Weird Oil Pressure?
Thread Starter
On The Tree
Joined: Mar 2007
Posts: 113
Likes: 14
From: Calgary, AB
Weird Oil Pressure? Installed a supposedly good LH6 from a seller, changed cam and installed new cam bearings (they were a little worn, not bad) deleted the AFM and installed in a 97 C1500 and shows LOW oil pressure. I do recall using 2 different lifter styles, slightly different oiling holes, didn't think it mattered... Tested with actual gauges, at cold idle with 15w40 it shows 40-45 psi at the front plug and 5-8 psi at the top. Runs great, does have some oil at the rockers. When I installed the Holley knockoff pan I pulled a couple of caps to check the rod bearings and they were perfect with good clearances. 8 original lifters, 8 good used lifters from another build. Once I saw that I did NOT pull any of the mains; I don't like to disturb factory assemblies without cause (may have to change that policy...)
After searching the forum a lot I have changed the filter, changed cam retainer plate (oil gallery plug is in place), and plugged the AFM towers. The original barbell is in place, I haven't touched it. I can't pull the pan with the engine in the truck.
Is there anything else I can check before pulling the engine? I suspect main/thrust bearings now but wanted to exhaust all the options first. I was SURE it was either the cam plate or the AFM towers but alas...
After searching the forum a lot I have changed the filter, changed cam retainer plate (oil gallery plug is in place), and plugged the AFM towers. The original barbell is in place, I haven't touched it. I can't pull the pan with the engine in the truck.
Is there anything else I can check before pulling the engine? I suspect main/thrust bearings now but wanted to exhaust all the options first. I was SURE it was either the cam plate or the AFM towers but alas...
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Thread Starter
On The Tree
Joined: Mar 2007
Posts: 113
Likes: 14
From: Calgary, AB
Pulled that blockoff and blew out the passage from the top down, seemed clear. Put the blockoff back on and, on a lark, blew air into the top gauge port (I have a 2ft hose on it.) Air blows directly out of the oil filler at full speed. So, pressure in the oil passages bleeds directly back into the crankcase, that's where all the oil pressure is going. Now just to figure out where...
Who has any thoughts? Valley cover gauge port O-ring missing completely as posted above? I'm pretty sure it was in there and it's a lot of work to check. What kind of leak would be that big? I thought maybe the barbell seal or something but I would think that would be a slower hiss.
Who has any thoughts? Valley cover gauge port O-ring missing completely as posted above? I'm pretty sure it was in there and it's a lot of work to check. What kind of leak would be that big? I thought maybe the barbell seal or something but I would think that would be a slower hiss.
Is the pan from the original engine? I recall a pressure relief thing inside the pan. Was never sure what it was.
Pan was from a 2010 Camaro, didn’t fit my car.
Just a thought.
Pan was from a 2010 Camaro, didn’t fit my car.
Just a thought.
Launching!
Joined: Oct 2022
Posts: 206
Likes: 74
From: FL
Pulled that blockoff and blew out the passage from the top down, seemed clear. Put the blockoff back on and, on a lark, blew air into the top gauge port (I have a 2ft hose on it.) Air blows directly out of the oil filler at full speed. So, pressure in the oil passages bleeds directly back into the crankcase, that's where all the oil pressure is going. Now just to figure out where...
Who has any thoughts? Valley cover gauge port O-ring missing completely as posted above? I'm pretty sure it was in there and it's a lot of work to check. What kind of leak would be that big? I thought maybe the barbell seal or something but I would think that would be a slower hiss.
Who has any thoughts? Valley cover gauge port O-ring missing completely as posted above? I'm pretty sure it was in there and it's a lot of work to check. What kind of leak would be that big? I thought maybe the barbell seal or something but I would think that would be a slower hiss.
I run a Holley knock off pan, it uses no bypass but it recommends the pf63 or pf48 or similar filter and they have an internal bypass.
Thread Starter
On The Tree
Joined: Mar 2007
Posts: 113
Likes: 14
From: Calgary, AB
The filter should have an anti-drainback valve, so air/oil pressure applied in reverse should stop at the filter, no?
In any case, the air comes out of the filler tube with pretty much no restriction at all, it's a single giant leak.
In any case, the air comes out of the filler tube with pretty much no restriction at all, it's a single giant leak.
Launching!
Joined: Oct 2022
Posts: 206
Likes: 74
From: FL
I was just thinking about what I thought would happen.
So I went out and tested it. This is on a perfectly good running 5.3 that was removed for a 370. It had very good oil pressure. I put the stock pan back on it to keep it closed up.
I had to remove the timing cover to get to the second bolt of the holley knock off oil pickup tube so I taped the front seal up for this test. It is a gen 4 oil pan but the internal relief valve is removed and plugged. Because I did run it with this pan before the swap pan.
Putting air into the top oil hole makes it come out the dipstick tube. Even with the valve cover tubes wide open.
So I went out and tested it. This is on a perfectly good running 5.3 that was removed for a 370. It had very good oil pressure. I put the stock pan back on it to keep it closed up.
I had to remove the timing cover to get to the second bolt of the holley knock off oil pickup tube so I taped the front seal up for this test. It is a gen 4 oil pan but the internal relief valve is removed and plugged. Because I did run it with this pan before the swap pan.
Putting air into the top oil hole makes it come out the dipstick tube. Even with the valve cover tubes wide open.
Thread Starter
On The Tree
Joined: Mar 2007
Posts: 113
Likes: 14
From: Calgary, AB
Interesting. That much air comes out the lifters, rockers and bearings? I would have thought less, but maybe it makes sense. In any case, the air coming out of the 1.5" filler hole was enough to feel on your face.
Last edited by Blacksix; Mar 19, 2023 at 08:00 PM.
Thread Starter
On The Tree
Joined: Mar 2007
Posts: 113
Likes: 14
From: Calgary, AB
Any other thoughts on how oil pressure can be lost between the the filter and the top end? Leaky barbell seal? It'd have to be pouring out of there. Or, are the mains actually bad? Grasping at all straws here before pulling the motor.
Thread Starter
On The Tree
Joined: Mar 2007
Posts: 113
Likes: 14
From: Calgary, AB
So I've removed the pan and double-checked the o-ring, it was perfect but put in a new one. While I was in there I rechecked a couple of bearings, they're fine with around 0.0015 clearance. Removed the transmission, replaced the barbell and rear cover gasket, still have 5psi oil pressure.
Everything has now been checked from pump back to pan: o-ring, tried different filters, barbell, rear cover seal, no screen at the gauge, AFM tower blockoffs, cam retainer plate, front plug in place, bearing clearances OK. What could possibly be left? The lifters are a mix of used lifters that I checked for operation and made sure they slid nice in the bores. Is there any chance of losing oil pressure from bad lifters? I don't see how.
Everything has now been checked from pump back to pan: o-ring, tried different filters, barbell, rear cover seal, no screen at the gauge, AFM tower blockoffs, cam retainer plate, front plug in place, bearing clearances OK. What could possibly be left? The lifters are a mix of used lifters that I checked for operation and made sure they slid nice in the bores. Is there any chance of losing oil pressure from bad lifters? I don't see how.