low low oil pressure after warm HELP

[Custom 68]

I followed the previous oil pressure debate and problems but wanted new opions. We just recently rebuilt my 327 I have put 10w30 oil in it for start up after running it the breakin period I changed it. Now at startup when cold the pressure at idle is fine at 50 or so psi. After the engine reaches temp at 180 or 190 the pressure drops to a wapping 5 psi at idle and up around 15 (maybe a bit less) at 1000 rpm and 20 or so running down the road at 2000 rpm. I have changed the filter to a ACDelco but didnt help.
everything is new (except the pistons and crank) what could cause this? I am thinking about changing the pump (it is new)? I really dont wnat to pull this motor I just painted the truck and didnt want the extra trouble. I am running tpi so the wiring just adds to the pulling problems.
any thoughts it is very disconcerning to look down and have almost zero oil pressure at idle...
thanks
Dave

[chevyfarmer]

That is a bummer, especially when you just get it back together....

You said everything is new except crank and pistons. Did you have the crank turned (machined down) and put in new bearings? How about the cam? Did you have new cam bearings installed? These are two areas where you could be losing some pressure

What was the motor like before the rebuild, did you drive it?

[Bamm]

Smokey Yunich (one of the greatest small block builders of all time) guidelines say 10lbs of oil pressure every 1000 rpm's. While not what I would expect out of a rebuilt engine, you are within guidlines if as long as your oil pressure continues to climb through the rpm range. I wouldn't be to happy about 5lbs at idle though, that just seems low. ... my .02 .....Jerry

[Custom 68]

Yes I drove it alot before the rebuild everything was good I rebuilt it about 15 years ago and put 80000 or so miles on it. The cam is new and has new cam bearings. This has been along process but I think the rods were resized but the crank was not turned (It may have been) I need to find my recipt.
I was just unsure why it dropped that much after it was warmed up. I know the oil will thin but that seems like alot.
If I have to pull it I guess I will replace the main bearings again?
Thanks
Dave

[ksamps01]

I would think that if you didn't get the crank turned and new bearings to match it, that is probably where your oil pressure is going. Even if you replaced the bearings if there is too much clearance with the crank journals you won't have good pressure.

On the other hand, mine runs about 7psi at idle and 35-40psi going down the highway. I haven't heard anything clattering yet so I am not too worried. The old girl hasn't left me stranded yet.

Just my .02.

[junkyardjohn]

I AGREE WITH KSAMPS01 & CHEVYFARMER . SOUNDS TO ME LIKE THE CRANK WAS NOT TURNED, OR YOU HAVE TOO MUCH CLEARANCE BETWEEN THE CRANK & THE CRANK BEARINGS. I LIKE TO RUN A LITTLE THICKER OIL, LIKE 10W40 IN THE WINTER & 20W50 IN THE SUMMER, BUT I LIVE IN THE HIGH DESSERT WHERE IT GETS DOWN TO 10 IN THE WINTER & UP TO 100 DEG.S IN THE SUMMER. JOHN

[Custom 68]

Thanks ksamps. I honestly dont remember if the crank was turned. I would have thought it was but now I dont know or remember. I will be heading out again in a few minutes and will listen close...
I really hate to pull this think out...again.
Dave

[shortbed70]

My 65 chevy ha a jasper rebuild 355 with a comp cam and when I first start it oil pressure is at about 60 or so but when it warms up 185 it drops to around 10 in nuetral and about 6 in gear. I've run it this way for a year now with no problems and this is a crate motor so I don't see a problem with it as long as the pressure climbs with rpms. Did you soak the lifters in oil before you put them in? I've seen where this can cause this problem on new engines. Just a thought.

[cableguy0]

i have seen more good running small block chevies than i could count that had that exact same condition and everyone of em lived a long and happy life. i run a 20w50 synthetic basically because i run the dog sh!t outta my motor and it will get down to about 10 coming to a stop after a nice long highway run

[Robert1970C20rstbukt]

I use 20W50, and the needle on the stock oil pressure gauge always stays at the middle mark when idling and when you drive down the road it's almost bottoming out on the H side. 'Course I have a high pressure pump too so that might have something to do with it.

[oldsub86]

I rebuilt a 302 F**D about 2 years ago. Pretty well everything was done on the motor. It had a bad bearing on the crank prior to the rebuild so we put a crank kit in with matched bearings. I had the big end of the rods resized and new pistons installed as we bored it 40 thou over. It has a new cam and new cam bearings and lifters. I put in a high volume oil pump. If my aftermarket guage is accurate, I am getting about 80# cold and about 50 to 60# when hot at idle. I have heard that too much oil pressure can cause problems but this does not seem to be causing any problems.

Are you sure your guage is accurate? I have an oil pressure test rig that I made up. It is a small diameter hydraulic hose with adapter fittings and a guage on one end. I put the other end onto the motor to test to see what the oil pressure is.

