So last spring I noticed an intermittent low oil pressure light when it was cool outside during the first start usually only lasting a second or so, when I slowly purchased items to fix it in case it got worse . I've put prob 8K since I first saw it but the other day I noticed the pressure dropped to around 25 while driving it was also moving ever so slightly up and down so I decided to check it out . I removed the oil pan, and the pump and didn't see anything out of the ordinary I even checked to see if any cam bearings had moved. Planning on a new oil pump timing chain, and maybe an analog oil pressure gauge, and trying my best to clean out the block passages as best I can while I have access to them.

I am curious about the new oil pump I got from Rock Auto it's a genuine GM Part number 127103303 on the site but it is a Melling M295 with the GM part number good thing I checked I would have hated to install it with the wrong o-ring after all that work, has anyone else seen a melling pump with GM part number on it?

 

No idea on the part number but a very common issue is the o-ring on the oil pickup tube gets hard and causes weak oil pressure on the gen 3 LS engines which might very well be your issue.

 

Im hoping its that or maybe I had a weak pressure regulator spring

 

A few thoughts:

Replace oil sending unit and remove debris screen below it. Research the internet to see what I'm talking about.
Check oil filter bypass pressure. Not all filters are created equal and I found the best filter for my old rig was a Baldwin ir the Wix XP filters.
The Melling pump is more or less an OEM item but R/R o ring as others have stated 1st.

Good luck

 

Thanks, I replaced the oil-sending unit, no filter under it, I had a Wix filter on it, But I May have found my issue, The low oil pressure was a quick display and happened when I added an after-market engine oil cooler block to re-connect my oil cooler in the radiator, I had a thread on it earlier this year asking the forum if the factory one had a pressure switch or thermostat in it with no luck with responses, however, I believe it does, and looking at the path the oil takes it would go to the oil cooler first before it dumped down to the filter aka the quick light, I'm hoping that is the case when I put it together I'm going to block it off for the time being while I figure a solution maybe find one that has a thermostat that opens up. Now the sudden drop from 40 to 30 ish I hope the pump and oring take care of that, I will also be testing it with an oil pressure gauge once it is back together.

 

If you wouldn't mind, can you provide me with your diagram for the oil paths? Also what adapter are you using? I am about to replace my factory cooler lines with some -10an lines and an Earls oil cooler adapter. I dont want to run into the same issue, but the factory one looks like it is straight through. And please update us when you get it all together.

Also drop from 40 to 30ish? does that mean you had 40psi before and now its at 30? is this at cold start, or after its fully warm? Idling or cruising? I think mine sits at like 50 on a cold start and about 25 idling while warm.

 

I'm finished with the oil pump and here is my current setup

It Has an M295 oil pump, I also added two 5mm washers on the pressure relief spring to get a little more pressure out of it, I also installed an Autometer oil pressure works off a braided line from the oil priming port and oil pressure temp gauge, Last added a derale oil block with thermostat. When it starts pressure is around 55 PSI and drops down to around 40 at idle once it's warm, driving oil is at 50 PSI @ 2000 RPMs