Dropping oil pressure?

[diggler]

I have an olds 455 I just had basically rebuilt.
Oil pressure at idle when the engine is cold is about 50psi.
Once the engine gets warm (about 180degrees), the oil pressure drops to 25psi at idle, and 40-42psi at 4000rpms. I'm using 20W50 in the motor.
Does anyone know why this is happening?
BTW, I did get the boat up to 71mph briefly just to see what it could do since the engine repairs were made.
Oh, also, I have an high volume oil pump, (don't know how old it is in it), and a 10qt Moroso oil pan on it also. In addition, after I broke the cam in, I drained all the oil and the super lube for the cam and put in new stuff. Should I go with heavier oil? Is there heavier oil?
Thanks for any input, this is driving me nuts....

[Jungle Boy]

That looks normal to me. Cooler oil has more viscosity. Do you have a oil temp gauge in your boat? In my boats, I can vary the oil pressure 5-6 psi by regulating the oil water flow. At 210°F, my pressure is about 47 psi, 180°F it's running about 52 psi (this is running 4000 - 5000 rpm). At idle, the engines run 65 psi cold and 40 psi warm. This is with small block chevs, but the same should apply to your motor. Don't worry, be happy.
JB
[ August 19, 2002, 10:21 AM: Message edited by: Jungle Boy ]

[spectra75]

According to Joe Mondello, Dr. Oldsmobile, in his OLDSMOBILE V-8 ENGINE TECHNICAL REFERENCE MANUAL, volume 1. Oil pressure less then 20psi is unsafe and not recommended to be operated. Internal inspection should be performed for defective oil pump or excessive engine clearances. Minium oil pressure should be 40psi with a high volume oil pump and oil pan, but 50-70 psi is preferable at high rpm. Also Mondello recommends the use of 10w-30, 20w-40 or 20w-50 to break in a new engine for at least 300 miles, or for 8 hours in marine use. It is recommended to use 10w-40 motor oil for normal applications and 20w-50 for racing applications in normal weather. You must have thin, free flowing oil in sever, cold weather conditions. (jet boat with water from the lake) Do not use heavy weight motor oil in your Oldsmobile engine.

[GlastronGuy]

As long as I have 10 PSI for every 1000 RPM, I don't worry.
But, I like Mondello's theory of not operating with less than 25 @ idle.

[diggler]

Thanks everyone, I feel much more confident with the engine. Looks like I'll have some more work to do over the winter on it, but at least I can finish the season on it.

[Wet Dream]

Hope this helps ease your worry.
Mine is a 455 also, 9qt pan, standard oil pump
52psi cold idle
25psi hot idle (after real hard running)
40-42 psi at 3500rpm hot.
It has been that way all summer, picked up a few psi with the amsoil 20-50, but nothing major. I run the shit out of engine and it holds up fantastically. Don't let it get to you, but just so you know, I am going with a Mondello rebuild this winter including restrictors and a high pressure pump.

[diggler]

Wet Dream:
Hope this helps ease your worry.
Don't let it get to youActually, this eases my worry the most. Thanks a lot for your message. After just dumping $1,000 and basically rebuilding the top half of the engine, I was scared of destroying the whole thing. I typically cruise at 3500rpm and on the right occasion, will get it up to 5000rpm for a second or two. Too worried about the oil pressure.
Will you be out at TPII this upcoming weekend?

[Wet Dream]

I usually cruise around 3100 to 4000. I can get her up to 4800, but that only lasts for a 5-8 second blast. I am hoping when I rebuild this engine over the winter that she will become bullet proof. I have done a little research talking with Lynn over at Mondello, and though it won't be cheap, I can turn that 455 into a healthy 500hp enigine without having to cringe everytime I get on the throttle. I was nervous as hell when I put this engine in and ran it, but as time goes on, I get used to the numbers on the gauges. I don't know about your oil pressure gauge, but mine goes into the red at 20 psi, and when the needle is at 25 on the idle, I sweat. lol. A quick blip on the throttle and she goes right back to 40+, so I just learn to deal with it. I wish I could be out there for TPII, but I live in Pennsylvania now. I used to live in Morgan Hill (San Jose area) and work in the city (SF). I miss that place. I might make an OP event sometime next year. We'll see.

[Rexone]

Your oil psi shouldn't be a problem. As long as your idling around 25 and it jumps to 40+ when you hit the throttle, it's normal. It's when it doesn't jump to the 40+ when you increase throttle that you should start to worry. Hope this helps

[Hallett19]

That is low oil pressure, mine pulls 75+ @ open throttle cold 65+ warm, and at idle cold it is @75+, warm 50+. Olds suck !! (sorry Bill)