Low oil pressure, intermittent low oil light

[Mogobs30th]

Im not sure whats up with the oil pressure in this car, but soon after I had rebuild the top end, and finally started the car, im having a problem with the oil pressure getting low.

When the car is cold and has sat overnight, the oil pressure is steady at 60-62 psi at idle. As the car warms up, id say about 15 minutes into driving it, the pressure starts going below 60, right around the 45-50 psi range. After about an a half hour, the pressure drops some more, down to the 30-40 psi range, and stays pretty steady in the 30-35 psi range for the rest of whatever trip I am on. It never drops below 30 psi, but at 1850 rpm, and the car fully warmed up, the pressure stays between the 30-45 psi range. Weird thing is that when the car cools back down overnight, and I start it in the morning, the pressure is right back up to the 60-62 psi range again. Im not real sure what could cause that, Ive had someone tell me rod bearings, which would make sense if the pressure constantly dropped and never came back up. But after it has sat for atleast 4 hours, the pressure is up again.

What could it be, oil pump, rod bearings, anything I may be missing? Im not sure what is causing this, any help is appreciated.

Thanks
Wes

P.S. The oil level is fine, EXACTLY on the hash marks on the dipstick at FULL. I also have a low oil light that comes when the car is cold, but goes away as the pressure drops and the car warms up. Any ideas?

[slow6]

Re: Low oil pressure, intermittent low oil light

60-62 is great
when the car warms up it is normal for it to drop a little but not all the way to 30! As oil gets heated it gets thinner (normal) so your pressure goes down a little.
I had someone tell me my low oil psi is worn main bearings or the wrong size main bearings. I believe this guy
Sorry, I cant help you without looking inside it

[slow6]

Re: Low oil pressure, intermittent low oil light

he went to ranken tech
here is what he said about main bearings:

"they have to be within .005-.010" clearence between the bearings. any less and oil wont lubricate well, any more and the oil doesnt have enough restriction."

I had my crank polished then got stock size main bearings

[Mogobs30th]

Re: Low oil pressure, intermittent low oil light

Im going to try checking, and possibly changing the oil pump gerator. It seems to be an easy change, and I believe that it is a possibility.

[slow6]

Re: Low oil pressure, intermittent low oil light

I guess it might be a possibility?
I dont see how one can get worn out!

God help you, you're only getting responses from me (I'm not an expert at all!)! LoL

[slow6]

Re: Low oil pressure, intermittent low oil light

this is what that dude said to me:

"""the 2 main causes for low oil pressure are bad main bearings and a clogged oil pick up""""

and I know my oil pickup isnt clogged, I cleaned it myself (its inside the oil pan)

[Mogobs30th]

Re: Low oil pressure, intermittent low oil light

I may also try cleaning the oil pickup tube, that is a little harder to get to, but I figure the gerator could be worn, by means of clearance issues. Could be that the clearances around it are not quite to specs anymore. But the pickup tube is definitely worth a try as well.

[slow6]

Re: Low oil pressure, intermittent low oil light

you could just pull a timing chain cover off a junkyard motor
If the engine is in the car, you have to get a lift and pull the motor a little upward so you can get the oil pan off (which is hard to do since our motors are soooo far back in there)
I really feel sorry for you and I feel sorry for myself! lol
GL!

[CDNFB]

Re: Low oil pressure, intermittent low oil light

I had my crank polished then got stock size main bearings

When you dropped the crank I thought you plasi-gauged it to check for the proper clearances. Were they not within limits? Cause if the mains were within the published limits then that shouldn't be the source of your low oil pressure.

[CDNFB]

Re: Low oil pressure, intermittent low oil light

Mogobs30th: I agree with the idea of the clogged or restricted oil pickup, but also make sure the pick up isn't loose as well. If the pickup tube is loose it could be drawing in air and cavitating the pump which would also affect oil pressure.

Also, if your going to pull the oil pan to check the oil pick up, it might be a good idea to pop a main bearing cap off (or 2, or 3, or whatever is accessable) and then do a plasi-gauge check on it(them) to see what kind of looseness you have. Your going to be in there anyway.

[slow6]

Re: Low oil pressure, intermittent low oil light

do you think getting the crank polished would grind it down that much to need a different size bearing? crank had 32k miles

[Mogobs30th]

Re: Low oil pressure, intermittent low oil light

Ok....IF it is the rod bearings, which I still have done nothing to support nor deny that, would the WHOLE engine have to be ripped down to replace, or could I do it without tearing down the top end?

[slow6]

Re: Low oil pressure, intermittent low oil light

you would definately have to lift the engine, drop the oil pan, change the rod bearings (if thats all your gonna do???) you have to do it without disturbing the rings (if you take the piston out you should put in new rings, which might be impossible to do without taking off the heads).
I dont know how hard it would be to do, but I would like to try it sometime.
I know how bad it sux to be under a car on jacks, I do it all the time.

People just like to have a nice clean area and putting it on the engine stand for it to be kinda easier to do.
Feel free to ask more questions
GL!

[Mogobs30th]

Re: Low oil pressure, intermittent low oil light

I would pull the engine, I just don't wanna tear down the top end again.

But, if the pistons are taken out, they HAVE to be done from the top, thats a given. I think it would just be easier to pull the engine, tear down the bottom end, replace the rod and main bearings, then rebuild, without touching the top end. All on an engine stand of course.

[CDNFB]

Re: Low oil pressure, intermittent low oil light

do you think getting the crank polished would grind it down that much to need a different size bearing? crank had 32k miles

Usually polishing only removes a very small amount of material. If more material was needed to be removed to ensure a proper surface, the machinist would have ground the crank journal then polish it.

Either way, you should have plasti-gauged it on assembly to confirm the clearences were right.

But, if the pistons are taken out, they HAVE to be done from the top, thats a given. I think it would just be easier to pull the engine, tear down the bottom end, replace the rod and main bearings, then rebuild, without touching the top end. All on an engine stand of course

Yes you could do it this way, but it's not the best way.

Are you running a completely stock engine, or has the internals been modified?
I ask this because (and I just stated this in a previous post) if your engine is completely stock and your only going to rebuild to stock, you probably better off getting and installing a low milage used engine from the wreckers.

Evaluate what you want from this engine (in terms of reliability and longevity) with your options of used engine replacement, proper rebuild at machine shop, or just slapping in a set of bearings. Don't expect the engine to last very long, or handle high HP or extended heavy duty use if you just slap in a new set bearings.