Is my oil pressure somewhat okay?

ZeeOSix

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Pressure is a measure of resistance to flow. The factors in that equation are the oil's viscosity, the oil pump (volume), and the restriction (oil galley/orifice). The oil pump and restriction are both constant so going to a higher viscosity will decrease flow, hence an increase in pressure. People put way too much importance on pressure. Flow is more important than pressure.
Actually, the flow will be the same at X RPM because it's a positive displacement pump (assuming no air is being sucked on the intake and pump not in pressure relief), so the increase in oil pressure is because of the increase of viscosity to force it though the same oiling system resistance. Forcing say 3 GPM through the oiling system of thicker oil will take more pressure than forcing 3 GPM of thinner oil.

I agree with all your other assessments that it's probably a leaky oil pickup tube O-ring. There was a TSB from GM about it on my LS6 way back, but my LS6 never showed any symptoms of that issue.

Something the OP might also try is to look down into the oil filler cap a few minutes after a cold start-up with a flashlight and see if the oil is visibly aerated, but if it's not major it probably won't be that visible.
 
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Jesseyourcalipers

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Actually, the flow will be the same at X RPM because it's a positive displacement pump (assuming no air is being sucked on the intake and pump not in pressure relief), so the increase in oil pressure is because of the increase of flow to force it though the same oiling system resistance.

I agree with all your other assessments that it's probably a leaky oil pickup tube O-ring. There was a TSB from GM about it on my LS6 way back, but my LS6 never showed any symptoms of that issue.

Something the OP might also try is to look down into the oil filler cap a few minutes after a cold start-up with a flashlight and see if the oil is visibly aerated, but if it's not major it probably won't be that visible.
So if it’s not visibly aerated do you think the issue isnt too bad a I can maybe put off dropping the pan until tomorrow ? Or bad idea? I have a few things to do today and my other car is being used.
 

ZeeOSix

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So if it’s not visibly aerated do you think the issue isnt too bad a I can maybe put off dropping the pan until tomorrow ? Or bad idea? I have a few things to do today and my other car is being used.
Here's a snip of a GM TSB. Doesn't list your engine, but showing what the TSB about the oil pick-up O-ring says. There might be a TSB for your year out there somewhere.

Are you hearing any engine noises like the TSB describes? If the oil was getting really aerated the lifters would probably make some noise.

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ZeeOSix

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My dad mentioned the pick up tube but could it be as simple as the o ring?? And I have just a brass fitting and a mechanical gauge hooked up.
Maybe I missed it, but did a mechanical oil pressure gauge connected directly to the engine gallery show the same as the dash pressure gauge?
 

Jesseyourcalipers

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Maybe I missed it, but did a mechanical oil pressure gauge connected directly to the engine gallery show the same as the dash pressure gauge?
My dash was busted like every early Nbs dash. Every once in a while my needles go bonkers then back to normal. So I have mechanical gauges for what I think are important. And I have no noise. Engine sounds perfect.
 

ZeeOSix

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My dash was busted like every early Nbs dash. Every once in a while my needles go bonkers then back to normal. So I have mechanical gauges for what I think are important. And I have no noise. Engine sounds perfect.
Got ya. So is the mechanical gauge the kind that has a tube the goes to the block and measures oil pressure directly, of does it have an electrical sending unit/sensor involved?
 

Jesseyourcalipers

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Got ya. So is the mechanical gauge the kind that has a tube the goes to the block and measures oil pressure directly, of does it have an electrical sending unit/sensor involved?
No it has a hose. It’s connected to a brass fitting that is the exact thread to the engine. I used all new fittings and hoses when I put the new gauge.
 
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It's not the o-ring, as stated the 4.3 is based off the SBC, that issue affected the LSX. How many miles are on the replacement engine? If it was mine I would run some MMO or Seafoam in the crankcase to help clean it out first and then try a 40w oil. If I had to guess I'd say that most likely the oil pump is a bit worn. The 4.3 usually gets a bad rep because it's not really a 350, it's a fine engine and will last for a very longtime and typically without too many problems. They really aren't too picky about oil either, any 5w30 or 10w30 would work well in that engine, I don't think the newer ones ever went to 20w.
 

OVERKILL

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It's not the o-ring, as stated the 4.3 is based off the SBC, that issue affected the LSX. How many miles are on the replacement engine? If it was mine I would run some MMO or Seafoam in the crankcase to help clean it out first and then try a 40w oil. If I had to guess I'd say that most likely the oil pump is a bit worn. The 4.3 usually gets a bad rep because it's not really a 350, it's a fine engine and will last for a very longtime and typically without too many problems. They really aren't too picky about oil either, any 5w30 or 10w30 would work well in that engine, I don't think the newer ones ever went to 20w.

This issue is still the very sudden change in oil pressure, which indicates an "event" of some sort. Perhaps something is jammed in the relief on the pump? Anyways, it warrants further investigation.
 
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FWIW my 1999 4.3 V6 (160,000 miles, Costco Dexos spec 5W30) has about 10 psi at idle and 40psi at 2000 rpm at "operating" temperature.
 

Jesseyourcalipers

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Holy **** there's a lot of misinformation in this thread. OP, you need to yank that 4.3 & toss in a LS motor. Then pull it & replace the O-ring.
I live in ca so that says it all lmao. I’m very happy with the 4.3. And I don’t use it much. It’s enough for me when I want to cruise around. I ahem know people that have gotten in trouble with smog. CARB is a hassle and a half. lol ca is ridiculous. Or I’d have some crazy swap like a 4bt twin turbo or some **** for the heck of it. I’m not trying to spend money at the moment as I have other projects and things going on. I do have a scylone turbo complete kit for it and I’ll eventually probably overhaul and do some work for the small turbo but the 4.3 was given to me and this truck is my mega cheap dirt and mud cruiser.
 
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I'd check the pick-up tube for restrictions. I had a sudden drop in oil pressure on a Ford engine several years ago. After removing the pick up tube/screen and cleaning it everything went back to normal.
 

Jesseyourcalipers

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I'd check the pick-up tube for restrictions. I had a sudden drop in oil pressure on a Ford engine several years ago. After removing the pick up tube/screen and cleaning it everything went back to normal.
Exactly what I’ll do when I get around to it! That’s what I’m hoping for
 

Jesseyourcalipers

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This issue is still the very sudden change in oil pressure, which indicates an "event" of some sort. Perhaps something is jammed in the relief on the pump? Anyways, it warrants further investigation.
But still getting pressure you think I’d be okay to use for a couple of days until I get around to it? I would think yes as it went down 3psi only. 16 at warm idle, 44 cruising under 2k rpm 48-50 cold idle
 
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But still getting pressure you think I’d be okay to use for a couple of days until I get around to it?
I think you'd be fine as long as pressure doesn't drop below 8-10 PSI at hot idle. When I had this problem on my Ford 1.9L I just watched the oil pressure. It never dropped dangerously low so I just dropped the pan and cleaned the screen at the first chance I got. The engine had 518K miles when I finally retired it and still had good oil pressure.
 
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Holy smokes, mountains out of mole hills. 10 psi at idle is absolutely fine, especially if it builds quickly once back on the gas. Worry about it when (if) it goes below 5 or 6.
 
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