SBC completely lost oil pressure-HV oil pump to blame?

I'm sure this issue has been covered before, but just a reminder to refresh anybody's mind thats interested. I've got a 56 Chevy with a '72 model year 350 shortblock. Just drove the car 300+ trouble free miles and two blocks from the house I stab the gas for a short blast up to 2nd gear and let off. Shortly thereafter I notice the oil idiot light is on and the pressure gauge read ZERO. Shut off engine and almost coasted right into the garage. Car would still start but no pressure.
Pulled distributor an hour later and used a drill & pump drive to spin the pump and instantly had pressure. Distributor gear looked perfect, as did the ARP pump drive rod. Ended up dropping the distributor back in again, engine started and had pressure immediately.
After a quick internet search and consultation with a couple sbc engine guru's, we've decided that my hi-volume oil pump may have just pumped enough oil at that time to suck the pan dry and gulp some air, starving the pump or something along those lines.
So next on the agenda was to drop the pan and oil pump and replace pump with something like a M55-A which is just a high pressure pump as opposed to a hi-volume pump.
Again, I'm sure this scenario has been played out thousands of times over the years, but just wanted to share it with all of you.

 

I've always run "high volume" pumps and never had a problem with that but I have to ask if the oil level was low when you checked it in the garage? The 350 in my 71 Daily driver truck doesn't like a low oil level.

The other thing is that is it possible that the oil pickup tube may have come loose? It could have become uncovered when you turned the corner and punched it at the same time if that was the case.

 

Just topped off the oil level the day before. Pickup tube was tack welded in place and still in place upon removal. Pump appeared to be secured tightly as well.
I'm just going to replace the pump with a different one and try it a few times to see how things go.
At first I suspected that the pump drive rod came up out of the pump and maybe fell back in but I don't think that is even possible.

 

I've always used a stock oil pump for all street driven engines with absolutely zero problems....save the non stock oil pumps for the racetrack engines !

 

X2 on a quality stock pressure pump. If you have room, a larger truck oil filter will give you a bit more oil.

 

More volume is more desirable than more pressure. Even so the stock oil pumps are well designed from the factory regardless of brand (Mopar, Ford, GM,Etc).Engine seals do not like too much pressure however the aim of the game is to keep bearings well lubricated

 

Fram filter ?

 

Ditto, no issues ever, using high volume oil pumps......


4TTRUK

 

I had a similar experience with a big block Chevy in my 65 El Camino: I rebuilt the engine...had a lot of expensive machine work done, and used good parts. I also installed a high volume oil pump, and I put a high pressure relief valve spring in it. It had killer oil pressure until I took it out to the drags and ran it. I noticed, on my last pass, that at the upper end of the strip, there was no oil pressure. I immediately shut it off and coasted to the return road where I checked the oil: clear full. After that, the engine still ran the same, but had oil pressure as low as 15 pounds at an idle, where before, it had been 55-60 pounds at an idle when hot. I couldn't remove the oil pan without pulling the engine, so I lived with the low oil pressure for a couple of years. When I finally did pull the engine to take a look, I found the rod and main bearings (the oil pump as well) badly scored. What had happened was that the high volume pump sucked the pan dry faster than the oil could drain back, so the engine had momentarily been oil starved.

Moral of the story: Don't run a high volume pump if you don't have a huge capacity oil pan. On a big or small block Chevy, the extra volume isn't needed, and it just costs horsepower to spin the pump. I had to learn the hard way...

 

More volume always goes with more pressure. The bearings would have to be worn out to increase volume without pressure. You can't have one without the other. Think of it this way, you have a straw that you are pouring water through. The straw is 1/4" diameter. You want more volume, you need to either increase the diameter of the straw or you increase pressure to get more fluid through the small 1/4" diameter. Now open up the 1/4" straw to 1/2" and if you don't increase the pressure, the volume will be the same and the pressure will decrease.

 

DO not use High Pressure pump.... I always use High volume. Melling or TRW... But it is personal preff.

The drive rod couldnt have become disconnected, unless its the wrong shaft, compare it with a stock one.

Look at the dist gear, and make sure the pin is secure and not stripped or faulty... If the pin holding the gear, and the pump drive peice is stripped or slipping, this would cause this... So will a stuck spring in the pump or the pin holding the spring in might have broke as well...

I am assuming you took the spring out before tacking the pick-up tube right? if not, then the spring is bad from the heat of tacking....If you did, the pin may not be installed right....

I hate when I cant find the culprit, then you never quite know when its fixed, and it will a;ways be on your mind when cruisin.... High voluum pumps are the way to go...

