Lower than normal oil pressure

Jb72

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Wisconsin
Have a 72 Pontiac with a 400. Question is last year at start up ran around 40 lbs and while driving 50-60. this year I notice start up is 20-30 which I believe is fine however after engine is warm its runs the bare minimum 4000 rpm with be just below or at 40 when it used to be 50-60 /2000 will be just below or at 2. Have mechanical oil gauge /run green oil 10w30/motor is 4 years old off rebuild first three years ran all the same. Is this a major cause for concern? Thanks
 

melsg5

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confirm the accuracy of the gauge with a temporary hook up of a hand held gauge.
have you switched to a different oil filter?
 

Jb72

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Wisconsin
confirm the accuracy of the gauge with a temporary hook up of a hand held gauge.
have you switched to a different oil filter?
Filter should be the same I don't believe I switched it (will have to try different gauge) upon start up gauge reads good after about 10 min that's when the pressure drops and runs the min. Thanks I'll try the gauge
 

melsg5

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you could also try a bottle of STP to see if it helps with the pressure
you did put 6 quarts of oil in the engine?
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cammerjeff

Member
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Belleville MI
40psi is plenty of oil pressure, but I would be concerned with the drop. As previously stated I would recheck it with another mechanical gauge to make sure the reading is good, then if the reading is confirmed I would check for leaks, and pull and cut apart the oil filter looking for brass shavings.
In my past experience a 10-20psi drop in oil pressure is the 1st sign of either a main or rod bearing starting to go. The increase in bearing clearance lets more oil escape decreasing the psi.
But don't assume its a bearing, it could also be something like an oil jornal plug coming loose causing an internal oil leak in the system, under the timing chain cover. This condition leaks the oil around the oil galley back into the oil pan. That is why I have the machine shop tap the oil galley ends, and install a pipe plug in them.
 

Jb72

New member
4
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Wisconsin
40psi is plenty of oil pressure, but I would be concerned with the drop. As previously stated I would recheck it with another mechanical gauge to make sure the reading is good, then if the reading is confirmed I would check for leaks, and pull and cut apart the oil filter looking for brass shavings.
In my past experience a 10-20psi drop in oil pressure is the 1st sign of either a main or rod bearing starting to go. The increase in bearing clearance lets more oil escape decreasing the psi.
But don't assume its a bearing, it could also be something like an oil jornal plug coming loose causing an internal oil leak in the system, under the timing chain cover. This condition leaks the oil around the oil galley back into the oil pan. That is why I have the machine shop tap the oil galley ends, and install a pipe plug in them.
Thanks for the info I will look into a different gauge when I get a chance
 

melsg5

Staff member
SUSTAINING MEMBER
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STP oil treatment, blue bottle, any auto parts store.
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