Any truth to the myth that a HV oil pump can suck a pan dry? I have a fresh 355 Solid Roller. Idles at 40-50 PSI, drives around 55-60. When I mash the throttle my oil pressure begins to drop. I've just noticed this in the past month or so. I have a few theories. I'm hoping someone has seen or heard of this and can narrow things down.

1. HV oil pump sucking the pan dry.
2. Clogged oil return.

Any other possibilities? TIA

 

Pick-up tube fell off.

 

Faulty oil pump. Faulty filter.

 

if the pick up has fallen off, his idle pressures would suck. Any yes, a HV pump can suck a pan dry. Does your pressure drop as soon as you hit the throttle or does it not happen until the motor is wound up?

 

At idle the inlet on the pump will still be submerged.

 

Pressure begins to drop as soon as I stab the throttle. It usually cruises at around 55 or 60 PSI, but like I said, as soon as I stomp it, it steadily goes down. At 30 or 35 PSI, I lift, and then it goes back to normal. I'm running a standard 5 qt. pan (which I failed to mention in my original post.)

Comp Cams told me I need an oil restrictor kit, which I've bought, but I wanted some additional input, as the tranny has to come out in order to install this $13 kit.

The guy there thinks my oil pump is pumping oil to the upper end faster than it can drain back to the pan. Thanks for the responses, I really appreciate it.

 

Apeiron..........so if I'm understanding you correctly, you're validating five7kid's theory that the pick up tube has fallen off. Makes sense to me........at normal driving there's plenty of oil in the pan, so the pump is functioning somewhat minus the pickup tube, but under a heavy load, the pump is pumping more oil to the upper end, thus reducing oil in the pan, which in turn is starving the pump of oil since the pickup tube is off. It's going to my mechanic next week.........but it looks like I'll miss the Hot Rod Super Nationals this weekend. I have a ton of money in that motor, and don't want to risk it. I'll post the results next week.

 

One way or another it sounds like you might be running out of oil, whether its because you're pumping it all up top or because the pump is sucking air I don't know.

I'm not too sure about the whole HV pump thing though. The drain holes back to the pan are plenty big, the pump would have to be moving a lot of oil through some pretty small orifices for the drains to not be able to keep up.

 

I use a 7qt pan on my 388 but I had the builder cut the spring back on the HV pump. My psi about the same as you but, I don't lose pressure on load.
I had a bad filter once, syptom was constant pressure at 45psi.

 

i concur...

 

When you take your pan off, get rid off the high volume oil pump. You don't need any more volume or pressure than a standard pump, and engine only needs 10 psi of pressure for every 1000 rpms. A stock flow pump far exceeds that. A high volume pump takes more power to turn and it is more likely to break your pump shaft.

 

Call mythbusters

 

Right pal.

I've run a HV pump in every motor, from idle to 6500rpm and i've never seen or heard of any of this BS with the exception of folks on this site.

His tube fell off, or he has another problem.

-- Joe

 

You can probably remove the drain plug, drain the oil, and either shine a pen flashlight in there (not sure you will see anything), or stick in one of those small pen-size magnets on a stick and fish around to the rear of the pan. If it hooks something and clangs around when you move the stick, you have found the problem.

 

Thats a pretty good idea.

-- Joe

 

quote:
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Originally posted by pellmanm
When you take your pan off, get rid off the high volume oil pump. You don't need any more volume or pressure than a standard pump, and engine only needs 10 psi of pressure for every 1000 rpms. A stock flow pump far exceeds that. A high volume pump takes more power to turn and it is more likely to break your pump shaft.
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Right pal.

I've run a HV pump in every motor, from idle to 6500rpm and i've never seen or heard of any of this BS with the exception of folks on this site.

His tube fell off, or he has another problem.

-- Joe


And because YOU have run one in every motor,no way it could be anything but right,huh?

Yes,HV pumps CAN pump a pan dry faster than it can drain back.It's uncommon,but on occasion it does happen.
As far as it taking more power to run,I've never seen a head to head run on a dyno,but stop and think about it.The engine turns the pump.If the pump makes more pressure,it takes more turning power to make that pressure.It's a very small amount,I'm sure,but I'd bet good money that I'm correct on that point.
As far as stock vs. HV,I run my stock type pump to 8,000 or more every time I pull the Iroc out of the garage,and I've never had any problems with oiling.Not saying that's the thing to do,but it works for me.If you feel better with high oil pressure,run the HV pump,just make sure your running a large enough pan.

