Oil pressure

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Ignatios

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Hello all
You wonderful people helped me in the past and I’m coming back for some more if you would be generous and help me out with your expertise.
Ok, 2000 mercruiser 350 mag vortec converted from mpi to carb, this problem been around even before o converted to carb.
The problem is that when I start my engine oil pressure is about 80ish but after driving it for about an hour it drops to zero at idle but if I give it a little gas it goes up to 40 and if I drive it for more than 2 hours it only go up to about 20 when I ruv it up but drops to zero when idling any thoughts or suggestion would be greatly appreciated and God bless.
Nick
 
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dubs283

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When you did the fuel/ignition swap did you install/connect the audio warning system, specifically the oil pressure switch?
 
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tank1949

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Ignatios said:
Hello all
You wonderful people helped me in the past and I’m coming back for some more if you would be generous and help me out with your expertise.
Ok, 2000 mercruiser 350 mag vortec converted from mpi to carb, this problem been around even before o converted to carb.
The problem is that when I start my engine oil pressure is about 80ish but after driving it for about an hour it drops to zero at idle but if I give it a little gas it goes up to 40 and if I drive it for more than 2 hours it only go up to about 20 when I ruv it up but drops to zero when idling any thoughts or suggestion would be greatly appreciated and God bless.
Nick
Click to expand...
add an oil pressure gauge manually back at engine.
 
Scott06

Scott06

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as others have mentioned verify with a mechanical gauge. If oil pressure is accurate you can try 50 wt , otherwise engine needs teardown
 
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Ignatios

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I’m
ROY WILLIAMS said:
the crankshaft bearings worn out ....inspect the engine oil of the ?
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can you please explain to me though if the bearings are worn shouldn’t the oil pressure be down at all time? And why would it go up to 40 as I give it a little gaz? Thank you
 
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Ignatios

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Scott06 said:
as others have mentioned verify with a mechanical gauge. If oil pressure is accurate you can try 50 wt , otherwise engine needs teardown
Click to expand...
Do you mean by accurate that if the mechanical gauge shows different then what the gauge at the dashboard is showing? Then I should put 50 wt ?
Tearing down the engine to do what? An overhaul? Or replacing certain part? Thank you.
 
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tank1949

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Ignatios said:
Do you mean by accurate that if the mechanical gauge shows different then what the gauge at the dashboard is showing? Then I should put 50 wt ?
Tearing down the engine to do what? An overhaul? Or replacing certain part? Thank you.
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If mechanical shows constant oil pressure in tune with normal readings as engine warms, then something else is defective in your other gauge or wiring. Pray you don't need a motor tear down and new bearings.
 
Scott06

Scott06

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Ignatios said:
Do you mean by accurate that if the mechanical gauge shows different then what the gauge at the dashboard is showing? Then I should put 50 wt ?
Tearing down the engine to do what? An overhaul? Or replacing certain part? Thank you.
Click to expand...
I mean if a mechanical gauge matches what the electrical gauge in boat shows. This would confirm you have low oil pressure vs a bad gauge or sender. If the mechanical gauge reads higher the engine is mechanically ok.

low oil pressure is from excessive bearing clearances and wear and or oil pump Issues. You need about 10 psi of oil pressure hot per 1000 rpm of engine pressure for the engine to keep living. if you have excessive bearing clearances you may be able to run heavier oil to band aid it. Can try 50 wt maybe add something like lucas oil treatment that thickens the oil.

if the oil pressure is too low yes you need to pull the engine to verify main and rod bearing clearances and check the oil pump. If the clearances are too big or out of round you need to have a machine shop remachine the crank and rods , then basically you are into an engine rebuild.possible you could have a bad oil pump or clogged oil pump intake screen. Either way is indicative of lack of maintenance.
do you have fuel diluting the oil ? Have you changed the oil?
either way you can buy a cheap mechanical gauge at the autoparts store, put it on and hope you have a boat gauge issue .start by verifying what you have pressure wise
 
Lou C

Lou C

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I would try the mechanical gauge and see what it shows you.
The lowest I have ever seen my oil pressure go on my old 1988 4.3 (original block/rotating assembly, reman heads in 2017) is about 20-25 psi at a 600 rpm idle speed, this is after coming off plane. Slow running at or slightly above idle gives about 40 psi, up on plane at 3500 rpm gives about 55-60.
25/40 Quicksilver oil. Just switched to Quicksilver syn blend 25/50, don't expect much difference though.
 
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Ignatios

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tank1949 said:
If mechanical shows constant oil pressure in tune with normal readings as engine warms, then something else is defective in your other gauge or wiring. Pray you don't need a motor tear down and new bearings.
Click to expand...
Got it thank you very much, prayers always helped in my case I’ll do that too :)
 
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Ignatios

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Scott06 said:
I mean if a mechanical gauge matches what the electrical gauge in boat shows. This would confirm you have low oil pressure vs a bad gauge or sender. If the mechanical gauge reads higher the engine is mechanically ok.

low oil pressure is from excessive bearing clearances and wear and or oil pump Issues. You need about 10 psi of oil pressure hot per 1000 rpm of engine pressure for the engine to keep living. if you have excessive bearing clearances you may be able to run heavier oil to band aid it. Can try 50 wt maybe add something like lucas oil treatment that thickens the oil.

if the oil pressure is too low yes you need to pull the engine to verify main and rod bearing clearances and check the oil pump. If the clearances are too big or out of round you need to have a machine shop remachine the crank and rods , then basically you are into an engine rebuild.possible you could have a bad oil pump or clogged oil pump intake screen. Either way is indicative of lack of maintenance.
do you have fuel diluting the oil ? Have you changed the oil?
either way you can buy a cheap mechanical gauge at the autoparts store, put it on and hope you have a boat gauge issue .start by verifying what you have pressure wise
Click to expand...
Thank you very much for taking up the time to explain in details to … now I see what all that means and yes I added some additives to the engine so I’m hoping this is what it is.
 
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Ignatios

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Mar 15, 2015
Messages
115
Lou C said:
I would try the mechanical gauge and see what it shows you.
The lowest I have ever seen my oil pressure go on my old 1988 4.3 (original block/rotating assembly, reman heads in 2017) is about 20-25 psi at a 600 rpm idle speed, this is after coming off plane. Slow running at or slightly above idle gives about 40 psi, up on plane at 3500 rpm gives about 55-60.
25/40 Quicksilver oil. Just switched to Quicksilver syn blend 25/50, don't expect much difference though.
Click to expand...
See when I go it goes up to over 40 even if I give it a little gas it jumps up and it goes back down but in the morning it is as high as 70 or plus
 
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