip low if it drop further below what you already are seeing.

I would also try to replicate the pattern in neutral and then under driving load to try and help figuring it out.

Some good experience tips posted above though.

Sunset01Z

iTrader: (1)

So why are you running a high volume pump with stock clearances? This has been known to cause issues and adding 15/40 further contradicts it. You're basically forcing thicker oil at a faster rate. I'd switch to 5/30 as the others said and test it. This high of pressure affects everything and is not always a benefit.

65LSXNOVA

I just edited my post. During the build I was going back and forth between the 10295 and 10296 pumps. I looked back at the paper work and it was a 10295 I installed..

grinder11

iTrader: (1)

I also believe the viscosity is wrong, and even if it's changed to the right viscosity, he's still going to have WAY too much oil pressure. 95lbs is ridiculous, don't you think? Sure, a lower viscosity will help, but he is still running a 40 weight oil with 15w-40. Yes, it's a tad thicker than 5w-30 or 10w-40. I ran 15w-50 years ago in a Darton 427, with a 10296 and standard spring. I never saw close to 95lbs, and, like you, I had no inconsistencies. IIRC, isn't the 10295 the high pressure Melling? Almost sounds like he, or someone, has shimmed the already stiffer relief spring. He shouldn't be worrying about hp loss (yes, I brought it up), because that's the least of it. The worst of it is the undoubted aeration of the oil. Atsma made a good call on Poly-Hope he chimes in.

grinder11

iTrader: (1)

Why not run what the engineers recommend, a 5w-30? If you want 40 weight protection, and good cold flow, go with what I did back in 2005-0w-40 Mobil 1. I really think someone-You or the builder, has shimmed the relief spring for too much pressure. Even if you're not running the pan dry, you're aerating the oil, which causes higher wear on the plain bearings, cam, main, and rods.......

lazaris

iTrader: (5)

This is most likely the cause. The reason being the oil pressure immediately jumps back up when you lift the throttle. The pump slows down enough to stop cavitating because of the lack of clearance between the pick up and the pan. A lot of people say you can suck the pan dry, but if that were the case and you had say 3 or 4 quarts of oil still up in the heads when you lifted the throttle, there would be no way that oil would return to the pan in a split second for the pressure to instantly shoot up when you lifted. The higher the volume pump the more clearance you need. The 10355 and the 10355HV may need at least 1/2". As 01CamaroSS states, try 5w-30. If your pressure does not drop as much you know you need more clearance because the lighter weight oil was able to flow into the pick easier and reduce cavitation.

grinder11

iTrader: (1)

I've been running the 10296 in the "batwing" C5 oil pan for years, and it's never cavitated. It's not exactly a deep sump, though there is a deep-er part that the pickup is in. One thing I'd like to say about the LS high volume pump. Pressure is pressure. What I mean is, bearing clearances will dictate what pressure the pump generates. You will get x amount of oil thru the bearings at 45psi. Let's say it's 5w-30. You won't get any more volume of oil thru the bearings at 45psi with a high volume vs a std pump. The pump can only flow so much oil past the bearings. The extra will be bled off by the relief spring Where a high volume pump comes into play is higher pressure at idle/lower rpm, looser bearing clearances, piston oil squirters, or quicker recovery of oil pressure if you've experienced high lateral g-forces. At 45psi, the high volume pump will put no extra oil thru the engine than a std pump, because the bearing clearances dictate a fixed number of gallons per minute at any given pressure. If you run a stiffer relief spring, then the high volume pump will be capable of flowing more oil, but so will the standard pump. I hope this makes sense, but somehow I don't think I've done a very good job of conveying what I'm trying to say. I will say this; I've spent many years at the strip, and had a lot of friends running hi volume pumps. I've never experienced, nor have any of my friends experienced, pumping the pan dry. I guess it's possible, at a sustained high rpm, with oil that's too thick, with an inadequate oil pan capacity, with a shimmed relief spring, with the pump cranking out 100psi. Still, nobody I know has ever had the sump run dry due to having a high volume pump.......