 

This issue sounds like either the pickup is too close to the pan, or there isn't enough windage control and the oil is being whipped into a froth.

To test if the pickup is too close to the pan run a thinner oil (lower weight) and see if the oil pressure issue subsides. If it does then there isn't enough clearance between the pickup and the pan for the oil to flow.

To test for windage issues run 1/2 to 1 quart less oil. If the issue subsides then better windage control is required.

Note: run each test separately.

I don't believe that the pickup fell off. The tell-tale sign of that problem is no oil pressure while braking and coming to a stop. This is caused by the oil going to the front of the pan as the pump inlet is at the rear of the pan.

RBob.

 

The theory of 10 psi for every 1000 rpm's has been quoted in various magazines such as Hot Rod, Car Craft and Popular Hot Rodding. They got their information from professional engine builders. Those same engine builders recommended a stock type oil pump for street applications that don't see more than 6000-6500 rpm's. Since they do this for a living, and I don't build and test motors even close to the volume that they do, I will accept their conclusions. H.V. oil pumps sucking the pan dry is also a problem that isn't quite as uncommon as most people think. There were some posts that gave the original poster ideas as to how to test for problems. Hats off to those guys. Not trying to dis anybody, but Rbob posted a really good thread that I think would be the best place to start for the original poster of this thread. That's just my

 

If you look on mellings web site they state a high volume pump will not suck the lower half of your engine dry. They claim it to be a myth actually. It would be a good episode of myth busters.

If you were to have a plug kit installed in the top of your engine it could be possible to run the pan dry at high RPM but I doubt this engine has an oil restriction kit in it. I'd be inclined to agree the pickup tube has fallen off or was installed wrong. Also possible the bolts have come loose on the pump its self but oil pressure would probably never see close to 40 if this were the case.


Edited BC my laptop keyboard is FUBAR.

 

I'll second that. I recently spent the better part of a Saturday afternoon removing my oil pan to reinstall and tack weld my pickup in place. Only symptom was lack of oil pressure on very hard stops.

 

^What he said.

 

Can youimagine the shop accidents they'd have on Myth Busters trying toprove or disprove that. Now thats what I call entertainment.

 

With my HV pump, if my oil level get below the middle of the dipstick "safe" zone, my oil pressure drops on load and if I close throttle it jumps back up. We very specifically setup my pickup to be on the bottom of the oil pan, so it would be safe to assume i'm moving so much oil, it's not getting back to the pan. I try and keep the oil level at the top of the dip stick (5.5qt) to help prevent that.

Now on the oil pickup, my last motor the pickup fell off, and at idle I had little or no pressure, but with some engine speed, it would pop up like nothing. SOMETIMES I would have pressure at idle, but not always, so I thought I had a bad sending unit or short. About 3 days later I spun a #4 rod bearing. My motor guy said that there was crap in the berings and the short block was not disassembled and cleaned or they didn't replace part (points to first senerio). He said I shouldn't have spun a ror bearing becasue of low pressure on idle, the crank should have been dipping into the oil, he thinks me lack of pressure was crap in the oil channels. Regardless, my pickup was welded on. The first time my guage twiches unexpectantly, i check the oil. I also spent a lot of money assembling a heavy duty bottom end. 2 spun rod bearings (one stacked) is enough for me. Thanks.

Edit: and as for the sucking the pan dry, i think it's more of a problem of my 1.6 roller rockers flinging oil all over the valve covers. I'd bet when it's running 3500-4000 there's atleast a quart of oil in either valve cover.

 

I had the exact same thing and it turned out to be the pickup was up too high and couldnt suck oil from the bottom of the pan, causing it to drop in pressure.

 

Tail, if your pickup is on the bottom of the pan, it's more likely that your pump can't pull enough oil in through it at speed, and the rotors start cavitating, causing loss of pressure. If anything, crap in your oil passages should have increased your oil pressure, not decreased it. There's no way your crank should have been hitting the oil either, unless you'd overfilled it.

