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JohnnyA

Oil Pressure, Demystified Please?!?!

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JohnnyA

Folks,

I'm very confused about what the correct oil pressure should be.

In my 2007 VTX with Indmar 330 engine, at idle after 10 minutes or so it reads around 45 psi. My engine's manual states "Oil Pressure at Idle" should be "4 PSI (41 kPa) Minimum Hot".

I've read a lot of posts here from other's and the consensus seems that oil pressures around 40 psi (roughly, depending on engines) is normal, ok at idle.

So why does the manual read 4 PSI Minimum? I'm certainly above the minimum so I guess it's ok? But why don't these engine manufacturers state normal operating pressures? Maybe because there's just too many fluctuation causing variables that they just reasonably can't?

Thoughts?

Thanks! 

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carguy79ta
Posted (edited)

I would guess the minimum is just that, the minimum it would take to lube the motor. 4 psi at idle would prolly be 20 psi at normal revs. If my motor suddenly went from 40 psi to 10 psi, I would think it until I found out what happened. That would indicate a clog somewhere.

Edited by carguy79ta

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Woodski

@JohnnyA- There are many factors that establish what your idle oil pressure will be including: oil viscosity and age (breakdown), engine oil temperature, bearing clearances due to age / wear, idle speed.  The manual is giving what they consider to be the minimum safe idle oil pressure when all the factors are detrimental to oil pressure level.  In your case, the oil temperature was probably not up to operating or at an elevated temperature.

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oldjeep

I'd be pretty concerned if i ever saw 4 psi.  

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Sixball

That is what I see on my same year and engine.

 

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TallRedRider

It strikes me as different that his idle PSI is over 40.  Isn't that super high for an idling engine?  

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BSUBU_Kris

If I go a full 50 hours between oil changes I loose about 10 psi at idle.  It seemed to start around 35 hours or so.  I also need to add about 3/4 quart of oil at 35 hours.  It is toward the bottom of the normal range on the dip stick when I add at 35.  I have a 2010 LSV with the Monsoon 350.  I just change my oil every 30 hours.  I have had the boat since new and intend to keep it for many more years so really cheap insurance changing the oil.  I have a 12V extraction pump, remote oil filter and can change the oil in about 15 minutes.  I just hook up the pump when I pull it out of the water.  By the time I am done wiping down the boat the oil is fully pumped out.  I refill the oil before putting it back in the garage and usually change the filter prior to putting it back in the water the next trip so it isn't hot.  You can get a gallon of Chevron Oil for less then $15 so an oil change is less then $30.

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JohnnyA

Thanks for all the info. You've put my mind at ease.

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formulaben
On 5/19/2019 at 6:47 AM, JohnnyA said:

So why does the manual read 4 PSI Minimum?

I believe it's because that's the trigger for the oil pressure switch.

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Ryan1776

Been drag racing for many years and a good rule of thumb is 10psi for every 1000 rpm....While 4psi seems low for an idle speed of approx 600-700 idle rpm, as @Woodski mentioned MANY variables go into that number. 

I used to sell high performance engine parts. I called Melling (oil pump manufacturer) and talked to one of the engineers there about that. He told me that that 10psi/1000rpm is a good safe rule, it's also pretty dated. He told me that the machining tolerances and capabilities are so good anymore that you can run less than that and be completely safe. 

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Nitrousbird
On 5/19/2019 at 9:05 AM, oldjeep said:

I'd be pretty concerned if i ever saw 4 psi.  

This.  If you are seeing 4psi (and isn't just a gauge malfunction), your motor is hosed, regardless of the "let's get it through until the warranty expires" BS Indmar prints in their manuals.

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Michigan boarder

I thought the oil pressure switch trips the alarm or shuts off the fuel pump at 5psi.

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MadMan
On ‎5‎/‎19‎/‎2019 at 3:47 PM, BSUBU_Kris said:

If I go a full 50 hours between oil changes I loose about 10 psi at idle. 

This is the reason I don't use multi-viscosity oil (10w40) and just use straight weight (40w).  The viscosity improvers shear with use making 10w40 oil more like 10w oil.  I normally don't start my boat below 60F so I don't need multi-viscosity.

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