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Unread 05-15-2013, 09:55 PM   #1
rosco3059
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Oil pressure question

Hi all,

My 81 CJ7 4.2 I6 has been having some oil pressure issues. Upon start up, I am getting about 25 PSI and lose all the pressure after I begin driving. Anybody have a similar problem? I am contemplating replacing the oil pressure gauge but have not done so yet. Also of note is that I replaced the oil pump recently. However, I don't think I would get any pressure if was not primed properly. I have also not noticed any ticking or knocking in the motor.

John

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Unread 05-16-2013, 02:12 AM   #2
keith460
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Did you use a gasket between the oil pump and engine block mounting surface? Depending on the mating surfaces of both, sometimes you need a gasket and sometimes not. I had a similar problem last year on my I6 engine where pressure was good when engine was cold but dropped significantly once it warmed up. Dropped the pan and found I forgot to put in a gasket for the new oil pump but the original never had one that I recall. Anyway, once the gasket was in place, oil pressure stays the same whether its a cold or hot engine and I have about 20psi at idle and up to 70psi on the high.

A good feature is to add an additional Oil Pressure Gauge right at the engine block so you know what kind of pressure you have at a glance. I bought a small glycerin filled gauge from McMaster-Carr.com. The one in the photo is not liquid filled and was shortly changed out with one that is.

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Unread 05-16-2013, 05:24 AM   #3
Matt1981CJ7
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You may consider checking the tolerance between the pump gears and the pressure plate. Over time, the gears and plate will wear causing a drop in pressure.

Also, make sure the relief valve slides freely inside the housing.

Good luck,

Matt
oilpump1.jpg   oilpump4.jpg   oilpump3.jpg   oilpump2.jpg  
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Unread 05-16-2013, 09:20 AM   #4
rosco3059
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Excellent suggestions gents! I will check these two potential problems out.
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Unread 05-16-2013, 07:08 PM   #5
rosco3059
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Quote:
Originally Posted by keith460
Did you use a gasket between the oil pump and engine block mounting surface? Depending on the mating surfaces of both, sometimes you need a gasket and sometimes not. I had a similar problem last year on my I6 engine where pressure was good when engine was cold but dropped significantly once it warmed up. Dropped the pan and found I forgot to put in a gasket for the new oil pump but the original never had one that I recall. Anyway, once the gasket was in place, oil pressure stays the same whether its a cold or hot engine and I have about 20psi at idle and up to 70psi on the high.

A good feature is to add an additional Oil Pressure Gauge right at the engine block so you know what kind of pressure you have at a glance. I bought a small glycerin filled gauge from McMaster-Carr.com. The one in the photo is not liquid filled and was shortly changed out with one that is.
Keith,

Where did you attach?
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Unread 05-16-2013, 07:44 PM   #6
keith460
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Attach what? The pressure gauge?

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Unread 05-16-2013, 08:22 PM   #7
rosco3059
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Quote:
Originally Posted by keith460
Attach what? The pressure gauge?

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Yes, the pressure gauge
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Unread 05-16-2013, 08:28 PM   #8
keith460
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I had to remove the pipe fitting and drill and tap another 1/8 NPT for the gauge.

Used the existing pipe fitting as a pilot hole guide for centering while drilling. Then flipped the block around and finished drilling with the correct size drill for taping the 1/8" NPT.


Then tapped it to a 1/8" NPT.


Installed back in the engine block.
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