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What oil pump to replace high-volume pump in "recent" rebuild?

11K views 67 replies 11 participants last post by  Ken Hennessy 
#1 ·
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.php?pk=8309848&cc=1049701

And a Sealed Power:
https://www.rockauto.com/en/moreinfo.php?pk=207958&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?
 
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#2 · (Edited)
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
 
#3 ·
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.

Mark: Snowman-33
 
#4 ·
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
 
#5 ·
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
 
#6 ·
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?
 
#7 ·
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.
 
#8 ·
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.
 
#9 ·
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
Cola forged crank shaft 3.875 stroke
Oliver Billet 6.0 rods
Oliver Billet mains
JE flat top pistons
LE ported TF 23 degree 215cc heads with the big 2.08 intake valve
 
#10 ·
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.
 
#11 ·
Flesh

whatever oil pump you do get, but a metal oil pump drive shaft. ARP, Mellig, etc make them for around $10

stock shaft has a plastic collar which when aged can crack on re-install which if it breaks (read it will) the motor goes boom very fast unless you catch the OP gauge pegged at zero soon enough
 
#12 ·
So, if high volume / pressure pumps typically come with the HV / P spring installed, could I theoretically just need to swap back into the standard volume / pressure spring and be "okay"?

If yes, but I don't know what pump is currently installed, how do I know what spring to use? Is the SV / P spring for all Melling pumps for SBC motors the same, for example? (Assuming my car has a Melling pump--I have no idea what the builder installed.)
 
#13 ·
I kind of have that same question. I bought the Melling Std volume, std pressure pump, and it came with the piece of paper stating that it was pre-installed with a high pressure spring, and included the std. pressure spring if I want to swap.

In theory the pressure spring just regulates the bypass within the pump itself, and really shouldn't have any effect on volume. I think (but don't quote me) the high pressure spring is pink, and the std pressure is yellow.
 
#15 ·
I'm trying to decide between these two Melling pumps:

Melling Oil Pumps M155 - $40.46
https://www.summitracing.com/parts/mel-m155

(It recommends this: Melling Heavy-Duty Intermediate Driveshafts IS-55E - $9.37
https://www.summitracing.com/parts/mel-is-55e/overview/)

Melling Performance Oil Pumps 10554 - $96.45
https://www.summitracing.com/parts/mel-10554/overview/

I'll need this: Pioneer Oil Pump Pickup Tube Retainers 839061 - $18.99
https://www.summitracing.com/parts/pio-839061

Can I use the existing pickup? If not, what do I need?

Anything else I'll need, hardware-wise, aside from an oil pan gasket, oil, and an oil filter?
 
#16 ·
I have the Melling M155 in my ERE383. The oil pressure on cold startup is around 50psi and goes down to 25 when hot. At cruising speeds(70mph) the oil pressure is ~42. WOT the pressure is ~70.

After a 20 minute lapping session on a road course(95 degree outside temperature) the oil pressure is ~20psi. I run 10W30 full synthetic oil without the external oil cooler and a larger WIX 51060 oil filter.

YMMV
 
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#17 ·
I figure I should touch base on a baffled / windage oil pan as suggested elsewhere in this thread. What I've noticed with oil pressure is this:

--when accelerating moderately, even when holding a gear manually, oil pressure seems to climb progressively with RPM and does not drop off
--the same thing happens if I accelerate moderlately / lightly all the way to redline using the transmission to hold a gear, and it usually peaks around 70 PSI with the engine warm
--when accelerating aggressively (like if I'm cruising along and then dip into the throttle pretty deep and cause the trans to downshift to second), oil pressure will seem to jump to ~70 PSI, then drop to just under ~55 PSI and hold there all the way to redline

I detailed this stuff in another thread, but of course can't find it at the moment.

Is this possibly / likely to be something that a windage oil pan would solve? It seems like now (while replacing the oil pump) would be the time to address this.
 
