Is it broken or not?

[Mikecaldo]

So I have a pretty basic question about oil pressure in my engine -- I'm hoping some of you can correct any misconceptions I've got about how this is supposed to work. My boat is almost 20 years old, Volvo Penta 5.0 GL PEFS. So, first, I'd imagine it is reasonable to assume that the gauges, wires, etc may be starting to break down with wear and tear. Here is what I've noticed: At constant throttle, moving on a calm lake in a straight line, the gauge for my oil pressure stays consistent and pegged right about in the middle. Throttle up, throttle down, bank to turn, or just hit some chop and the needle will move in a relatively inconsistent manner. At idle it stays right at the high end of the low pressure "red" zone.

So, I've got two major questions:

1- what is normal for oil pressure in a marine engine? I have no idea. I know that in my truck and my car you don't get anything near that kind of variation in pressure, but I don't think that's a real great comparison since they run on a flat consistent surface. Is that normal or not?
2- If there is some kind of an oil delivery issue (and the problem is not old cracked wires to the gauge or a worn our sending unit) would there be some kind of a change in performance or any other indication that there is a problem?

For what it's worth, the boat runs like a top. Oil level is spot on by the manual and on the dipstick. If this sounds normal to you guys I'll just leave it alone. Otherwise, it made sense to me to spend the $50 and change the sending unit and see what happens. Or to test the gauge and see if it is functioning properly.

I'd love to get someone's thoughts that can speak with some authority on this. If it helps, I did get some video on the lake last week of the tach and the pressure gauge for a few minutes doing what they do.

Thanks in advance for sharing your collective expertise.
Mike

 

[dingbat]

Erratic behavior related to motion an or vibration is a sign of a loose or corroded ground connection and/or a failing gauge(s)

 

[wrench 3]

Your idle oil pressure is nothing to worry about.
It does sound like you have a bad connection somewhere but not necessarily a ground. Try shaking the wiring and banging the gauge (carefully) to see what happens with the gauge.

 

[Mikecaldo]

Ok thanks for the input. I’m going to fiddle with it this week. So there is an oil pressure sender that looks like a bell—- that’s the one that goes to my dash gauge. And then there is a second oil pressure switch by my oil filter that sets the audible alarm. Is that correct? So in theory if oil pressure got too low that alarm would beep anyways, right?

 

[Scott Danforth]

first, stop playing with the font. your first post is a biotch to read

on an SBC there are two places the oil pressure can be read on the block. one is the port at the back of the block by the distributor (most common), the other is near the oil filter boss. and yes, the oil pressure sender is bell-shaped.

light blue wire is the oil pressure sender.

there is also an oil pressure switch that is often wired to the alarm.

standard oil pressure for a small block is minimum of 10 psi for every 1000 RPM. the stock spring in the oil pump in the pressure regulator is about a 50 psi spring. the rest is up to oil viscosity, RPM and bearing clearances.

however if your gauge is fluctuating, most likely a bad ground at the gauge, or a bad connection at the sender.

best thing to do is actually measure the oil pressure with a mechanical gauge and go from there.

 

[achris]

first, stop playing with the font. your first post is a biotch to read.

Fixed. :thumb:

 

[GA_Boater]

first, stop playing with the font. your first post is a biotch to read.

How's that, Scott?

 

[GA_Boater]

Fixed. :thumb:

It better be fixed - At least 3 of us worked on it.

 

[Scott Danforth]

thanks guys.....

 

[Mikecaldo]

Sorry about the font and size on the initial post. Not sure how I did that.

 

[Mikecaldo]

The low pressure switch by the oil filter has a single wire. My understanding is that the beeping stops when the motor runs and oil pressure (dis?)engages the switch. Oil pressure drops too low, the switch disengages, and the alarm should go off. Do I understand that correctly or is that backwards?

question 2, If I start the motor and then pull the wire should the alarm go off or does the switch have to trip to set it off?

last Question- i got a mechanical gauge. The pressure sender is going to be a SOB to access. Any reason I can’t pull the low pressure switch by the oil filter and check it there?

thanks again
mike

 

[QBhoy]

Hi
if the gauge is anything like my old VP gauge with red and green on it...then in the red at any rpm even idle, isn’t normal.