I n an extreme condition, your return oil passages could be blocked, causing all you oil to be pump to the top, and not flowing back down into the block... The return passages are at the rear or the heads, and along them as well.....Maybe some gasket material got hung in ther also....

WHen you hooked the drill to the pump did it cavitate, then load, or load from the get go..??

 

Some of us learn this over time. The larger truck filter adds more oil and a good stock pump is fine. Some headers don't allow the longer filter. In fact I had a set of long headers on the 55 wagon and had to use a short filter. Even less oil.

 

I'm not buying that the HV pump is the problem. The motor builders I know all quit using the High Pressure pump years ago and went to the High Volume Melling instead. I have been running the HV pumps for well over 30 years and never had a problem.

All this talk around the internet about HV pumps sucking an oil pan dry is nonsense. If you talk to the Melling engineers they will tell you that the amount of oil that gets to the top end of a small block Chevy (and many other engines) is regulated by the metering holes in the lifters. No increase in volume from the pump will make a big enough difference in the amount of oil going to the top end such as to cause the pan to suck dry. The increase in pressure of either HV/HP pump or the SV/HP pump is also not enough to suck a stock pan dry. If that is occurring it is due to blockages in the oil return paths from the heads to the block, which can be incorrect gaskets and or build up of sludge or corrosion in the passages, Or an low oil level in the pan. It can also be the wrong oil pump pickup.

 

I call BS. A high volume pump only pumps what the motor will accept at the pressure set. If the bearings are worn it takes more volume to maintain the pressure... and that extra oil is leaking past the bearing right back into the pan. And if the extra volume isnt needed the pressure builds to the relief setting and the oil just short circuits back to the inlet side.. never gets pumped into the engine. Heck back in the day we ran big block pumps on SBC's and never sucked the pans dry.
So is the theory that the heads are filling up to the tops of the valve covers? Extra available volume doesnt affect SBC upper end oiling since the lifters meter the oil flow up the push rods so I cant see where all the oil is being pumped to?

 

The Melling "M-55A" pump is fine, this is the same pump used by G.M. in all their performance units, Z-28, LT-1, etc.

The "M-55HV" is only necessary for loose bearing clearances AND does require at least an extra quart (or more) of oil!

Thanks, Gary in N.Y.

P.S. Also, get rid of the ARP pump drive, it isn't your problem but there was an issue with them! It may have been corrected by this time but I'm not sure! Use Melling's drive also, with the steel sleeve!

 

Interesting to read all the info/knowledge thats being shared here. I'm still fairly convinced it was the oil pump's fault, be that something stuck or malfunctioned inside of it. I took it apart and it looked fine as well.
I kind of wonder if the oil wasn't draining back into the pan fast enough as well. This engine has a pair of Patriot aluminum heads but they appear to have adequate drain-back capability.

 

Very little of the oil is pumped up into the heads. The vast majority is used lubricating crank, rods, cam and lifters. All below the heads, and not restricted in drain back. It's almost impossible to fill the valve covers and unload the pump. I'd look elsewhere for the problem.

 

Remember the series of tiny holes the oil has to go through to get pumped into the heads. I can't say nohow for sure, but I too am suspicious. More flow through bearings can't store oil out of reach, and I don't think it would be possible for oil to hide in the valley with all those drain holes.
I would be reeeaaal suspicious of regulator valve in pump hanging and bypassing most of the oil.

 

I have had regulaters hang on cheaper pumps, but my melling will suck a stock 4 qt pan dry under hard acceleration. I ran a 5 qt pan for a while and if it was a qt down my pressure would fuctuate wildly, now I run a 6 qt pan.

 

Agreed. Old wives tale.

 

I just talked to my machine shop buddy. He has been building engines for over 40 years. he agreed with what I said, that no way a high volume pump is "Sucking the Pan Dry"
He told me about a customer that he had years ago. Small block Chevy. 350, decent build up, 10.5:1 Compression, Duntov 30/30 cam, ported camel humps, good running motor in an 11 sec car. Stock oil pan, Melling HV pump set at 70 lbs. pressure. The guy hurt the motor and blamed Rick saying the pump Sucked all the oil out. They fixed the scored bearing and put it on the Dyno with the same pump and pan. Ran it up to 6500 and simulated a hand full of back to back 11 sec runs. Not once did the oil level cause any problems what so ever. They then talked to a guy at Milodon who said this one is real simple. The hard accelerations were pushing the oil away from the pickup and starving the motor, didn't have a dam thing to do with the pump. Solution? run it about 1/2 to 1 quart over OR better yet, get a baffled Drag Race pan. For street cars a bit higher oil level will normally cure the problem and still not cause excessive windage.

