Low Oil Pressure

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Feb 20, 2011 | 07:41 AM

Wicked Endings

Thread Starter

Elder User

Joined: Apr 2010

Posts: 645

Likes: 2

From: Richlands, NC

Low Oil Pressure

So, I have a 1985 F-150 with a 4.9 I6 carbed engine...

When I first start my truck, my oil pressure is around 50-51 where its supposed to be, however, when the truck starts to warm up, the pressure goes way down between 15-20... And when i'm sitting idling at a stop sign or light, it goes down between 5-10... Then when you give it gas it'll go back up to 15-20..

So... I'm just wondering what causes this...

I mean, the truck doesn't shudder, it doesn't try to stall or anything...

Any ideas?

Feb 20, 2011 | 09:03 AM

4x4 Bart

Fleet Mechanic

Joined: Feb 2007

Posts: 1,326

Likes: 48

From: Middle TN

Sounds like normal wear. This is enough oil pressure to lube the engine. Volume, not high pressure is what you want. If you want more pressure go to a thicker oil. As long as it doesn't go to zero at idle you're O.K. I have seen engines run for years on 10psi

Feb 20, 2011 | 11:02 AM

rikard

Posting Guru

Joined: May 2007

Posts: 1,208

Likes: 2

From: North Reading Mass

X2 on what Bart posted. Many of my engines developed the same symptoms as yours as they aged. My 83 302 went 220k and its oil pressure was similar to yours after 132k. I did use a higher viscosity oil in the summer and added an external engine oil cooler which helped bring the pressure up to about 25psi from 10 at idle. On one of my SBCs the oil pressure went up quite a bit at hot idle after replacing the cam and lifters.
regards
rikard