Author Topic: Oil pressure  (Read 114 times)

Offline runnergeorge

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Oil pressure
« on: April 07, 2021, 12:46:05 PM »
Hello! I have a 75 c10 with a pretty much stock 350 engine. Iíve noticed that my oil pressure gauge shows about 30 psi while Iím driving at any speed and drops down close to the zero mark while Iím idling. I read another post on here that the general rule of thumb is about 10psi per 1000 rpms. Iím about to switch over to the pro flo EFI and I am going through the other systems of the engine to make sure it can handle the switch and I wanted to get some opinions on if I should replace my oil pump to either a high volume with standard pressure or a high volume high pressure pump. Any thoughts? Thanks in advance.

Offline bd

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Re: Oil pressure
« Reply #1 on: April 07, 2021, 01:48:29 PM »
Don't make any repairs until you verify the dash gauge indication using a mechanical oil pressure test gauge threaded into the same port currently occupied by the oil pressure sender.  What are you using for engine oil, is the oil level at the full mark of the dipstick, and how long has it been since the oil and filter were changed?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline runnergeorge

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Re: Oil pressure
« Reply #2 on: April 07, 2021, 09:27:00 PM »
Right now I am using conventional 10w-40, the oil level is just below the full mark, not enough to justify adding any oil to it, and I believe I am about ready for an oil change actually now that I think about it. I will get an oil pressure tester and test the pressure. I would imagine it would be a good idea to take a reading before and after the oil change?

Offline bd

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Re: Oil pressure
« Reply #3 on: April 07, 2021, 09:50:58 PM »
Before you drain the oil, let a drop from the end of the dipstick fall onto the pad of a clean dry finger.  Does the oil quickly track out along the finger ridges or does it remain contained in a tight well-defined circle?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline runnergeorge

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Re: Oil pressure
« Reply #4 on: April 08, 2021, 09:03:42 PM »
I just checked it and it stayed in a well-defined circle on my finger, it was also a little dirty looking. What does that show?

Offline bd

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Re: Oil pressure
« Reply #5 on: April 08, 2021, 09:21:12 PM »
It indicates that the oil is not contaminated and diluted with fuel.  It also shows that you can follow instructions.    ;D   ;)   8)

Verify the oil pressure using a mechanical test gauge as previously recommended.  If the oil pressure truly is low, you will need to determine why before installing power adders on the engine.  Unless it's been a gazillion miles since the last oil and filter change, I doubt an oil change will make any difference toward restoring pressure.  You will find that something (e.g., oil pump and/or bearings) is worn out.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline runnergeorge

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Re: Oil pressure
« Reply #6 on: April 08, 2021, 09:44:51 PM »
That brings me to my original post about the oil pressure, and to ask what PSI is too low? Like I mentioned, anytime I'm driving no matter what RPM the gauge says 30PSI but when I idle it will drop closer to 0 PSI. I will be checking with an oil pressure gauge, however I won't know what I'm looking at without some sort of guide to go by. What numbers should I be looking for? And should I use the gauge at idle and driving? (I've never done it so some instruction would be beneficial) Sorry I'm a noob at this and learning as I go.

Offline JohnnyPopper

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Re: Oil pressure
« Reply #7 on: April 08, 2021, 09:49:27 PM »
That's a pretty big swing.

High mileage engines and thin multi viscosity oil make for low oil pressure.

Consider a single viscosity oil on your next oil change and see if it raises your pressure. 30w or 40w

Of course the ultimate test is a mechanical gauge.
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Offline TexasRed

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Re: Oil pressure
« Reply #8 on: April 08, 2021, 10:12:47 PM »
It's most likely your oil pressure sending unit is malfunctioning. Especially if you don't hear funny noises.

You should check it all the areas of concern, idle and running down the road. Well, if you check at idle and it's like 30+ psi, you kind of already know it's probably the sending unit.

Offline runnergeorge

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Re: Oil pressure
« Reply #9 on: April 08, 2021, 11:07:54 PM »
No funny noises like knocking or chirping, runs pretty dang smooth. I will check the oil pressure with a manual tester and post my results. I scoured through the 74 and 75 manuals from this site and I believe I found where the oil pressure sender is, in the back of the block. Thanks for all your help and patience with newbies like me!