#19 ·
Flesh
are you saying you don't have a windage tray now?
the stock one is fine if yours is missing and should be installed
As far as I know, my LT1 has a stock oil pan. So.. that's sufficient? Is there anything that I should have the shop check for when they have the pan off to replace the oil pump?
 
#20 ·
#22 ·
You guys have any input on the oil pressure behavior shown in the videos in that thread? Where the oil pressure drops by about 15 psi under initial acceleration, but eventually starts acting normally and raises in accordance with the RPM? Just figure I'll see if there are any more opinions before I order the oil pump and schedule the installation.

Heck, I'll link the videos here for ease of viewing.



 
#23 ·
Flesh

I assume when your motor was rebuilt with a HV pump because the bearing clearances were set up slightly wider. I have my motor that way. Hot idle OP is 45-47 and climbs to 60 ish at WOT. This is a Autometer gauge. Cold OP at idle is 55 and would likely peg at 100 if I stayed in it when engine is cold but I don't do that

Your dash gauge "may" not be accurate in terms of PSI. You would need to plumb in a 2nd mechanical gauge to compare though

I noted in my last post that if the windage tray was not put back in that can cause OP problems as the crank will foam the oil at high RPM which will drop pressure.

or if oil pick up came off that will cause OP to drop on hard launch or turns

The drop then recover may be just the bypass valve of the pump activating. Can't remember what PSI they would do that but 70 may be it

Might want to confirm OP using another gauge and also confirm you have a windage tray. Removing the oil level sensor you should be able to see it or feel it with a screw driver. Of course one of those snorkel USB cams plugged into your phone will give you a great view. If using a snorkel cam you could just go through the drain plug
 
#25 · (Edited)
The drop then recover may be just the bypass valve of the pump activating. Can't remember what PSI they would do that but 70 may be it

Might want to confirm OP using another gauge and also confirm you have a windage tray. Removing the oil level sensor you should be able to see it or feel it with a screw driver. Of course one of those snorkel USB cams plugged into your phone will give you a great view. If using a snorkel cam you could just go through the drain plug
I don't think it's the bypass activating causing the initial drop in oil pressure, because once the car hits second gear, the oil pressure climbs with RPM to almost 80 PSI. This in contrast to first gear where it climbs, then drops and stays a bit low until the next gear. My gut feeling is that something is causing not enough oil to be available at the pump, which is causing the brief initial pressure drop. And I suspect that the pressure drop is what's causing my higher-than-expected wear metals in UOAs.

The snorkel cam is a great idea! I used to have one but misplacecd it (read--pretty sure I loaned it out and didn't get it back) so time to get another one. Is there anything else that I should look for while in there? Like, would it be easy to tell if the pickup has fallen off or if the pickup height is wrong, etc?
 
#24 ·
In the videos - 70 - 80 PSI on a hot engine? That would worry me as much as oil pressure thats too low. The bypass kicks in at 70 and after that, nothing is being filtered.

The falling pressure could be a lot of different things but the first thing that comes to mind is cavitation. Maybe the pickup wasn't set correctly between the pan and the pickup and on hard accel the pump has a harder time getting oil through a too-constricted space. It's all just guessing though. No way to tell from this side of the screen
 
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#28 ·
I've had the sender changed and the resistor added so that the dash gauge is "real". Please, pretty please with sugar on top, for the sake of this discussion, let's assume that what the gauge shows is representative of what's actually happening in the engine. I am not going to hook up a separate oil pressure gauge or do anything else that second guesses the stock gauge unless I have the oil pump changed out and the issue still persists. Then you guys can laugh and tell me "I told you so", but I'll bet <imaginary sum of money> that it doesn't happen.
 
#29 ·
I've had the sender changed and the resistor added so that the dash gauge is "real". Please, pretty please with sugar on top, for the sake of this discussion, let's assume that what the gauge shows is representative of what's actually happening in the engine. .
ooooooK….

