What oil pump to replace high-volume pump in "recent" rebuild? - Chevy Impala SS Forum
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post #1 of 44 (permalink) Old 04-23-2019, 03:50 AM Thread Starter
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What oil pump to replace high-volume pump in "recent" rebuild?

The "mechanic" who rebuilt the engine in my '94 wagon used a high-volume oil pump. On cold startup, even running synthetic 0W20, oil pressure is just under 80 psi. (Yes, I have an F-body cluster and yes I have the resistor mod and correct sensor so it shows actual oil pressure, and yes I realize that it's probably not completely accurate.) When accelerating hard, the gauge will jump, then immediately dip to below 60 psi, like the pump is bleeding off pressure or cavitating or something.

Wear metal numbers from 5K-mile oil changes have always been higher than I'd like--not terrible, but not good. The best numbers came from 0W20, the worst from 0W40--I feel like the high-volume pump needs the thinnest oil possible to not have flow issues. Some forum members have suggested switching back to a standard-volume oil pump, and I concur that it sounds like a good idea.

My current shop of choice (not the one that rebuilt the engine), said it would change out the oil pump for $300 in labor, plus parts.

For standard-volume oil pumps, Rockauto has a Melling:
https://www.rockauto.com/en/moreinfo...848&cc=1049701

And a Sealed Power:
https://www.rockauto.com/en/moreinfo...958&cc=1049701

There are two others but they specifically say "not for high performance or off road", so I'm gonna stay away from those.

Then, under the high-performance heading, Rockauto has literally about 20 different choices from Melling, all of which appear to be some variation of higher volume and / or higher pressure.

So, what oil pump do I want? What other parts will I need? Oil pan gasket, oil, and filter are obvious, but what else?

--'94 Caprice "SS" wagon, 0.30 over, high-volume oil pump, LT4 hot cam, 1.6:1 rockers, ported aluminum Corvette heads, shorty headers, PCM4Less tune, 4.10s, shift kit, side-exit dual exhaust with Flowmasters, OR X-pipe, F-body gauge cluster, Bonneville front and rear seats (working electrics), Bravada console shifter, Bilsteins, 12.7:1 Impala steering box, Boss 338s with 255/45R20s, bunch of other stuff I'm forgetting.
--'04 Mustang Cobra, '15 Audi S4
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post #2 of 44 (permalink) Old 04-23-2019, 05:19 AM
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I am running the Melling Shark Tooth 10% hv pump. Good unit and not terribly pricey. Also a good compromise between stock and higher volume. The part number is 10552 for the non Shark Tooth and 10552ST for the Shark Tooth. You can use the stock style pickup, but get the bolt-in variety. You will still have high pressure at start - I think mine is 70+. Once it warms up it drops down, but never really gets anywhere close to "low". The Melling stock volume / pressure is pressure is 10554 (I think) and that uses a press-in pickup.

The wear numbers in your UOI are interesting. If the front cam bearing was clocked incorrectly it allegedly can make for pressure issues and increased wear. Do you recall what the builder did? I have also seen where a builder used a stud that was a tick too long on the oil pump and when it was torqued down it put pressure on the backside of the bearing shell.

The dropoff on accel is due to the bypass valve in the filter. Once pressure gets too high, it opens up so bad things don't happen elsewhere


1995 Caprice ERE 383, CIA long tubes, Dynomax VT's, RAISS, Kore3/Z06 brakes, 3.42 posi, Boss 338 20's, 12 way seats, Impala SS console, etc etc etc

Last edited by atlantadan; 04-23-2019 at 05:23 AM.
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post #3 of 44 (permalink) Old 04-23-2019, 05:57 AM
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While gathering my parts for my engine I researched a long time on the pump. There were many articles pro/con on the high volume pumps. Some said that you needed a deeper pan to ovoid starving the engine while accelerating. I decided on the standard Melling, with the thicker base, and used this to secure the pickup to the pump. https://www.jegs.com/i/JEGS/555/23620/10002/-1 I chose this after checking the welding route. There was much on the yeah/nays here too. My engine is not assembled yet so I can't give you an informed opinion on it's performance.

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post #4 of 44 (permalink) Old 04-23-2019, 10:00 AM
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Flesh...do you know if your builder did slightly wider bearing clearances and chamfered the oil holes because of the HV pump?

That is why you would use one, If not than a standard volume pump would be better. You could run the high "pressure" spring in it (it is a different color spring than stock but I can't remember if it is the pink or white one)

My builder did slightly wider bearing clearances on my 383. Cold idle I am 55 PSI increasing to 70 ish with RPM but hot idle is 45 psi and 55-60 PSI at WOT rpm using the 10% HV Mellig. I have 35k mi on this motor. No "bearing hair" on drain plug when I do oil change and Blackstone test come back Steller. I even took a good look at my OP drive gear when I had intake off, perfect condition.

Many internet rumors...one being a HV pump sucks the oil pan dry. BS. You do need to run a windage tray though....or your crank will foam the oil and that's where you get oil pick up problems, especially in cornering and hard braking without a windage tray
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post #5 of 44 (permalink) Old 04-24-2019, 06:30 AM
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Whatever you do, get one with an bolt-on screen like the Mel-10552.
Or use a screen retainer like this one from jegs: https://www.jegs.com/i/JEGS/555/23620/10002/-1

The most common oil pump failure is simply when the pick-up falls off of the pump.

Nab
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post #6 of 44 (permalink) Old 04-26-2019, 01:51 PM
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I noticed that my standard volume Melling has a piece of paper stating that it is pre installed with the high pressure spring, and includes the standard pressure spring that can be swapped out. What is everyone's thoughts on high pressure vs. standard?


On that note...I always thought of pressure as a byproduct of restriction. Wouldn't you technically need higher volume in order to see higher pressures, all other things being the same? I know the springs on the oil pumps are for bleed off, but wouldn't a pump need to flow more oil in order to see increase pressures?

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post #7 of 44 (permalink) Old 04-26-2019, 02:18 PM
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FaSSt9602 - you have the right intuition - It depends on what the oil pressure is vs the spring setting. If the spring is set at 60 psi but the oil pump can only provide enough flow through the bearings to create 40 psi, it won't matter if you put an 80 psi spring in since there's only enough flow to generate 40 psi.
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post #8 of 44 (permalink) Old 04-30-2019, 12:26 PM
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Another point about oil pressure is that the reason it goes higher than the spring setting is because the bypass hole in the pump is too small for the pumps volume output.
The way to correct this is to drill the bypass hole larger.
For a stock build stay with factory pressure.

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post #9 of 44 (permalink) Old 05-01-2019, 10:04 AM
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Quote:
Originally Posted by z24 View Post
Another point about oil pressure is that the reason it goes higher than the spring setting is because the bypass hole in the pump is too small for the pumps volume output.
The way to correct this is to drill the bypass hole larger.
For a stock build stay with factory pressure.
My build is far from stock, and I'm torn between leaving the factory installed "high pressure" spring in place or tearing it apart to put in the "standard pressure" spring...

396 Forged rotating assembly
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post #10 of 44 (permalink) Old 05-01-2019, 10:27 AM
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I just checked - I have a Melling 10552 sitting on the shelf. Ran for about 3k miles. Zero problems and works perfectly. $100 shipped. I think I also have a Melling hardened steel drive-shaft for it that I'll throw in for $0.


1995 Caprice ERE 383, CIA long tubes, Dynomax VT's, RAISS, Kore3/Z06 brakes, 3.42 posi, Boss 338 20's, 12 way seats, Impala SS console, etc etc etc
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