I'm still not convinced on the plausibility of the pan being sucked dry. The only place that oil can go where it doesn't immediately run back to the pan is on top of the heads, and I don't see how the oil pump could move enough oil up there that it wouldn't be able to drain back through those huge holes in the heads and lifter valley fast enough to refil the pan. If the pickup comes uncovered at high RPM it seems more likely to me that either the pickup is high, the oil is too heavy, or the oil level is too low to begin with.

 

I still say that you can suck the pan dry with a high volume oil pump. Apeiron asked where the oil would be. I say check the crank, which is more than likely trying to fight its way through the thick mist of oil caused by windage. A high pressure oil pump on the other hand probably wouldn't drain the pan. That goes back to the Z28 pump spring kit that a lot of old school hot rodders used to use to increase the pressure. On top of that, a high volume oil pump will require more power to operate. Now the question becomes, is it the pump that steals that power or the windage it probably creates. This is a pretty cool benchracing topic by the way.

 

1st, I didn't say it was being caused by a pick-up tube that had fallen off. He asked what else it could be, that's one possibility.

I like the pick-up too high better, though.

As for high volume vs. high pressure, either one is dependant upon the clearances though which the oil eventually escapes from the pressurized system. If clearances are loose, a high volume pump will maintain the pressure. If clearances are tight, a high volume pump will by-pass and the excess flow is dumped back into the pan. If the clearances are tight, a high pressure pump will maintain pressure at lower RPMs, with the excess being dumped back into the pan via the by-pass. If the clearances are loose, a high pressure pump will require higher RPMs to maintain pressure.

Bearings are the main "dump" point from the pressurized system. The rest goes through the valve train.

High volume with loose clearances will put more oil in the path of rotating parts.

High pressure requires more power to operate than high volume.

 

This is the best description I've seen about the difference between high volume and high pressure oil pumps. This is from the Canton site and doesn't go into the possible problems, just the function of each different oil pump.

Pressure vs volume

Pressure is created by the resistance to flow. For example, the water flowing out of a garden hose has relative low pressure, but when you put your finger over the end of the hose, restricting that flow, the pressure within the hose increases and you see the result by increasing the distance the water travels as it leaves the hose. The resistance to oil flow Inside an engine is from the clearances of the bearing and lifter bore. Engines with increased clearances will require greater flow to maintain the same pressure. As the RPM of the engine increases more oil is required. The oil pump selected should be able to flow the volume of oil required to maintain the pressure desired. A relief spring within the pump relieves the pressure when it reaches the desired level. High pressure pumps have a higher pressure relief spring as also do most high volume pumps. The main disadvantage of using a pump with the ability to flow more than required by the engine resulting in this bypass opening is a very small loss of horsepower.

Now, back to the bench racing session!

 

Windage is still only going to account for a few ounces of oil which are suspended in the air before they eventually fall to the sump or hit the periphery of the crankcase and drain back to the pan. There are over 4 litres of oil that have to go somewhere before the sump is drained to uncover the pickup.

 

i agree with the pickup being off/too high. Another thing no one has even broached yet is the fact that he is running a solid roller with no restrictors in the galleys. Nearly any pump can suck a pan dry with no restrictors. I have the fried bearings to prove it. For those who dont know, hydraulic lifters restrict the flow of oil to the top end of the motor b/c of their design. A solid lifter on the other hand is a straight passage to the pushrod. The oil simply pushes straight thru to the rocker. The restrictors that the cam companies recommend do the job that a hydrualic lifter does automatically.....restrict the flow to the top end. The lack of restrictors plus a HV pump can very easily cause this problem.


edited for spelling

 

Restrictors redirect the flow to the bearings, where it's useful, instead of to the valvetrain, where it isn't. Even without restrictors, the oil going on top of the heads is going to drain right back into the pan.

 

Negative on that ghost rider...the restrictors are installed in the rear of the galleys between the feed from the main galley and the lifter galley's. They function by restricting the size of the feed hole, creating a ........wait for it.......restriction. They have no a magical abilites such as redirecting oil flow.

Food for knowledge, the actual galley is 3/8", the restictor, and there are various sizes, typically restrict to 5/16".

 

Take another look. They restrict the flow to the lifter galleys, redirecting flow to the main galley.

