[monkeyboy]

Engine is a 396 - low miles. It was rebuilt by a friend.

The problem is the oil pressure drops about 10 lbs when motor revs from 2000 to 4000 rpms.(40 lbs down to 30 lbs). I got 5 opinions from non experts.


1 The oil pump pickup fell off

2 The high volume oil pump is sucking the pan dry

3 The oil pump is on it's way out

4 The bearings are shot

5 The pickup screen is dirty


Who's right? Im going to pull the motor in a few weeks and change the oil pump. Is there something else i should look for or check. I don't want to re install the motor and have the same problem. Is my oil pan too small? I'm driving around looking at the guage instead of looking at the road. No fun.

I did change the guage already. Both were mechanical and both read the same. thanks guys.

 

[chev64]

while you are in there, take a look at the bearings to check wear.

------------------
Leo Paugh
Maryland Chevelle Club #017
A.C.E.S.#3731
there is only one way to fail, and thats to quit.
Maryland Chevelle Club

 

[chev-hell]

is this when your moving?? if so are you romping on it?? if it is my guess is your pump is pumping a LOT of the oil in the pan to the top end and it's taking longer to trickel down, thus making less in the pan at most times, and when you "punch" it, the oil "snaps back" into the back of the pan (much like your neck

) and the pick up is sucking a bit of air...
mine does exactly this when it's a quart low. but i run 70+lbs of pressure most all the time...

------------------
1970 SS396 AKA 454/4spd
My Chev-Hell Page
GOLD Member #783
Ft.Worth, Tx
(OO=ss=OO)

 

[DaleM]

Kinda same boat but my engine has about 70K on it now. After sustained highway speeds of 70/75, oil pressure fluctuates between 40 and 20...slowly drops then slowly rises again. Drop to 60 mph or so and it's fine. I tend to think it's the oil pickup being too high and starving for oil at higher speeds (about 3000 rpm in this case). In my mind, the fact that you've still got 30 lbs would lead me to believe #5 of these choices.

The pickup should be about 1/4" above the floor of the pan if memory serves and should be tack welded or staked to the pump. So, here's opinion #6 I suppose, pickup could be loose or not adjusted properly. Nothing against your friend, but this might not have been checked.

I'm tearing mine down in a couple of weeks for a rebuild and that's one of the first things getting checked and replaced.



------------------
Dale McIntosh
TC Gold #92/ACES #1709
67SS & 67 Elky
http://www.dalesplace.com

 

[Al]

6. Throw the oil filter away and try a new quality brand filter.

(cheaper than fixing all the other solutions and you never know...

 

[charbilly2001]

Ok guys first off there are exceedingly few engines in this world that oil better than a chevrolet V-8 bb or sb. if your oil pump is working properly and you accelerate there is absolutely no way that the oil in your sump will go any where but directly to the pickup. Additionally there is no "high volume" oil pump made that will pump more hot oil up into your engine that can drain back into the sump per unit time. There are more than enough drain holes in your engine to get all of the oil back into the sump for virtually any street/strip application. The first thing that comes to mind for your problem is that the oil pump pickup has either fallen off (this happens more often than you think after a rebuild) or has been installed improperly. I don't recall the spec but I think the pickup should be about 1/16th to 1/8th off of the sump floor. Visually it should look parallel to the sump floor. if it is tipped up very much at all it will potentially suck air under acceleration. That would give you some unusually low readings as you say. Any worn bearings that would give you the kind of pressure drop would also rumble when you start the engine and before the oil pressure comes up. In other words there should be other signs beyond pressure fluctuations from bearing wear. If your friend didn't "tack" the pickup to the pump body you should have it done the next time you are in the crankcase. Good Luck

 

[monkeyboy]

Thanks, I'll tell you what i find next week.

 

[SS_Dave]

I agree with chairbilly??

Although 1/16 to 1/8 is too close to the pan. I would put it no closer than 1/4 and preferrably 3/8 to 1/2 inch away. I think you r pickup is the problem either way.

 

[EdCarpenter]

I had a similar experience with a 400 small block. All new internal parts and HV/HP oil pump. I would be just going down the road and the oil pressure would go from 65lbs to 10lbs. I would stop and leave it idle and after a couple of minutes the pressure would recover. Oil level was good. I experimented with several small fixes. I even changed the pump to std. pressure, new pick-up and pan. Same problem. I remembered, during the rebuild, I installed screening in the intake valley to keep any trash out of the pan, if the engine would break on the top end and plugged the holes above the cam to reduce hot oil from dripping on the cam and splashing on the intake. I removed the intake and likewize removed the plugs and screens. The problem was gone. Just in case you did the same thing, this was a learning experience for me.

Ed C.
70SS 396/350 4 speed red/white
70SS LS6 project
65 corvette coupe red/red

 

[Randy Mosier]

The only thing that comes to mind is air is getting sucked into the pump. I don't think it would be a relief valve spring because it wouldn't hold 40 PSI and then drop off to 30. Check the pickup tube very carefully for cracks when you remove the pump. Look at the screen also to see if it's partially blocked, then I'd replace the tube anyway.
Just for peace of mind, pull a couple of rod and main caps and and look at the bearings.

 

[charbilly2001]

SS_DAVE I like your numbers better than mine. A 1/4" sounds more like it. Thanks for the correction. Ed Carpenter you are one lucky dude! I hope that screening didn't do your engine any harm.

 

['70chevy]

Just a tip that someone gave me. I have a BB and use an AC 932 truck filter, that holds about 1 & 1/2 qt. of oil. Kind of like an extra insurance against oil starvation for whatever reason. (unless the pickup is the problem of course). Some headers will prevent this filter from being used, but my 454 and Hedman headers present no problem. I like the extra capacity and the extra filtering! Just my .02