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Unread 08-08-2010, 06:07 PM   #1
grimjeeperyj14
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Hi volume oil pump to help with low pressure problems.

Has anyone installed a hi volume oil pump in their 4.2 engine. I just rebuilt the whole engine including all new bearings,rings etc. and rebuilt the old oil pump. The oil presure still drops to about 5-20 psi when hot. Will a hi volume oil pump resolve this issue?

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Unread 08-08-2010, 06:26 PM   #2
jeeptim
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hi volume moves more oil it does not push it at a higher pressure
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Unread 08-08-2010, 06:28 PM   #3
Alabamaranger
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I rebuilt mine and I was low on money so I used the old oil pump. My pressure was about 5 at idle and 20 running down the road. Pull the pan and stuck a Hi performance pump and it fix my problem. It seems like it's 40 running down the road and 20+ at idle.

I would say try it. You got nothing to loose except the cost of the pump and time.
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Unread 08-08-2010, 06:53 PM   #4
Old4X
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When you set up your bearings, how much clearance did you set on your mains and rods?
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Unread 08-08-2010, 07:05 PM   #5
jdubsjeep
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back when I worked on motors in the 70-early 80's it was usually the camshaft bearings that dictated the loss of oil pressure. When people "rebuilt" their motors and didn't replace the camshaft bearings you would end up with that problem. Hi volume oil pump has nothing to do with that. It is basically an internal oil leak
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Unread 08-08-2010, 07:17 PM   #6
Alabamaranger
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I plastic gauge mine and it was within the specs. I only think old school folks do this. A lot of auto store places don't even know what plastic gauge or prussian blue for gear setup is.

Most high volume pumps also have a increase in pressure to help get the oil out to the bearings faster. If bearings have to much clearance, It may increase pressure a little to get it on up there a little higher.

As stated above, you might have a internal leak if your bearings have to much clearance. I believe the only way to find out is to try it. It would be impossible for us to tell you it will or will not work since we don't know the bearing clearances in your motor.

As a rule, most engines only need about 10 PSI of oil pressure for every 1,000 RPM of engine speed. Oil pressure will read higher than normal when a cold engine is first started because the oil is thick. Oil pressure will gradually drop as the engine warms up and the oil thins out. So normal oil pressure on a warm engine cruising down the highway is typically 30 PSI up to 45 PSI.
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Unread 08-08-2010, 07:48 PM   #7
jay-h
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A high volume pump for low oil pressure is likely treating the symptom more than the cause. If your pressure is low due to a poor pump, any replacement will help. If pressure is low due to bearings or similar issues, just bringing up the pressure is not addressing the problem (remember the bearings float on oil film, NOT pressure. The pressure is there to assure that the oil flow is adequate)
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Unread 08-09-2010, 04:25 PM   #8
grimjeeperyj14
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When I put the new bearings in I did not get oversized bearings. I simply used the standard size. I did not replace the cam bearings though.
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Unread 08-09-2010, 06:34 PM   #9
Old4X
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Quote:
Originally Posted by grimjeeperyj14 View Post
When I put the new bearings in I did not get oversized bearings. I simply used the standard size. I did not replace the cam bearings though.
Most likely problem is excess clearance on your bearings. Drop the pan and check at least 2 main and 2 rod bearings. Plastigauge costs less than 5 bucks these days and is enough to check every bearing in the engine several times. If clearance is excessive, install correct inserts to all that are out of spec.

Field maximum clearance is .003 IIRC, over that and you will show lower oil pressure.

No such animal as OVERSIZED bearing inserts, they are UNDERSIZED or STANDARD.
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Unread 08-09-2010, 07:06 PM   #10
laybackman
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Quote:
Originally Posted by grimjeeperyj14 View Post
When I put the new bearings in I did not get oversized bearings. I simply used the standard size. I did not replace the cam bearings though.
Putting in new rod and crank bearings but not Plastigaging them is not good. You have no idea what your clearances are. IF the clearances are all good that is called 'freshening up' a motor. It is not a rebuild.

Let us say that you had good clearance in the rods and main bearings (doubtful) BUT you have not replaced your worn cam bearings you are hemmoraging oil internally.

Putting in a high volume oil pump only increases the volume of oil you will hemmorage internally. The only proper fix for poor oil pressure is good bearing clearances.
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Unread 08-09-2010, 07:14 PM   #11
Larry93
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I installed a high volume oil pump from Melling in my 4.0. Cleared up the lifter noise I had ever since. Although I seem to need to replace my distributer gear every year now, little to much stress for the poor thing.

My pressure is way to hi now, 40 at idle and 60+ the rest. ( although it most likely is less than the gauge reading)


I also recall having to peen my oil pan on the side to clear the pumps larger body.
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Unread 08-09-2010, 08:55 PM   #12
laybackman
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Quote:
Originally Posted by Larry93 View Post
I installed a high volume oil pump from Melling in my 4.0. Cleared up the lifter noise I had ever since. Although I seem to need to replace my distributer gear every year now, little to much stress for the poor thing.

My pressure is way to hi now, 40 at idle and 60+ the rest. ( although it most likely is less than the gauge reading)


I also recall having to peen my oil pan on the side to clear the pumps larger body.
Your oil pressure is higher because your clearances are OK. Once the clearances get large oil pressure goes down because the space allows too much oil to bypass the original path it was designed to travel.
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