has anyone ever heard of a faulty oil pump?

['70_402]

we started my motor up and broke it in yesterday but i don't have very much oil pressure at idle... i have plenty when motor is reved but only about 10 at idle... the guage responds well and goes right up when reved... we thought it was a clogged filter so we took it off and there was some metal shavings in it.... yea, uh oh. but we think it might have been straight from the pump... cause there is none at all in the pan...

any thoughts?

[special-K]

It wonder if there`s too much bearing tolerance.Maybe a wiped bearing(s).I hope not,but it sounds like the pump is working.

[geoman]

If I were you I would tear it down to be on the safe side. Sounds like a bearing to me too.

I did hear of the melling M55 pumps being junk. Is this what you have?

A regular pump should be around 20lbs idle and go to about 40-45 at cruising speed. If its a high volume then more.

[haysonj]

I had one of mine that i didn't replace when I rebuilt the motor that had gunk in the relief valve and it was stuck open and would show no pressure at idle. Now I always replace with new as they don't cost that much compared to losing your bearings

[Billla]

You can easily tell by taking the base plate off the pump.

I don't buy parts store pumps any more after 3 pumps in a row from NAPA were junk with too-tight clearances. The pump should operate easily by hand...if it doesn't, it's junk.

Stick with the Melling performance pumps, even for street use.

A bit of gunk in the filter after break-in isn't ALL that unusual depending on the ring material.

[umwtnt]

There is a plug on the small block that if left out it will show the same problem. Also if the cam bearings have not been replaced or installed correctly there is the same results. The block is in the back of the block But, I do not remember excatly where as it has been a while since I've built one. A teardown is definitely the safest way to go. My fault I see your a big block man, Way to go. But a tear down is still the only way to go. But check to make sure the oil relief valve in the filter block is not stuck open.

[truckdude239]

the plug is under the rear main cap

[70GMCer]

Engine at operating temp, 10 psi for every 1000 rpm is the norm for a sbc.......I'm not saying there's nothing wrong with your engine, just that most normal oil pumps will be around 10 psi at idle & go higher as the engine revs.

[Billla]

Originally Posted by umwtnt

There is a plug on the small block that if left out it will show the same problem. Also if the cam bearings have not been replaced or installed correctly there is the same results.

If the plug under the rear main cap is left out there will typically be ZERO oil pressure.

Typically if the cam bearings are installed incorrectly so as to block the oil hole there will be very HIGH pressure.

The machine shop should have installed the plug under the rear cap, and as a home rebuilder this is something you should a) always ask about and b) always check

['70_402]

we put the motor bearings and all together ourselves... done it alot... bearing clearances were fine, but i agree with you guys that a tear down is in order... sucks man... but better now then when i have to beacuse the motor is junk. man this sucks, the motor starts and run GREAT.... sounds freaking amazing... but oil pressure is the life blood. so it has to be done.

[67ChevyRedneck]

Buy a new oil pressure gauge before you do anything.....

[Andy4639]

I think it's a hit and miss. The pressure sounds about right for the info given. The metal shavings well did they come from the new pump itself being made. I mean it sounds as though it's fine.
It's your motor though and you have to be satisfied.

['70_402]

yea we hooked up a mac tools test guage up to it and it read the same... i think the pump is bad... but who knows... it was a brand new (i know that's not saying anything) melling high volume unit...

here's my next question... what causes it to have more oil pressure at startup and then drop off... just the temp of the oil itself?

[Blue_71]

oil temp plays a big factor in the drop off. did you put new cam bearings in this engine?

a high volume pump is generally not needed honestly.. they have the ability to drain the oil pan and have it all in the top end, with none in the pan. im running a stock replacement pump in my K20, and hold 45 psi at idle, at 195 degrees, and 70 psi at 2200 rpm at 195 degrees

[stope4]

Oil pumps do go bad. I know hindsight is 20/20, but why would you rebuild the engine and not replace the oil pump? There too cheap not to replace. Second, my oil pump did the same thing you are saying, except I started noticing almost zero pressure at idle after highway driving. I removed the oil pan, replaced the oil pump and rear seal, checked my rear bearing (did notice some scarring but decided not to replace). Because of the scarring, I went with a high volume pump. Now my oil pressure at start up is almost pegged but after the engine warms up it's sits about halfway up the guage at idle. When running it sits halfway between pegged and half. I realize the bearings are an issue but I don't feel like rebuilding the engine at this time.

