1999 GMC Sierra 1500 oil pressure question

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Aug 4, 2021
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I have a 99 Sierra 1500 with a 2003 Silverado 4.3 engine. I took it on a regular off road trip and drove it kinda hard and after my oil pressure hasn’t been the same. I use to have 20psi when idling hot and in gear and about 55-60psi highway cruising. Used k&n with royal purple since I would get it very cheap but I wasn’t good with oil changes at the time. Horribly bad I know. But oil pressure went down and thought oh probably just need oil so I changed it and oil pressure hasn’t been the same. I have a aftermarket mechanical tube gauge on a A Pilar. I have a after market brass fitting that goes where the sending until would so no screen. And “change oil light” is always on even after changing oil. Changing oil raises pressure but only lasts a month before the Pressure goes to 0 at idle. I have a bad leak but with the lift kit I have cross member cannot be removed so no dropping the pan. I have to put a quart a week. During the week full of oil the pressure is fine. But after a month even being full of oil or making the oil thick I can’t get the pressure even to 20psi idling until I change the filter. Could there be a clog from not changing it when I wouldn’t change it? Or probably cam bearing? No lifter noise no knocking. The engine runs very very strong and has good compression. If that helps any. Also I’m new and young and don’t know a lot. Any opinions or suggestions would be greatly appreciated
 
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Have you had to add coolant? There was a run of 4.3 engines that would leak coolant from the intake gasket into the engine. Coolant will kill the bearings…
 
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That’s true the first run of the Vortec intake gaskets leaked at the front water ports into the cam valley which puts coolant right into the motor oil. Look inside the valve cover for a milky emulsion. I have an older version (pre Vortec) of the same engine and never had leaky intake gaskets. This 4.3 is in a boat and runs the Mercruiser marine oil 25/40. Oil pressure is 50-60 at speed and the lowest it gets is 20 psi at idle speed after running on plane for a while.
I did have water in the oil when the head gaskets leaked after an overheat but I got the water out fast & was able to save the short block & install reman cyl heads, new Fel/pro gaskets & ARP head gaskets. Still running well 5 years later.
I’m also wondering if you have crud/sludge blocking your oil intake screen…
PS do you have a remote oil filter set up? Could a delaminated hose be causing slow oil circulation? Kind of what can happen with brake hoses….
 

D60

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This ain't gonna help your problem but if you want to reset the OLI you have to turn key on and fully depress the skinny pedal three times. The vehicle isn't psychic and doesn't know you've changed the oil, it's merely basing predicted oil life on a fancy algorithm
 
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I am not sure if your vehicle has the same arrangement however this was removed from a newer Silverado on RP where the screen in front of the pressure sender was getting plugged. This was a chronic problem in this particular location.

Hopefully your issue will be easy to solve by changing a clogged screen.

Choose an oil with ester and or AN concentration and run 2,000 mile drains.

This is how I solved the problem in front of me and it has been great since.

Good Luck

David
 

D60

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Nov 6, 2017
Messages
1,576
Location
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I am not sure if your vehicle has the same arrangement however this was removed from a newer Silverado on RP where the screen in front of the pressure sender was getting plugged. This was a chronic problem in this particular location.

Hopefully your issue will be easy to solve by changing a clogged screen.

Choose an oil with ester and or AN concentration and run 2,000 mile drains.

This is how I solved the problem in front of me and it has been great since.

Good Luck

David
In Post #1:
"I have a after market brass fitting that goes where the sending until [sic] would so no screen."
 
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OP stated he’s got an oil leak and adds a quart a week. If he was sucking coolant in he’d have a dipstick milkshake every time he checked oil.
Or…since he does continuously add oil the detection of coolant isn’t as prevalent. It doesn’t take much. Had 200+ C1500 trucks with 4.3 in the fleet. Tough engine however coolant wrecks bearings quickly. Most times it was before the milkshake effect occurred. Very common to weep coolant from intake into lifter valley down to crankcase. Some never showed signs of low coolant prior to the bearings being wrecked. Just saying…
 

Jesseyourcalipers

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Before you tear into the engine, I would try another gauge and even flush the line of any debris between the engine and gauge.
This also came to mind. Because the gauge when I put it came with a plastic tube and it looks like clumps are in the line but my friend was like no that’s the oil. But it looks weird. I’m going to go rent a oil pressure tester and check directly.
 

Jesseyourcalipers

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That’s true the first run of the Vortec intake gaskets leaked at the front water ports into the cam valley which puts coolant right into the motor oil. Look inside the valve cover for a milky emulsion. I have an older version (pre Vortec) of the same engine and never had leaky intake gaskets. This 4.3 is in a boat and runs the Mercruiser marine oil 25/40. Oil pressure is 50-60 at speed and the lowest it gets is 20 psi at idle speed after running on plane for a while.
I did have water in the oil when the head gaskets leaked after an overheat but I got the water out fast & was able to save the short block & install reman cyl heads, new Fel/pro gaskets & ARP head gaskets. Still running well 5 years later.
I’m also wondering if you have crud/sludge blocking your oil intake screen…
PS do you have a remote oil filter set up? Could a delaminated hose be causing slow oil circulation? Kind of what can happen with brake hoses….
No brown oil and coolant never goes down. But that hose you speak of hmmm…….
 

Jesseyourcalipers

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Or…since he does continuously add oil the detection of coolant isn’t as prevalent. It doesn’t take much. Had 200+ C1500 trucks with 4.3 in the fleet. Tough engine however coolant wrecks bearings quickly. Most times it was before the milkshake effect occurred. Very common to weep coolant from intake into lifter valley down to crankcase. Some never showed signs of low coolant prior to the bearings being wrecked. Just saying…
Sometimes it’s not a quart a week. And my coolant has never gone down under the line I have painted on the max fill. And I have measured the oil coming out always exactly the 4.5 quarts. Unless it’s a table spoon of coolant that can blow my bearing. But I change oil once a month since the pressure doesn’t raise like I said after about a month. Can coolant even stay there long enough. Also running drinking water not coolant. Probably should’ve mentioned that. Havnt gotten around to putting coolant since I needed to warranty my aluminum radiator and I put a stock old radiator.
 
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No brown oil and coolant never goes down. But that hose you speak of hmmm…….
what made me think of it was that we had a problem with one of the brake hoses on my son's '17 Wrangler that caused a dragging brake, I thought it was a stuck caliper but it wasn't. The hose delaminated inside and wouldn't allow brake fluid to flow back to the master cyl.
I know that some of the S10 Blazers had a remote oil filter set up but I don't know if the full size trucks had that with the 4.3
GM's first run of gaskets on the Vortec (8 bolt intake) engines were bad. Also when replaced, the torque specs must be followed to the letter, they get much less torque than the old pre-Vortec models with the 12 bolt intake. (pre-Vortec was like 30-35 ft lbs, Vortec is like 11-15 or something like that).
 
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