Time to "Slay the myths again" What is the NORMAL oil pressure

[thomas g. warner]

I don't know about anyone else but I am SURE fixated on my coach oil
pressure and 10# at idle is a problem IF it is a good reading. Oil pressure
is the number one thing I watch and water temperature is #2. I even intend
to put audible sensors on both of them and on engine and tranny oil temp also.

Low oil pressure is THE NUMBER ONE killer of the olds 455 engine bottom end
. Thats why Mondello puts oil resticters in 2,3 and 4 main bearing oil gally
holes leading to the cam bearings. Keep the oil pressure in the bottom at
least 20 Remember the 455 has huge main bearings and needs a large volume
of oil. Thats why many of you have low oil pressure. You are using to light
an oil. You should be using 10W-30, 10W-40 or 20W-50 oils depending on your
oil pressure at idle. Look at your maintenance manuals, light or diluted
oil causes low oil or erratic pressures, and thick oil causes high oil
pressures. Use a 20W-50 weight oil in your engine below 30 degrees and you
will probably blow it clean off the block.

Here is the partial technical note on page 41 of his technical notes for
the 455

"Oil pressure less than 20# is unsafe and not recommended to be operated.
Internal inspection should be performed for defective oil pump or excessive
engine clearances. minimum oil pressure should be 40 PSi with a high volume oil.

If your engine has been rebuilt chances are it was by a machinest that does
mostly chevy engines. they often leave out the rear left oil gally plug and
if so you will have low oil pressure.

Bottom line. Select a weight of oil that gives you good oil pressure. Be
careful however when temperatures get below 30 degrees F.

As Arch says "thats what I do'


>Don't be too fixated on oil pressure. If you go to a higher weight oil to
>increase pressure, all you have really achieved is reducing flow. Dick
>Paterson had some good comments concerning oil pressure and flow at Marion -
>I wish I had taken better notes.
>

>
>> In my opinion 23-25 # of oil pressure should be at idle if you want an
>> engine that is going to last. 23-25# at 2450 RPM you are asking for
>> trouble. I will bet that you are using a 10W-30 oil in your engine.
>>

>> >
>> >>10# at idle is ok and 10# per 1000 rpm is the rule of thumb.
>> >>J.R.
>> >>
>> >That's good news... then my 23-25lbs at 2450 in the hot
>> desert ain't so bad.
>> >
>> >Heinz
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach
"The beautiful Mohawk Vally"

 

[robert hopper]

I have had low oil pressure on my 74 Elaganza since I purchased it. The
previous owner said it was normal. Well needless to say, 20 K miles later
I'm paying for Golby to rebuild it.
- -----Original Message-----
From: Thomas G. Warner
To: gmcmotorhome
Date: Thursday, April 29, 1999 8:45 PM
Subject: RE: GMC: Time to "Slay the myths again" What is the NORMAL oil
pressure

>I don't know about anyone else but I am SURE fixated on my coach oil
>pressure and 10# at idle is a problem IF it is a good reading. Oil
pressure
>is the number one thing I watch and water temperature is #2. I even intend
>to put audible sensors on both of them and on engine and tranny oil temp
also.
>
>Low oil pressure is THE NUMBER ONE killer of the olds 455 engine bottom end
>. Thats why Mondello puts oil resticters in 2,3 and 4 main bearing oil
gally
>holes leading to the cam bearings. Keep the oil pressure in the bottom at
>least 20 Remember the 455 has huge main bearings and needs a large volume
>of oil. Thats why many of you have low oil pressure. You are using to
light
>an oil. You should be using 10W-30, 10W-40 or 20W-50 oils depending on your
>oil pressure at idle. Look at your maintenance manuals, light or diluted
>oil causes low oil or erratic pressures, and thick oil causes high oil
>pressures. Use a 20W-50 weight oil in your engine below 30 degrees and you
>will probably blow it clean off the block.
>
> Here is the partial technical note on page 41 of his technical notes for
>the 455
>
>"Oil pressure less than 20# is unsafe and not recommended to be operated.
>Internal inspection should be performed for defective oil pump or excessive
>engine clearances. minimum oil pressure should be 40 PSi with a high volume
oil.
>
>If your engine has been rebuilt chances are it was by a machinest that does
>mostly chevy engines. they often leave out the rear left oil gally plug
and
>if so you will have low oil pressure.
>
>Bottom line. Select a weight of oil that gives you good oil pressure. Be
>careful however when temperatures get below 30 degrees F.
>
>As Arch says "thats what I do'
>
>
>

>>Don't be too fixated on oil pressure. If you go to a higher weight oil to
>>increase pressure, all you have really achieved is reducing flow. Dick
>>Paterson had some good comments concerning oil pressure and flow at
Marion -
>>I wish I had taken better notes.
>>

>>
>>> In my opinion 23-25 # of oil pressure should be at idle if you want an
>>> engine that is going to last. 23-25# at 2450 RPM you are asking for
>>> trouble. I will bet that you are using a 10W-30 oil in your engine.
>>>

