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Old 03-01-2009, 04:10 PM
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Low oil pressure...

I have a 67 c10 with a 355sb. I am having problems with the oil pressure dropping to around 20 after truck warms up and is driven for a couple miles. When I get the rpms up the oil pressure comes up to 40 to 45. Truck starts out on a cold engine just over 50. Does anyone have any ideas why this is happening? If I need to provide more info please let me know and I will do my best.

Engine and 400t tranny both have about 450 miles on them.

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Old 03-01-2009, 04:28 PM
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Who rebuilt it? How long ago? Sounds like possible main bearings are worn out.. When warm does it start tapping some? The mains might be down to the copper causing weak oil pressure ..If its a fresh build how was the mains installed?
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Old 03-01-2009, 04:47 PM
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Quote:
Originally Posted by Davi☠Rotten
Who rebuilt it? How long ago? Sounds like possible main bearings are worn out.. When warm does it start tapping some? The mains might be down to the copper causing weak oil pressure ..If its a fresh build how was the mains installed?
They guy i bought if from on Jan 1, 2009 said engine and tranny both had just under 100 miles on them. so I would assume it was done pretty recently. Unfortunately this means I have no clue how the mains was installed.

The engine runs like a champ, nothing sound or feels wierd at anytime whether it is idling or I am putting the hammer down.

I have noticed that there seems to be a very small oil leak, as I now have a couple spots on my garage floor about the size of a nickle. I have now idea were that is coming from either...
At this time tho I am not really concerned about the small oil leak, as it is extremely small. but the oil pressure does bother me.
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Old 03-01-2009, 04:55 PM
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I wouldnt be to worried about it.20 lbs after warm up not really to bad you said it goes up when rpm go up.i take the 20 lbs is at idle.is it 40 to 45 when driving .when sitting still if you rev the engine does it climb higher then 45. cole

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Old 03-01-2009, 05:04 PM
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here something you can read from here.maybe it will help. Small Block Chevy Oil Pressure cole
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Old 03-01-2009, 05:10 PM
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you got it, gets as low as 20 when idling and gets back up to 40-45 when giving it some rpms. when at idle and i rev it doesnt quite come all the way up to 40 but right there pretty close to it...
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Old 03-01-2009, 05:18 PM
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I dont think you have anything to worry about. but i would keep a eye on things its not making any noises. it would be nice to know what brand bearings are in the bottom end and what oil pump was installed when it was built. cole
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Old 03-01-2009, 05:34 PM
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Sounds pretty normal to me... if you are concerned go with a heavier weight oil, maybe a 10w-40 instead of the typical 10w-30. Just to make sure there's no knocking at any point in time right?
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Old 03-01-2009, 05:37 PM
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Sounds pretty good to me too.
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Old 03-01-2009, 06:17 PM
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Quote:
Originally Posted by GenYnNC
Sounds pretty normal to me... if you are concerned go with a heavier weight oil, maybe a 10w-40 instead of the typical 10w-30. Just to make sure there's no knocking at any point in time right?
thats right. no knocking, it just got me worried when i saw the oil pressure dropping the way it has been.
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Old 03-01-2009, 06:32 PM
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sounds to me like the oil filter isnt on right. i had the same problems and when i changed the oil i noitced that the filter wasnt on tight enough. that could be why its leaking too. not a big deal though.
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Old 03-01-2009, 06:57 PM
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Quote:
Originally Posted by brad1
thats right. no knocking, it just got me worried when i saw the oil pressure dropping the way it has been.
my 57 drops to 10 after romping for a while .
it's bored .060 and the stock radiator still .
it gets hot and won't cool down unless you turn it off .
after a hour , 40 psi again on oil .
i use that lucas in mine and 20 -50 oil .
been romping since 1979 and still going strong .
maybe your running little on hot side .
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Old 03-02-2009, 11:15 AM
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Sounds normal. With a standard pressure pump, pressure gets kinda low at idle at temperature.

I'm running a SBC .030 over, fresh clevite bearings all around, running 0W30. Once the block comes up to temp, it's a combination of the pump pressure and the viscosity that causes a low pressure condition.

I have a low pressure warning light (autometer 3-way warning system) that triggers below 25psi, and it frequently comes on at idle after the block is at temp.

Another thing you might check is the sender unit or the mechanical line tap that's feeding your gauge, make sure it's reading accurately.

the blonde weasel
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Old 03-02-2009, 12:00 PM
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brad,
"where" the sender is mounted on the oil galleys is likely the cause for what you are seeing....

your reading the "remaining" pressure after the pressure drop from bleeding oil at the main and cam bearings...

you have 20psi left going thru the pushrods to the rockers at idle and that's more than plenty when the motor is warmed up....

the pressure climbs with rpms because the pump gpm increase exceeds the basically constant bearings bleed gpm rate...
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Old 03-02-2009, 02:18 PM
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Cool, thanks to everyone for the good feedback. I am happy to know that this is a common occurance and not something I should fret about. I will let yall know if something changes.

Thanks Again
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