Oil Pressure question.........

[ironman24]

Hi all,
   I have a question about Oil pressure>  I have a 67 with a 350 in it.  When i start it up the pressure goes up to 40psi.  While im driving at highway speeds 50 to 60  its right around 40psi.  but if i come to a light it drops down to between 25 and 30psi.  Then back up to speed and its back up to 40psi again.  When i get to where im going and put it in park,  it drops to 25psi.  If parked and i rev the engine up it will go back up to 40psi,  but at idle it stays around 25psi.
I guess my question is............ Is this ok?  Is 25psi at idle to low?  what would cause this?
I got the car in May.  It has done this since the day i drove it home.  I changed the oil a few days after i got it.  Oil looked clean like it was just changed.  I drove it about 500 miles and changed oil again just to see how it looked.  Now its got about another 500 miles on it since that last oil change.

thanks,
Charlie

[Ed Bertrand]

Charlie you're fine. With these older Chevrolet engines, the minimum spec is 1 PSI for every 100 RPM the engine turns, or 10 PSI for every 1000 RPM the engine turns. So... if you're idling at 700 RPM, you only need 7 PSI. Going down the highway at 3000 RPM, you need 30 PSI. I like to see double that in the real world, but it's not a requirement.

Ed

[ironman24]

Ed,
  Thanks!  that info makes me feel a little better.
Charlie

[mrdetails]

How about when you're twistin' her up to about 8200 grabin for 3rd gear?

[jdv69z]

I think that there is a maximum pressure that you want as well, maybe 60-70 psi, even when you are accelerating at high RPM. Too much can be as detrimental as not enough. Jerry Mac shifts his engine at 8200 RPM when racing, so he ought to know what works.
Jimmy V.

[1968RSZ28]

How about when you're twistin' her up to about 8200 grabin for 3rd gear?

You must have a 302!   

Paul

[dutch]

I think that there is a maximum pressure that you want as well, maybe 60-70 psi, even when you are accelerating at high RPM. Too much can be as detrimental as not enough. Jerry Mac shifts his engine at 8200 RPM when racing, so he ought to know what works.
Jimmy V.

Most people think they need big pressure and volume and opt for the big block style pumps only to find they either pump too much oil into the upper end and oversaturate everything and/or suck the pan dry (if its a regular OEM style pan) and end up with really big problems. All a big pump with volume and pressure increases does is eat up HP trying to spin it while creating other oiling 'overkill' problems.
My 302 gets about 65psi when running over at 3000 rpm or over and idles hot at about 40-45psi and its just a regular volume (albeit higher pressure) Z28-style aftermarket Speed Pro version (which I think means it only has a slightly different pressure spring installed) and I consider it all or more than that or any other similar engine should ever need.
I have read stories where high winding small blocks are drag raced with setups where the engine basically runs out of light grade oil in the pan at the same point it finishes the quarter mile run - essentially ending with 0 psi oil pressure and the engine lives quite well for years. Sounded like a pretty dicey way to run an engine to me, but users assume they are saving horsepower by using as light an oil and as small a volume as possible... Apparently the oil film left is sufficient for a few seconds of low engine speed operation until the oil gathers back in the pan in the shutdown area past the finsih line - but it does demonstrate that not a lot of pressure or volume is required to make a small block live at moderate engine speeds obviously - Randy

[ss68396]

I also have a question regarding Oil Pressure...

On Friday night I took the car out to the usual meet and eveything was fine. I started it up and let it idle to warm up for 10mins. I then went to the meet and hung out for a little while. After leaving the show the car had almost 60psi on start up. While driving the pressure dropped to around 30psi. I had to make a stop at the store and that is when the pressure dropped to ZERO. The motor sounded like it was knocking. I kicked the throttle to bring the idle up higher and then the pressure resumed and the sound disappeared.

Now what would have caused this? I talked to a few fellows and their suggestion is that as the motor warms up the clearances increase and the oil is getting by casuing the pressure to drop. They recommended using a heavier weight oil and see if this corrects the problem. Currently I have 10w30 in the 454 so I will try a 20w50 which I was running in the 396 and see if this help.

Any help on this would be great.

Thanks Jay

[JohnZ]

If the pressure dropped to zero and you heard a knocking sound, you have a problem that more viscous oil isn't going to solve. Assuming you're not low on oil, the oil pump and pickup need looking at.

[rich69rs]

If the pressure dropped to zero and you heard a knocking sound, you have a problem that more viscous oil isn't going to solve. Assuming you're not low on oil, the oil pump and pickup need looking at.

....and continued running is only going to make the problem worse.  It isn't going to fix itself.  Matter of fact, if you have an oil pickup problem at the pump (partially plugged screen for example) a more viscous oil is only going to make matters worse.

[jdv69z]

Sounds like momentary oil starvation to me. Low on oil?

Jimmy V.

[ss68396]

The car was not low on oil. The dipstick read almost to the full mark. I am having a slightly larger leak than usual from around the filter. I did change out the filter yesterday and the leak still seems to be there. It is tough to see under there due to the headers but I will get a better look hopefully tonight.

I did change the oil and there was no large particles or debris. Would you guys suggest dropping the pan and replacing or cleaning out the pump??