 

Actually, what you saying is exactly what im saying........the restrictor restricts the flow to the lifter galley.....therefore indirectly, b/c it is backing up the flow in the main galley, redirecting flow there. While technically to the letter of physics it is not redirecting flow, that is basically what it is doing. Too different ways of saying the same thing. Back to the original point tho, lack of restrictors in a solid equipped motor can cause this problem. INstall the restrictors and reassess.

 

What RPMs are we talking about? If engine speed isn't a factor then you need to look somewhere other than oil pump.

You stated the when you "stab it the pressure drops and when you lift it comes back". Sounds like something is moving out of place under heavy load. Cam could be walking and exposing some of the bearing, or I have seen it where with high volume/pressure pumps installed with the plastic retainer on the shaft, the shaft can flex at the retainer and cause the pump gears to run at an angle ( especially if there is any play in the distibutor shaft). Always use the metal retainer with these pumps.

As far as sucking the pan dry, your pressure would go to almost nothing.

 

not exactly...air is compressable..so it will build some pressure....the reason why the oil pressure doesn't go from 55 to 0 in the blink of a eye.

 

an oil pump is not going to compress air enough to move a pressure gauge. And I did say "almost nothing"

 

I'm still going with my theory about high volume oil pumps being unneeded. At a sustained RPM level, the stock oil pump has enough volume and pressure to have over half of the oil from the pan at the top of the engine. If the stock oil pump can do that, imagine what a high volume pump would do. 10 psi of pressure for every 1000 RPM's the engine turns is more than enough pressure too. Any more than that and you're wasting power. Let's not forget that these high volume/pressure oil pumps require more power to turn. Then there's the factor of roller cams made from steel or billet steel that require a bronze Distributor gear. The load these pumps place on the Distributor gear will cause wear a lot faster than the stock pump. Also let's look at the fact that one of the biggest problems with high volume oil pumps is a drop in pressure on well handling and fast accelerating vehicles. What do you think caused the drop in pressure. It's air being gulped by the pick-up when it should be oil. Now we have the situation I described earlier. The pan has been evacuated. You can use windage trays and trap door baffles in the oil pan all you want, but if there's no oil it's gonna be sucking air. Another known problem with high pressure oil pumps is that when the motor's cold you can actually split the oil filter in two if you rev it too high. I hope no one would do that, but it has happened to people. You know that little spring that allows oil to bypass the oil filter right. Well that's the spring that's overcome by the high pressure oil pump when the motor is cold. Even if you don't rev it, the high pressure pump overcomes this spring and sends unfiltered oil through your motor until the motor is sufficiently warmed up. Food for thought.

 

Yea I'm a couple weeks late getting back, ISP then whole computer problems.

Heres the link to Mellings site High Volume Pumps: Advantages, Myths & Fables

Good reading.

 

Thanks for all the posts guys, much valuable info was taken in. I decided to try a new oil pump and pan. Both are Moroso, an anti-cavitational blueprinted pump and a 7 qt. pan. Works flawlessly now! Pressure remains at least 60 PSI through-out. So either the better pump or the added oil capacity, or possibly both cured my problem. Now I just need to replace my tranny mount, as I broke it today shifting into 2nd. At least it's a cheap fix this time. Thanks again.

 

Glad to hear you got it fixed. Now after the trans mount is done, you can enjoy some of the last nice weather days.

 

hey, I was just scrolling through posts and found this, thought I'd share that I have the problem of loosing oil pressure if I run five quarts and punch it. If I only run 3.5 qts the problem disappears. I am running a stock replacement milodon pan and would like to know the best way to control this windage problem. Thanks for the help (45,000 miles and running fine, but will be pulling the motor to change cam again and add new heads, so now would be a good time to fix problem....I do have a stock gm pan for the car that is brand new.)

 

A windage tray and crankshaft scraper would probably bring your windage troubles to an end in short order. It probably wouldn't hurt to use an oil pan with baffles (trap doors) to keep the pump submerged either.

 

thanks, don't know much about this area (oil control), how difficult is fitting a crank scraper.

 

It isn't bad at all. Just remember that you'll need a stud kit for the windage tray. Milodon sells a complete kit for most vehicles, which I'd highly recommend if this is your first time doing this. The kit should come with everything you need, including studs.