 

i had a melling m55hv on a 327. At high rpm the oil pressure would start to fluctuate. I talked to my engine builder, and he says its probably caused by cavitation in the oil pump from it trying to pump too much oil. I tried a stock bbc pump after doing some research and finding that its basically the same pump they used on the dz302 trans-am motors. Good oil pressure, and no more problems.

 

BINGO!!!!. been runnin high volume oil pupmps for 40 yrs.never once has one pumped the pan dry lol.and ive had a sbc hit 9,000 rpms a few times with a stock volume pan on it.never had any problems with the pump, thou i did spend alot of money on pushrods and bought a few extra roller rockers lol

 

For me, HV pumps are basically for customers that want to see 30+ lbs. of oil pressure at idle. That's about it. High pressure pumps are for engines that see lots of RPMs. Rule of thumb--10 lbs of pressure for every 1000 rpms.

Maybe your spiked the pressure, opened and stuck the bypass valve in the pump. It's happened before.

 

"Never assume anything" a law we had in the machine shop at work. For instance- how many of us has pulled a new pump out of the bag ,rinsed it off to get rid of the preservative oil, perhaps checked the cover screws , intalled the pickup ,primed it and bolted it on ?Assuming all is OK inside the pump? A fellow machinist did just that on a 351 C he was building for his Mach 1,when fired on the test stand ,the oil pressure climbed out of sight and the filter cannister ruptured. After trying a "racer" filter and splitting it wide open , he finally dropped the pan and pump , inside the relief bore was a teeny piece of debris that was hanging the piston and not letting any relief at all. Never assume anything---!

 

i had the same problem occur on a sbc i had. it was a way tired motor that i had with very low oil pressure. in an effort to bump the pressure up to keep the motor happy until i could rebuild it i dropped the pan and installed a high volume high pressure pump. the new pump did the trick (sorta) and the pressure was up but for extended periods of time on the freeway (not accelerating, just cruising) the oil pressure would start to drop and then go up and then drop... basically bouncing. adding in more oil made the problem go away. i chalked it up to the new pump sucking the pan dry (or nearly dry) to the point where it was picking up air. it would then instantly get more oil and the pressure would come back up but then it'd drop right back down. and like i said, adding in more oil fixed it.

once i finally did rebuild the motor (30 over bore, 10 under on the crank, new pistons, bearings, cam, etc, rebuilt heads) i put a standard pressure pump in and on the first fire up i had like 20 psi of pressure. i was soooooooooooooooo pissed! i yanked the pan off and shimmed the shit outta the bypass to get some pressure out of it. there apparently was something fundamentally wrong with the block because it was a completely fresh rebuild but it had low pressure to begin with so something wasn't right somewhere.

oh also, i used an 8qt pan once i rebuilt the motor. i keep lots of oil in 'er and never had a problem besides the annoyingly low oil pressure.

 

I like what you just said, that makes the most sense to me, something malfunctioned within the pump itself.

 

There is no reason to put anything but a stock Melling oil pump in that motor......period. Hot rodders think they need hi volume or hi pressure pumps but a stock pump with a hardened drive shaft will serve anything but a full on race car motor.

I agree that unless you ran it wide open for a long distance you didn't suck the pan dry. Either something in the pump malfunctioned, like a relief valve, or your oil filter caused some problem. Another possibility is that your gauge screwed up and was giving you a faulty reading.........I had to recently replace an electic sender as mine was dropping down into the low zone and a new sender brought it back to where it should be.

Don

 

I thought the same thing since he said he stepped on it up to second. Could the oil pressure problem/guage be from an air pocket from when the oil was briefly pushed away from the pickup??? In the other case the reason why it didn't do it on the dyno was no momentum to push the oil away from the pickup.

 

I had a roller timing chain break due to a Harmonic balancer grenade. I used a magnet to try and get all the grit out of the pan. It actually broke while turning over the car so I knoew there wasn't a bunch of crap throughout the engine. Anyway after thinking I got all the debris out, about 3 weeks later my oil pressure dropped to like 3 lbs. When it was cold it had about 15. When it got hot, 0. I poped the pan off and took the oil pump out. It had sucked up some small pieces of the timing chain rollers and then a piece got into the pressure relief ball and seat. I replaced the pump and I have 25 lbs at idle when hot. I agree, debris in the oil pump relief ball and seat. Even if new, take the pump apart and clean it. I know alot of people that have found crap in their Melling pumps.