63 390. I'm having issues with the oil pressure light coming on when the motor gets warmed up and I'm driving. as soon as the rpms drop down to a stop my light comes on. i thought oil pump must be bad. i pulled the pump cover and pulled the gears out. they looked good. no heat marks from starving oil. the cover wasn't scored badly, out the 4 i have the 1 on the motor was the best. pulled the spring and collar out and all checked good. Put it all back together with lots of jelly. used a 15 thousands thick gasket. put in a shim to bump up the psi. Drove around the hood and it still does it.if you give it gas it jumps right back up to about 23psi. i have an auto meter gauge. the problem is it reads up to 100psi so its not very accurate for the Cadillac motors. Im thinking if it where something in the pick up tube or a clogged screen it would always have psi issues? anyone have any sugestions? i believe the oil lights come on at 7 psi and the cadillac pumps top out at 25 or so psi? Im ready to just unplug the damm idiot light and just plain be an idiot!
How fresh our your main bearings? That can sometimes point to wear. Especially when it reaches operating temp.
Could be too much bearing clearance. Good oil pressure when cold and starts dropping as temp goes up? You could try a thicker weight oil like a 20w50 might keep the pressure high enough to keep the light off.
I have a late model that i was having the same problem with, its all worn out so i just thought it was the oil giving way, so i did an oil change and the problem persisted, so i wasnt sure what i was gonna do, later that day it stopped doing it and hasnt done it since (2 weeks) so i dont know what the problem was, i was gonna try and put a better quality filter on it. JEFF
im running a wix filter. 10 30w oil motor was rebuilt a few years ago, but maybe has 200 miles on it....
23psi? I'll bet its bottom end time with the rest of the best. I had a 59ranch wagon with a 292 innit and had the same issues. As a stupid kid I realized 90 wt and a product called STUD, (remember that?) motor glue and it had lotsa pressure.Then it blew and stank, I mean STANK for blocks. get the bearings and youll be fine. I had a 390 in a 63 he**** and its a *****en motor.
Sometimes on rebuilds, not always, they don't clean the block good enough and a metallic sludge can be in any number of p***ages. Can cause all kinds of problems. Hope you find the fix.
I've had good luck with a bottle of Lucas and 15w40 diesel oil, doesn't break down as fast and seems to hold pressure better in ANYTHING I have ran it in. Is it possible the sensor for the idiot light is bad? That would be my first guess. Does the pressure drop below 7psi? If not, I would say you are ok. I built a fresh Pontiac 455 a few years ago and it ran low pressure at idle but was always fine when cruising. I think it has something to do with large bearing journal surfaces in these bigger engines.
see if you can find a sending unit for the gauge that goes down to 5psi before it turns on. maybe its just teetering at the 7/6 psi, i worked on an old mopar, i just turned the idle up a tiny bit, its not the correct fix but we were about to rebuild an old slant six cause of low oil psi JEFF
Cam bearing clearance could be the problem. If it ain't makin noise take the bulb out of the light and drive it. Ya got plenty of pressure when it's needed.
Low oil pressure can be a sign of a worn motor - or a motor with lots of "little taps" turned on inside it. You've gotta find those little taps and turn them off. there are many reasons why this has happened - relief valve stuck worn rockers worn cam bearing worn main and big end bearings Or is there an oil gallery plug that has moved or deteriotated and is leaking ? Lots of options and until someone goes inside no one really knows. I had an early Poly motor that did the same thing - had a great bottom end, new oil pump however I was too scared to touch the cam bearing and the rockers and guess what - they needed doing also. Fixed the wear (turned the tap off) and voila - good oil pressure
thanks all for your replies. i think i got it, at least it was good for a short cruise around the neighborhood and a blast down some country roads. i changed out the 10 w 30 for some 20 w 50 installed a new wix filter installed a new pressure sender and it was good so far. like i said i have no noise no metallic in the oil, and the oil is like brand new when drained. I'm hoping it works, if not looks like ill be pulling a 390 motor soon or blowing her up on the way to round up!!
I was nervous about this problem too. I did a complete overhaul on my 390, minus having the crank turned. Put standard bearings back on factory crank, started it up and freaked out when the gauge read only 25psi. I was so nervous I wouldn't run it long enough to watch it possibly drop more. After hearing everyone tell me to just drive it, I did, and low and behold it runs great! The oil pressure never really moves to be honest. At idle it reads 22-25psi and running down the highway at 65mph and about 2500rpm it might be at 26-28psi. The local library had an old Chilton book on the 59-62 Cadillac engines and it listed typical pressure at 33 psi at 55mph. Wierd??
Man!!!! put a manual guage on it and T it in to your sending unit for the idiot light, that way you will know for sure what your oil pressure really is. DUH.
My 390 (all fresh and on 20/50 oil) has never run any more than 30psi stone cold and 25(ish) psi hot. Even when I spat a push rod and follower out it only dropped to 15 psi! Seems that the volume pumped is OK but the pressure seems low when compared to other motors.
just saw that there's been some activity on this so i thought id update. I've got about 2000 miles on it now and no issues. running about 30 psi and smooth as ever.
I just had my 390 out of my 61 CD rebuilt and the oil pressure is reading 25psi cold? seems to me that something is wrong? anyone know whats the problem could be.. barrings crank and everything else look perfect, has a brand new oil pump in it. im stumped?
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