Blue 71, I've heard the oil pan could drain story before, but I just can't seem to figure out how this could happen using the engine in a normal situation. Five quarts of oil in a regular oil pan is a lot of oil. If you have an aftermarket oil pan the sump could even hold more oil. Surely, if this was a huge problem on streetable vehicles, there would be warnings about draining the oil sump and ruining your engine. Or, they would not sell them, especially if it could ruin your engine. Has anyone on the board physically experience a high volume oil pump draining the oil pan in a streetable situation? How about racing? details please. Let's hope this doesn't go down the "friend of friend said" or "I heard" path.

[crazy longhorn]

Originally Posted by stope4

Oil pumps do go bad. I know hindsight is 20/20, but why would you rebuild the engine and not replace the oil pump? There too cheap not to replace. Second, my oil pump did the same thing you are saying, except I started noticing almost zero pressure at idle after highway driving. I removed the oil pan, replaced the oil pump and rear seal, checked my rear bearing (did notice some scarring but decided not to replace). Because of the scarring, I went with a high volume pump. Now my oil pressure at start up is almost pegged but after the engine warms up it's sits about halfway up the guage at idle. When running it sits halfway between pegged and half. I realize the bearings are an issue but I don't feel like rebuilding the engine at this time.

Blue 71, I've heard the oil pan could drain story before, but I just can't seem to figure out how this could happen using the engine in a normal situation. Five quarts of oil in a regular oil pan is a lot of oil. If you have an aftermarket oil pan the sump could even hold more oil. Surely, if this was a huge problem on streetable vehicles, there would be warnings about draining the oil sump and ruining your engine. Or, they would not sell them, especially if it could ruin your engine. Has anyone on the board physically experience a high volume oil pump draining the oil pan in a streetable situation? How about racing? details please. Let's hope this doesn't go down the "friend of friend said" or "I heard" path.

I have run a hy vol pump with several stock pans without any problems.....but have been told by a local speed shop "this is fine, but dont buzz the motor when the oil is cold" This can pump the pan dry, or if you wind er out on a long stretch of hyway, you could have problems. I run a melling 10555 (hy vol/hy press ) pump on my 383, with an old 6 Q 1 ton truck pan. this works fine(45psi hot @ 850 rpms, & 72 psi hot @ 3000). I do prefer a bigger than stock pan with a big pump. crazyL

[LONGHAIR]

Has anyone on the board physically experience a high volume oil pump draining the oil pan in a streetable situation? How about racing?

No....but I have always "heard" the storys too.
I think it is based on flow-back....the pump could pump the oil to the top end faster than it could get back to the pan. I'm thinking you would have to have a pretty gunked-up mess for that to happen....I think it would be pretty smokey if that happened


That said, you really don't need a high-volume pump. They are physically different from high-pressure. The rotors are longer and the cavity where they sit is deeper to hold them. These longer rotors physically move more oil at the same RPM as the "regular" version. This "more" comes at a price....greater load on the input shaft that drives it, which also translates to greater load on the distributor gear and camshaft. None of which is worth gaining oil volume that you simply don't need.
High-pressure pumps use a stiffer spring in the releif valve that regulates the maximum output pressure.

[stope4]

I agree that high volume is not necessary, but I do believe they serve a purpose, especially when you have loose or slightly worn bearings that can give you 20 or 30 thousand or more miles. And, since I'll probably will never put 20K miles on the truck, I went the HV melling route.

[Blue_71]

i had always "heard" the stories and never believed them untill seeing a friend of mines engine. this was however a high volume AND high pressure pump.. the engine was completly rebuilt. once it ran for about 10 minutes, it would drop off oil pressure. of course first thought was bad pump. replaced the pump, same thing.. replaced the pump one more time for good measure, same thing. put in a stock replacement napa pump, and it held good oil pressure from then on

[Yukon Jack]

In relation to the high volume pumps, I've read the argument that they take a bit more power to run and don't really offer any benefit for a street type motor.

[crazy longhorn]

On a street eng ,that you dont run past 5000-5500.....no a hyvol pump is not needed A lot depends on who you talk with (what builder), but an old rule of thumb was 10 psi per 1000 rpms that you plan to run the eng. some builders will say that a stock pressure (hy vol pump) is the way to go on a street/strip app. I have also seen a hy pressure pump (Z-28) used in the street strip app. It is also true (as mentioned) that these big pumps do cost some power to run some of use do go a bit overboard(guilty myself) on the oiling system, but feel better safe than sorry. A little extra in the oiling dept doesnt hurt, if you really plan to "zing" that bad boy up.....crazyL

[jgrh64]

always fill the pump with Vaseline or white grease prior to installing unless you remove distributer and manually prime the pump prior to starting.On a street rebuild a regular pump is fine on a high mileage engine use a high volume pump and a race engine (loose bearing tolerances) a high pressure pump