I take it by your post you had someone install a different sender and solder in a resistor vs you doing it.....and knowing it was done right.

oil pumps themselves are very simple devices that on their own rarely fail other than the pick up falling off or the stock plastic top of the OP drive assembly (under intake manifold) is cracked which allows the drive gear to "lift" away from the oil pump shaft which would cause a momentary drop in OP

The snorkel cam will show quickly if the PU fell off and also if you have a windage tray unless "you" rebuilt the motor, or have had the pan off to see, and know it was re-installed

The OP dropping on acceleration at upper rpm suggests, again assuming the gauge is correct, the pick up is off or clogged (that not likely unless the builder used stupid amounts of RTV on the pan gasket that are now granules clogging pick up screen) or the windage tray is missing and oil is cavitating (foaming) from crank spinning

My $.02 is get a snorkel cam and take a peek first before having someone, or yourself, swapping out a oil pump
 
#30 · (Edited)
So I drained the oil and jammed a snorkel cam up the drain plug hole. See below for a bunch of upside-down and hard-to-decipher pictures, that hopefully some of you will find helpful. It appears that there is a baffle. It also appears that the oil pump has 155HV on it and some character before it which might be an M, which as far as I can tell is a Ultra-Power M155HV high-volume oil pump. https://www.rockauto.com/en/moreinf...L3grHQKK7X6H6VgU7xn7cpDgSESl2x2PWay2QKkHTW7A=

Or maybe it is a Melling-brand pump. Not sure why the one on RockAuto says it's "Ultra-Power", if Melling clearly sells a pump with part number M155HV. https://www.amazon.com/Melling-M155HV-Oil-Pump/dp/B000C4KIYM

The car is up on ramps, hence why the oil looks like it's pooling towards one side of the pickup.

If the baffle is there and the pickup hasn't fallen off, then there doesn't seem to be anything obvious wrong "externally". But if I get better wear numbers from 0W20 than I do from 0W30 or 0W40, could it be that that the high-volume oil pump is sucking the pan dry under hard acceleration, and that's where the elevated levels of wear metals are coming from?

If that's the case, could a bandaid fix be to add extra oil? Normally it takes 5 quarts to get to the top of the fill line with an oil and filter change. Maybe go with 6 or even 7 quarts? Or should I just stick with the original plan of having a standard volume and standard pressure oil pump installed?













 
#37 ·
If the baffle is there and the pickup hasn't fallen off, then there doesn't seem to be anything obvious wrong "externally". But if I get better wear numbers from 0W20 than I do from 0W30 or 0W40, could it be that that the high-volume oil pump is sucking the pan dry under hard acceleration, and that's where the elevated levels of wear metals are coming from?

If that's the case, could a bandaid fix be to add extra oil? Normally it takes 5 quarts to get to the top of the fill line with an oil and filter change. Maybe go with 6 or even 7 quarts? Or should I just stick with the original plan of having a standard volume and standard pressure oil pump installed?
so if I understand right you have this fluctuating OP issue and have not so great oil analysis results, right?

In the one pic showing what looks to be the pump pick up it appears to be about 1/4" above the pan bottom which should be fine. Hard to tell by the pic though

HV pumps should be used "IF" the bearing clearances are set up slightly wider than stock...not with motors using stock bearing clearances.

Was your motor built with wider bearing clearances?

If your bearing clearances are wider than you should not be using 0-20 or 0-30 or 0 anything oil. Use 20-50. Once a HV, or any pump, hits its bypass pressure the oil just goes back into the pan. A HV pump will not suck a pan dry, period.

I have a 155HV with a press in pick up that is brazed on running a stock pan. No issues in 40k mi.

Is your oil analysis from Blackstone?

Was the sample taken from hot oil mid way through the drain? (answer needs to be yes)

You can try a 6qt fill to see if the fluctuating OP issues goes away but you should not have to run 6 qts "because" you have a HV pump.

