oil pressure drop when warm

[Aggravated_78]

I recently bought a 1978 monte carlo with a fresh rebuild 350 motor ( as i was told from the previous owner). when i start the car the oil pressure on the dash acts up so instead of having it electic i go direct with an after market gauge. When i first start it up it reads 40 psi. As it warms it drops as low as 5psi, ok. when i drive it at cruise speed it averages around 20 psi when i lift my foot off the gas to make a turn and start breaking it goes down below 5 psi . i have no idea what type of oil the previous owner has in it. . just to add if im looking at the motor from the front, inside the left valve cover makes a small ticking noise. Any helping hand would be greatly appreciated

 

[RITTER]

5psi is pretty low ... any receipts proving the rebuild :?: 15-30psi is pretty normal for a completely warmed up engine. I would also possibly check your oil pump pick-up. There is a chance that it has come loose or fallen into the oil pan. The pump can still get some oil (as long as the level is up) without the pick-up tube in place. This happened to a buddies engine in the past.

 

[Peter]

under 5 psi is certainly low. I believe the lowest spec for most engines is inn the 10-15 range. I would check the accuracy of the gauges to begin with but after that you could be looking at something like a partially blocked oil pump, over worn bearings, blocked passageways. There are a lot of possibilities to look at for low oil pressure and none of them are any fun

 

[81Regal]

5 psi is a little low, 10 psi for 1000 rpm is a good rule to go by.
Change the oil and filter, use quality replacement filter with 10/30 oil to see if that brings the pressure back up.

 

[91hrdbdy]

I'd be willing to bet that the oil pump was never replaced when the rebuild was done it often times over looked. The good news is you can change the pump with out pulling the motor. It's a little bit of a pain in the *ss but I've done it twice on the gbodys.
First pull the motor mount bolts and use a jack to lift the front of the motor from the crank pulley as high as u can remove the pan an u can slide the pan out the back of the car and swap ur pump and replace the pump shaft while your at it buy a new pan gasket and reinstall the pan. Takes about 3 hrs

 

[monte olrac]

That pressure is ridiculously low, I would do what every one else is saying first

1. Oil / Filter change (make sure you check for metal in the oil)

2. Gauge accuracy

3. pump pick up check or pump change

Any of those will be you best case scenario, Now for the most probable...crankshaft ground down and standard bearings were used, by fresh rebuild he meant some gaskets and maybe paint or just paint , or the crankshaft needed to be ground down and they slap in some new bearings and called it a day.

that ticking you are hearing is probably a collapsed lifer from a lack off oil,

I have made my share of mistakes on engine building especially when I was on a time and money budget, when i put in my crank and new bearings i didn't get the crank check and i could see it had groves and all kinds of crap wrong i just slap in some new bearings and kept it moving, my oil pressure was around 6psi hot at idle and wouldn't go above 40 - 45psi at speed when hot, but at start up i would still read 65psi. If those first three options doesn't fix the problem you'll need to pull that engine and do a real rebuild.

 

[Aggravated_78]

thanks for all of your inputs. i just came back from the auto parts store and i grabed some oil, oil filter, and a oil pump just in case the oil change diddnt work. ill get a jump on it as soon as this weather gets better. i will keep ya'll updated as i progress. Like i said thanks in advance.

 

[Highwood Malibu]

x2 on all of the above suggestions also you may have a bad sender unit on the back of your intake manifold. I know on my old engine my oil pressure was always wrong because the sender was incorrectly installed and it shorted on the bottom of the distributor, do the gauges jump frantically when you rev it?

 

[magik420]

This forum and you guys are absolutely awesome. As a NOOB to this place i was looking through topics and came across this one. About a month ago i swapped my 5.7sbc from my caballero to my 84 Monte, in the process i replaced the oil pump timing chain and all gaskets just to keep it fresh. for the first couple weeks my oil pressure was a normal 25 at idle and 50 when driving. then last week my oil pressure would drop to 10psi after about five minutes of running, but went to 50 when i drove. so after reading this post i jacked up my car and started to look in to it. When i hit my fist on the bottom of oil pan i could hear what sounded like a bolt laying in the bottom. Awww FML that's not good, so yesterday i pulled the pan and sure as sh^t there was 2 bolts from the oil pump in the bottom and the other 2 were almost loose. so i cleaned it up and used red loctite and lock washers, put it back together and now it is 25 again. Thank you guys for this topic and knowledgeable information that saved my motor from a catastrophe.