[CHEVIBUBBA]

gm recommends a minimum of 5 psi at idle when at normal operating temp.
notice i said "recommends"?
due to your lack of info on this engine rebuild, i hesitate to comment.
you mentioned you were using 10-30 for break in.what viscosity are you using now?
did you see the same thing during break in?
this is a good example of why you should always check & recheck dimensions during a rebuild.
sounds kinda loose to me if the oil is thicker than 10-30.
i don't trust anyone with my blueprinting.i do it myself.

you can pull the pan, pull3 of the mains.instal some plastigage & follow instructions.
this will give you an idea of what the mains are at.
you can do the same with the rods.
if the plastigage checks outside of the specs for your engine, pull it & do it right this time.
you may even have the wrong bearings for the crank grind in it.
if the crank was turned .010" under & you have standard bearings in it the results could be similar.

[VetteVet]

5 psi is low for a rebuilt especially when you get 80 cold. I would try running a 20/50 or straight 30 weight. Did you clearance the bearings when you rebuilt to see what you had? I think you will see a difference with the heavier oil, but as long as you get 5 psi at idle and it climbs with rpms you should be fine.
VetteVet

[dion]

15psi at 1000 rpm's? that doesn't seem too bad, could be better though. 5psi at 1000 then I would worry. right now I'm at around 18 psi at 800-900 rpm at idle after geting off the freeway using 10-40, try 20-50 and see if that helps.

[Custom 68]

Thanks guys I think I may just pull it out to disect it... Yes I thought I checked everything but may have missed something. at initial startup and cam break in it wasnt like this it has gotten worse. I will see how my time goes but will update when I pull it and tear it apart. I will slow down and check and recheck everything.

[CPNE]

Ok, here's to obvious that has not been asked. Do you know if your oil pressure gauge is accurate?

[67ChevyRedneck]

5 psi at idle and 15 psi at 1000? What is your idle...do you mean in gear? My truck runs about 700 idle and about 500 at idle in gear. I'd try some different fileter/oil combos before I pull the motor, and I 100% agree with CPNE, I'd spend another 30 bucks on a new gage and check the connections to it before I would pull the motor. As a side story, I bought a sunpro temp gage and it kept reading that my motor was running at 230 degrees. I changed the thermostat several times, I had already put a brand new 3 core radiator in it, changed water pumps, added a brand new flex blade fan....turned out to be the damned gage. Best of luck to ya.

[Bowtiefreak]

Originally Posted by CPNE

Ok, here's to obvious that has not been asked. Do you know if your oil pressure gauge is accurate?

Exactly what I was going to ask.

[tab a]

FWIW--my pressure was reading somewhere near 0 (!) at idle, on two different guages. Changed to 20W-50 and it now stays close to 10.

[Custom 68]

Boy jeff your should be mister obvious (you know from Bob and Tom)...Of course I am joking you are a wealth of info. I will get a new gage to check but it was working before the rebuild. At initial startup it will read 50 but shortly after startup it will drop to almost zero. it is a mechanical gage I didnt see any kinks in the line and no leaks from it but yes it is a good avenue to check.
I have tried 3 different filters on it. The lifters are making a bit of noise at different speeds on the short trip I have made.
The engine is fresh enough that if I take it apart now mabye nothing has self destructed yet...
again thanks guys
Dave

[SWINGSAX68]

Hmmm.....I have just had to deal with a very very similar problem.....
I had about 5psi at idle when warmed up....a low deep knock only at idle in gear, and only about 15 psi street cruising. I have had it for months.....I have been like letting it sit waiting to get some cash for a new motor. I got some cash, just recently I decided to take a chance on changing the oil pump because i did have oil pressure at higher rpms.....well....2 hours later it did the same thing...low pressure, low deep knock, decent pressure at higher rpms..the oil pressure did improve, and I am running 2 quarts of LUCAS oil stabailizer....helps the knock considerably....it takes me every where I go in and out of san marcos and san antonio....its a bearing in my case....so I'm hopeing it lasts till the end of may so I can pull it and drop a 350 in it. Now I only get very low oil pressure at idle only when driving on the freeway more than an hour or so. but its a dying 305 for me.

[CHEVIBUBBA]

sounds like you may have wiped out a bearing.
if it was doing good but then went to what you see now.
also possible there is some trash in the oil galley partially blocking oil flow.not likely.
you may check the oil pump pickup for clogging.
hope it goes cheap for you.

[Crosshair Cowboy]

I am having this exact same problem. Good oil pressure at initial start up, but drops down to 7 psi at warm idle. Freshly rebuilt 350. I have tried 3 different gauges, hoping it wasn't so. They did put a new cam in it. What do you fellas think. No knocking, but I sure would feel better if it was reading at least 30-40 psi at idle.

[Custom 68]

Wow what an old thread. I mope yours isn't like mine but I did indeed wipe out a bearing or 2 still not sure what happened but it was doomed from the start on mine. I tried to do mine on the cheap and didnt check everything as good as I should have.
The good news and a few bucks later mine turned into a turbocharged gen 3 motor with a 6 speed...
good luck with yours but I have heard if it is holding some pressure at idle but goes up when you rev it up or driving it then all should be ok but yes it is disconcerning to see it that low anytime..

[GASoline71]

Almost a 9 year old thread... Draggin' the waters...

It will never read 30-40 psi at idle when warm. That's race car pressure right there.

Gary