Have you checked the OP drive gear in the lifter valley?

If the top part (plastic) is cracked or broken that gear will "lift" up making the gears slip (grind and leave crap in oil which would show up on analysis)
 
#31 · (Edited)
I did some Googling for M155HV and I found this thread:
https://www.hotrodders.com/forum/melling-m155hv-oil-pump-135504.html

In it, one of the posters says:
The M155HV pump has longer spur gears for "high volume" which makes the housing 0.587" longer. Therefore you must use a deeper pan and an aftermarket longer pick-up screen assembly. You cannot use a Chevy high volume oil pump in a stock oil pan. That is because the stock oil pump pick-up assembly is as short as it can get due to the location of the oil pump.
Also this:
The correct numbers for the Melling pump that uses a 3/4" pick up tube is M155HV (high volume) and M155 (std. volume). Just because a pump has an inlet for a 3/4" pick up tube does not necessarily mean it is a "high volume pump". The length of the spur gears and pump housing determines wheather it is a high volume pump or not, not the size of the pick up tube.

A Melling M155 pump is likely what you have in your oil pan because those use a 3/4" pick up tube and they will fit a stock oil pan with from 0.375" to 0.500" clearance from the floor of the pan. The Melling M155HV pump will have from 0.000" to 0.200" clearnce from the bottom of the oil pan.

A 5 year old child with knowlede of basic math can see that at a glance. It has been substantiated that the Melling M155HV high volume pump is at least 0.300" longer than a M155 standard volume pump. The M155HV pump fit my 9.250" deep oil pan with less than 0.200" clearance..or less than 1/4" .

Maybe you have one of those rare "adjustable" oil pump pick ups. LOL Adjustable with a 5 lb. hammer.
My LT1 still clearly has the stock oil pan so.. is the M155HV too "tall" and causing problems because of that?
 
#32 ·
What problem are you trying to solve here?

I can't think of any possible downside to a high volume oil pump except that it takes a little bit more power to run it.

I watched the videos and don't see anything abnormal there - the bypass relief is set to about 60 psi (on the gauge), it has about a 15-20 psi rise over the set point as the flow increases due to RPM, there's a bit of overshoot as it goes from closed to open which, in my opinion is what causes the pressure spike to ~75 psi and then the "dip" back to ~60 psi then continue it's similar walk back up to ~75 psi as the RPM's climb.

When you accelerate the engine quickly, the flow from the oil pump increases quickly and it can't all go out the bearings and such within the engine. The relief valve overshoots a bit (normal) until it can open far enough to let all the oil pass, but it opens a bit too far so then undershoots (also normal) while it closes and then finally stabilizes out and maintains 60-75 psi oil pressure as the engine RPM's stay high.

Does any/all of this sound plausible?
 
#33 ·
The problem I'm trying to resolve is that the wear metal numbers from UOAs are a lot higher than they should be.
 
#34 ·
Ok - Reading your other thread, the motor has (a year ago) 12k miles on the rebuild? There are many things that will cause elevated iron and chromium levels.

Like I mentioned above (and BALLSS mentioned in both threads), there does not appear to be anything abnormal with your oil pressure or anything that would correlate to increased levels on iron and chromium.

Just a few questions about the oil analysis to help get up to speed on what is going on...

1) What lab is doing the analysis?
2) How many analyses have been performed and at what miles on the engine
3) What oil filter are you running?
4) Do the analyses have particle counts? Would you be able to post the analyses?

And just to dispel one myth/rumor...

atlantadan said:
..........The bypass kicks in at 70 and after that, nothing is being filtered...........
The same amount of oil is being filtered with the bypass open as closed (as much as the engine will take). The extra oil going out the bypass is not being filtered, but that is of little concern since the oil pump is the only thing it has gone through. No oil goes to the engine without being filtered (in warm operating conditions).
 
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