Which oil pump?

[mattbta]

2004 L59, 164k miles.

Idle oil pressure has been getting lower and lower, now around 30. When I was replacing the heads due to a crack, I did the o-ring again. One of the refurb heads cracked in less than 500 miles, so the top half is torn apart waiting on that to come in. I figure at this mileage might as well do the oil pump since i'm half way there anyways. Hoping that if I finally am not eating coolant in the oil and a new pump, fresh filter and oil, the pressure will return to 40+ hot idle. If not, might have a deeper problem.

So looking at Melling's options via their part finder:

Under "Stock" category

• M295 stock pressure, stock volume
• M295HV stock pressure, 18% higher volume, recommended for high mileage

Under "Performance" category

• 10295 10 PSI higher pressure
• 10296 10 PSI higher pressure, 18% higher volume

Or just go GM/Delco for completely stock? 12710303


I'd be inclined to go high pressure & volume, as at some point I may cam this thing, but ¯\_(ツ)_/¯

Thoughts?

 

[JonnyTahoe]

After watching a few vids on installing a new pump I decided to just leave the original pump alone. Balancer has to be pulled and pump has to be shimmed. You already have the motor apart this is the time to do the cam and lifters that's just common sense.

 

[mattbta]

Lifters were done when I replaced the heads the first time a few months back. I may have to watch some more vids as the GM Service Manual doesn't say anything about shimming the pump.

 

[JonnyTahoe]

Lifters were done when I replaced the heads the first time a few months back. I may have to watch some more vids as the GM Service Manual doesn't say anything about shimming the pump.

Your New pump(might as well get a Melling)will tell you in the installation instructions about the required shimming process. Look up Melling 295, 295HV oil pump Installation on YouTube. Find the video with the guy from melling installing a new pump on a new motor on a engine stand at the Melling Shop Headquarters.

 

[iamdub]

Chances are, the drop in oil pressure was caused by the bearings being worn due to the coolant thinning out the oil. Simply replacing the pump with an exact stock replacement isn't gonna repair this.

Pressure is a result of restriction to volume. Wider clearances (worn bearings) reduce the restriction so the oil pressure drops. You can either (A) tighten up the clearances by replacing the worn parts (new bearings, maybe new cam, etc.), or pump more volume through the existing clearances.

My experience: My brother's '05 5.3 kept dropping pressure until it was 0 and tapping something fierce. It was caused by coolant in the oil from a cracked head, causing sludge buildup that slowly choked off the pickup tube. Due to all the symptoms, there was obviously excess bearing wear. He wanted to get it going as cheaply as possible so we replaced the heads, oil pump, lifters, etc.- all the wear items except for bearings.

With a Melling M295HV and blue spring (the included lower pressure spring), the hot pressures stay in the 30s at idle, 40s when driving and high 70s at high RPM. I'm glad I used the lower pressure spring rather than leaving the red one installed.

 

[SouthernDuke]

When I did my 5.3 rebuild I went with the high flow high volume pump. That was a mistake. It runs to much pressure and i have blown the oil cooler block off plate off of my oil pan when I got into high rpm. Granted I had a fresh rebuild so everything was tight but my idle oil pressure is a little over 60 psi. At 4K it’s off scale high. Stock is fine. For your application I would say anything BUT the high flow/high pressure. You can any one but not both.