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Discussion Starter #1
i wanted to ask, if your oil pressure gauge is steady at idle around 40 psi and then all of a sudden it rapidly goes down to 30 psi and rapidly goes back to 40 psi with no RPM change, and does this once in a while, does it mean your main bearings are in trouble?
 

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i wanted to ask, if your oil pressure gauge is steady at idle around 40 psi and then all of a sudden it rapidly goes down to 30 psi and rapidly goes back to 40 psi with no RPM change, and does this once in a while, does it mean your main bearings are in trouble?

posibly! have you tryed another gauge just to make sure that isnt your prob? i always like to start with the easiest posible solution and work towards the worst. JMO.
 

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i have not tried another gauge yet. but i should. now what if i try another guage and it does it with that gauge too?
a GM shop stuart mechanic told me in the past that theory is that when mains go the guage flucuates like that...so i was wondering if its 100% true...but my guage has done that a couple time when the engine was fully hot...
 

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Any chance your pick up is sucking air?
 

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Any chance your pick up is sucking air?
well the dipstick shows the oil level to be right in the middle of the xxxx lines. so i dont think it is but then again im not able to see in the oil pan...anyway to test it somehow for it picking up air?
 

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Just an uneducated guess, but I would think (like was previously mentioned) that if it is jumping around that quickly on the gage it may have the pump exposed to air. Maybe the pick up fell off?


The way that I usually check for main bearing "leaks" caused by wear or excessive clearance is to drive the vehicle on the highway with the oil hot and hold a steady RPM at say 55 mph in high gear. At that speed say you have 50lbs of oil pressure, now if you put the petal to the floor in the same trans gear the engine will see a major increase in load with little increase in engine speed. This increase in load will try and "push" the crankshaft into the lower main brg and possibly expose more of an aperature on the upper main brg.. Typically a normal Chev main is only grooved on the upper half. and if the clearance is excessive this will allow a major loss of oil and generally a rapid decrease in oil pressure. If you let off of the accelerator the pressure will return.

If this test (with hot oil) does not show a drop in pressure (assuming you have an accurate and properly plumbed gage) I usually think the mains are not a source of pressure drop.


Thats just my test, so dont thinks accurate but its typically held true for me.


Good luck

Jeff
 

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Will the above test tell you anything about the rod bearings or just the mains?
 

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In my opinion it will generally only show typical main brg clearance. The condition is really another issue?

The mains may be new and/or in great shape as well as the crank itself, but for whatever reason there is excessive clearance between the crank and brg..


Jeff
 
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