disclaimer: sorry If this is in the wrong place for my thread, first time posting on any forums. if its wrong just tell me where to move it to, thanks.

So a little background first. about a year ago I blew the lm7 in my 99 Silverado and opted to rebuild it myself with the help of a family friend whos more experience than I. We decided to spice things up a little with a btr stage 2 gen 2 cam, new pushrods, Hastings piston rings, new standard size Clevite bearing all around, and a Melling high volume/pressure oil pump. the build went good with no major hiccups.

I noticed that the oil pressure is doing some weird things I wouldn't expect it to. So at cold start everything seems fine with pressures around 40-43. due to oil thinning as it warms up id expect it to drop some but its dropping down to around 18-20 when fully warmed up with my idle set around 650-675. now it immediately goes up with any throttle. after warmed up, pressures are around 18-20 at idle, around 1000-1100 itll sit at 32-35 and at 1600+ itll sit right at 40-43. these r constant numbers when warm. It just feels weird to me going from a 40-50 system before rebuild to a 20 idle after. we checked ALL clearances and they were all within spec so I cant be losing pressure there. the rod bearings were a hair in the looser side but within recommended specs and this was verified by a local shop. we replaced the O-ring on the oil pickup tube with the correct one, and we put the dumbell in place. we did not modify the pump out of the box, it was unboxed, oiled and installed. forgot to mention im running 5w30 oil.

So my 2 main questions: first. I wasnt aware at the time that it is recommended to run a larger capacity oil pan to avoid oil starvation at high rpm. this isn't a major issue as the highest the engine will ever see is around 6000 for sub 5 seconds getting on the highway. this is a DD not a street truck. will running an extra .5 quart of oil suffice or will that hurt anything? I really don't want have to tear the front of this engine apart again to change the pump, or buy a new pan.
second. Can anyone give me any incite on my oil pressure "issue"? If it even is an issue. It just feels like its running low considering its a high volume high pressure pump.

 

Been doing the GMT-800 truck stuff quite a while. Can't remember anyone going to a larger oil pan even with high horse builds. I'm running the factory pan 2000 GMC Sierra with a 6800 shift point and 7000 RPM limiter setting with zero issues of starvation. I understand the concern seeing the PSI lower than the original engine. I would be more concerned if it had a higher hot pressure then slowly falling off. It may be rod bearing clearances that's dropping the pressure, which I wouldn't worry about since they're in spec.

You've done the o-ring... did you replace the cam retainer plate? With old plates the orange gasket can be smashed flat and can dump some pressure from the oil galley. Two things I would do (since you said you're not changing the pump) buy a oil filter cutting tool and carefully inspect the filter element for bearing material, if good that should ease some concern. Then maybe swap to Mobil 1 European 0W-40 (cheap at walmart). It has a slightly higher ZDDP content and after testing it's closer to a 0W-35 viscosity which may bump up PSI.

 

Many times has an oil pickup tube o-ring installation gone bad for various reasons. Herre is info from Melling

 

OP said "Can anyone give me any incite on my oil pressure "issue"? If it even is an issue. It just feels like its running low considering its a high volume high pressure pump."
I don't think it 20psi @idle and 40-43psi off idle is normal for a high volume/high pressure pump. If it is actually a good working high volume/high pressure pump there is some other issue.
I have a high mileage LQ9 swap that I installed a Summit brand high volume pump. I did add a thin washer to the by-pass spring to increase the by-pass pressure point. My oil pressure reads no lower than 48psi @ operating temp idle.
I know you stated bearing clearances were checked and are within spec. That would only leave a few possibilities. Pump o-ring, cam end plate seals, barbell? Are you using the same oil pressure sender and gauge as before the rebuild?

 

I am using the same gauge and sender as before. it was just a basic rebuild where we pulled the engine from my truck, took it apart, rebuilt it, and reinstalled it. I'm almost to the point of rechecking bearing clearances because its getting on my nerves. even if its not, I feel like the thing is gonna cook another rod bearing.

 

that makes me feel better about the oil pan. The next time I do an oil change Ill use that oil and check the old filter for particulates.

 

I agree on 0w-40. Been running it in my LS C5 for over 15 years. Im glad it's now available in the 5qt containers! When I started running it, it was only available in quarts. Great cold flow with the 0w, and the protection of 40 weight when hot. What's not to like?

 

i was going to ask this marked in Red

 

I also think there's something wrong with those numbers on a Melling "high pressure high volume" pump.

Actually, I don't see anything in this build that would've pushed me to a high volume/high pressure pump. I generally prefer a stock volume, stock pressure pump, although I usually go with the Melling "stock replacement" units because they resolve a cavitation issue at high RPMs that's present in the factory original pumps.

You also didn't mention what oil filter you're using. An AC Delco filter is inadequate for the stock volume pump. With the AC Delco filters, the bypass valve opens between 2800 and 3500 RPMs depending on oil condition and a few other variables. For daily drivers, this usually isn't an issue. Unfiltered oil at rare times when the engine is in higher revs is better than no oil, and daily drivers with "normal" driver habits rarely see the high side of 3500 RPMs. IIRC, the Wix 51042 (or 51552) filters are rated for ~10gpm (compared to ~3gpm for the AC Delco PF-46/PF-46E)

I don't think a higher capacity oil pan will help, either. I think you've got some leakage inside the engine allowing pressure to bleed off. I'll agree with those who suggest the cam retainer plate O-ring could be a problem. There are a couple of other potential problems, but that one is the most obvious and most likely.

 

sorry for late reply. since this was my first rebuild I just kinda went for it. I was relying on my family friend to guide me if I got anything wrong (like a stock replacement vs hv/hp oil pump). Knowing what I know now I would have done a number of things differently, like phisically measure and note clearances and realizing I don't need that crazy of a pump for the app. I did replace the cam retainer plate and torqued it accordingly so I dont think it would be bleeding pressure from there but who knows (i dont). I do run a acdelco filter the longer one, not sure on part number. that is correct in your assumption that it doesnt see above 3500 much, though I do some spirited rolling starts sometimes. so since ive got the hv/hp pump, It sounds like the wix would be a bit better filter option for me. is that correct?

 

@Krow
To answer your questions.

1. I never recommend an inadequate oil filter. I always go with one that will filter the full flow of the oil pump. So yes, a Wix is a much better choice.
2. An extra half quart of oil is probably a good idea. In the autocross car that runs an LS1, we start the day with a full quart over the "full" line. I believe that C5 Corvettes with the LS1 recommended that extra full quart "for track use or competitive driving." We've never had a foaming issue with that. It does consume oil through the PCV system (which we still have unmodified). We use about a half quart of oil on 8 to 12 runs around the parking lot (usually a little under a mile per run, mostly in 2nd gear). On "test and tune" days when we get a lot of runs, we tend to check and top up a few times during the day.

 

much appreciated on the incite, thanks!