no oil presure at idle

I have a 59-283 Chevy, when it warms up the oil pressure drops to zero. if I bring the idle up the pressure goes up. at cruising speed the pressure reads at 40 psi steady. I changed the oil and put 10-40 oil in it, with same results. what should I check next?

 

bearing clearances. may need a high volume oil pump?

 

what he said.....
mechanical or electric gauge?
sounds like the engine needs straight 40wt not 10-40

 

Sounds like your ready for a rebuild... Don't wait for the motor to freeze up on ya...

 

Try another guage. Mech. if possible. If no pressure. Pull pan. Check for worn bearings.You can sometimes get away with a set of new bearings and a high pressure pump for a season or 2. If you don't beat it.

 

Loose main bearings or a oil pump issue,like a parialy open reliefe valve. This porb just start?

 

How old is this engine? It sounds just like the 58 283 that was in an old truck I bought. I replaced it with a big block...plenty of oil pressure, but the gas gauge goes down too fast.

 

Relief valve came to mind also. Had this happen on a fresh rebuild. Bottom line, if a differant gauge test shows the same pressure readings, your gonna have to drop the pan.

 

Rebuild time..... Worn cam bearings as well as the rods and mains will kill the oil pressure exactly as described.

4TTRUK

 

Iblew out the p/rods in my 307 and put a hi vol pump,all good now!

 

double check the old gauge before you tear into anything, i've had one fail like that.

 

I have a mechanical gauge on a grease gun hose that I screw right into the engine to verify oil pressure. I have got a lot of miles from old Fords that had no oil pressure at idle, just depends on how hard you drive it. And fwiw, I have seen sbc engines with the rid bearings pounded completely out on one throw and still have good oil pressure so I figure it really isn't directly related to rod bearings, I'd be more likely to suspect cam bearings.

 

the engine was rebuilt in the mid 80's very low mileage on the motor, and has never been driven hard. oil pressure has always been 40 psi at speed and would drop to 15-20 psi at idle. just recently it has started to drop to 0 at idle. guess I should check the gauge first as its a a electric unit. also it only drops to 0 after it warms up. when first running even at idle its 20 psi.

 

I have seen this caused by rtv in the pick up tube screen also leak between pick up tube and block

 

ok I have replaced the pressure gauge with a mech one, at start up im seeing 42 psi, letting it idle for about 20 minutes i am seeing about 27 psi. I took it out for a ride and pressure was at 40 psi at cruising speed. at a stop idling it dropped to 25 psi. after awhile motor warmer water temp about 130 degrees the pressure drops to about 5 psi at idle. once revved or moving pressure comes up and I saw it running around 35 plus psi.
so what are your thoughts and my next step? possibly the oil pump or am I grabbing at straws? do you think it sounds like bearings or if it was bearings the pressure would always be low?

 

Is the oil in good condition, changed recently, etc?

No other changes to the engine?

 

What is your idle speed? 25 psi @ idle is fine. 40 psi at cruise is ok also.

 

Yup! Can you drop the oil pan and have a looky look inside?

 

oil and filter where the first thing I changed. I am running 10-40 in it right now.
big chuck I agree the 25 and 40 are good, its when it warms up that pressure begins to drop off. 5 psi seems low at idle and if I run it warmers im afraid that at idle it drop more. 35- 40 psi all day long at cruising speed.

 

Seems strange that it would only happen when it warms up....generally when something plugs it, it plugs it all the time.

 

if I drop the pan should I just change the oil pump? if I dont see the pick up tube off or real evidence of a clogged screen then what? also why the good presure at speed?

 

I had the same thing in a 455 olds,it was the oil pump. Makes sense that it only happens when the oil warms up, it's less "thick" when hot

 

squirrel, I agree and again when it first starts up pressures look good. in fact I let it sit and just idle and the pressure didn't drop below 35 psi. but once running down the road it drops lower. could my idle rpm be just slightly on the low side causing the oil pressure to drop?

 

If you put an idiot light in and remove the gage, you'll fix it

Could be that the oil pump is worn, but I'd be concerned about the sudden change, there could be something more serious going on.

 

when you say more serious you mean possibly worn bearings?

 

Hey Squirrel, I have a stupid question; is it possible that the oil pump drive bevel is worn? At lower rpm there isn't enough stiction to turn the pump enough? Stupid question, so go easy on me.

 

If that were the case, it would more likely be slipping as the engine revs up, or when it's cold...and there's more load on it.

Yeah, more serious like bearings, or possibly something in the cam/lifter area, or even a plug leaking.

 

Yep, makes sense.

 

when you say a leaking plug, do you mean a spark plug? over all the engine seems to be running good. should I check the compression? or drop the pan and check / replace the oil pump?

 

I had the same issue the engine had about 1000 miles on it and the pick tube came off pull the pan and check. i wish i had.