High Volume Oil Pump

So I recently changed the RMS and decided to change out the 30year old oil pump in my 91 4.0. I did not have a huge issue with it but figured it would be best to switch it out while I had everything opened up. I installed a high volume milling pump not knowing it was high volume. I became clear once I started it up and the oil pressure sat near 80 (cold idle) and later drops to about 50 on warm idle and runs about 65 on the highway.

To be honest my Jeep is running great but I do not know if the HV pump will cause issues... any thoughts on this? I bought the correct oil pump but I am hesitant to install it because everything is running great and well I really dont want to drop the oil pan again.

I have heard mixed information on it... like, its not going to hurt the engine because you just moving more oil and thats good... to you will washout your bearings..

need advice..

thanks
XJerod

I use a Melling high volume pump on my '90. I read up on this extensively and these pumps have a blow off valve so that they can't raise the pressure too high. Essentially, at a preset pressure level, the oil just dumps back into the pan so that it can't do any damage.



Mine has been working great for over 5 years. Having said this, my cold pressure sits at a little over 40 and holds there on the highway. After warming up it will drop to a little under 30 at idle.


I would recommend the High Volume pump but would not recommend the High Pressure version.

The big question would be, did you clearance the pan?

RCP Phx said:

The big question would be, did you clearance the pan?

Click to expand...

correct. And it takes alot of hammering!!

It's not that bad!

Had an sbc that did the same thing years ago never had a problem. I did put the high pressure pump in my last xj motor to try and prolong the bad bearings, raised initial cold pressure but hot idle was still flatlined.

My Melling pump fit just fine, I compared it to the old one and they were pretty much the same size. I had no issues getting it in and did not have to hammer at all.

Its just that my oil pressure is reading
70-80ish cold idle
35-50ish warm idle
65-highway warmed up
I have the new OEM pump but dont know if I should put it in because the engine runs and sounds great.

91 4.0
105k miles

It will bolt up , I didn't clearance my pan when I built my stroker. 6 months later I had to put a new set of main bearing in and clearance the pan!

Those pressures look fine. I recommend leaving it as is. I see no reason to worry about a 65psi cruise pressure. Bearing washout occurs when coolant contaminates the oil and changes its viscosity. As long as you don't have coolant contamination issues, take the increased pressures as a bonus.