>>> >
>>> >>10# at idle is ok and 10# per 1000 rpm is the rule of thumb.
>>> >>J.R.
>>> >>
>>> >That's good news... then my 23-25lbs at 2450 in the hot
>>> desert ain't so bad.
>>> >
>>> >Heinz
>>
>>
>Tom & Marg Warner
>Vernon Center NY
>1976 palmbeach
>"The beautiful Mohawk Vally"
>

 

[patrick flowers]

>
> Low oil pressure is THE NUMBER ONE killer of the olds 455 engine bottom end
> . Thats why Mondello puts oil resticters in 2,3 and 4 main bearing oil gally
> holes leading to the cam bearings.

Actually, the restrictors are to keep too much oil from being pumped
onto the engine top end. We discussed this several months back - the
oil accumulates up top quicker than it can drain back down. Not usually
a problem with low rpm motorhome motors.

> Keep the oil pressure in the bottom at least 20 Remember the 455 has
> huge main bearings and needs a large volume of oil.

That's right, high volume - not high pressure. Think for a minute why
the pressure goes up when you use a heavier weight oil. Oil pumps are
positive displacement gear-type pumps. The pump moves the same amount
of oil regardless of its weight(there is some increased efficiency with
heavier oil, but that's not where most of the additional pressure comes
from). There are only two ways to increase pressure - increase pump
speed or reduce flow. That's why you can blow a filter apart in cold
weather. The pump is gonna move the oil - a positive displace pump has
no other choice(that's why it's called a positive displacement pump as
opposed to a centrigual pump, which has a "churn" or maximum pressure).
The oil is too thick to move through the galleys fast enough, so the
pressure skyrockets.

> Here is the partial technical note on page 41 of his technical notes for
> the 455
>
> "Oil pressure less than 20# is unsafe and not recommended to be operated.
> Internal inspection should be performed for defective oil pump or excessive
> engine clearances. minimum oil pressure should be 40 PSi with a high volume oil.

20psi at what rpm? Joe has lots of good ideas and lots of good stuff
for Olds motors, but the vast majority of his work goes into high
performance or race applications. Need to keep that in mind when
reading his stuff.

Patrick
- --
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[patrick flowers]

>
> I have had low oil pressure on my 74 Elaganza since I purchased it. The
> previous owner said it was normal. Well needless to say, 20 K miles later
> I'm paying for Golby to rebuild it.

Robert,

Could you be more specific about your "low oil pressure"? What was the
pressure at what rpm?

Patrick
- --
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[robert hopper]

I am up in the air on what oil pressure I really had. My dash mounted gauge
was pegged. The previous owner had an auxiliary gauge installed, but I was
told that it wasn't accurate. I found it was leading oil which I corrected.
When at idle this gauge was bouncing around 10 AT about 55mph, it would go
up to about 15 or 20
- -----Original Message-----
From: Patrick Flowers
To: gmcmotorhome
Date: Thursday, April 29, 1999 9:37 PM
Subject: Re: GMC: Time to "Slay the myths again" What is the NORMAL oil
pressure

>>
>> I have had low oil pressure on my 74 Elaganza since I purchased it. The
>> previous owner said it was normal. Well needless to say, 20 K miles later
>> I'm paying for Golby to rebuild it.
>
>Robert,
>
>Could you be more specific about your "low oil pressure"? What was the
>pressure at what rpm?
>
>Patrick
>--
>Patrick Flowers
>Mailtoatrick
>
>The GMC Motorhome Page
>http://www.gmcmotorhome.com
>

 

[patrick flowers]

>
> I am up in the air on what oil pressure I really had. My dash mounted gauge
> was pegged. The previous owner had an auxiliary gauge installed, but I was
> told that it wasn't accurate. I found it was leading oil which I corrected.
> When at idle this gauge was bouncing around 10 AT about 55mph, it would go
> up to about 15 or 20

Thanks Robert! Assuming the gauge was accurate, the 20psi at speed is
too low.

Patrick
- --
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[richard waters]

Patrick,
Now, I'm not an engineer, just a computer sales guy. But, I was kind of
wondering why you would want to make the oil thicker, by increasing
its viscosity, in order to raise the pressure. Like you said, the oil in a
positive displacement pump is going to move the same volume,
for the most part, regardless of viscosity. So why adjust the viscosity in
order to come up with a desired pressure?

At any rate, I'm in big trouble with my engine if I am supposed to get the
numbers that Joe recommends. The only time I see 40 lbs pressure is when
I'm doing 65-70 MPH. The rest of the time I'm down near 15 lbs at idle.
If I'm supposed to have 40 at idle, I guess I better plan on a new engine soon.

Richard Waters '76 PB, Troy, with 130,000 miles on the original engine

> That's right, high volume - not high pressure. Think for a minute why
> the pressure goes up when you use a heavier weight oil. Oil pumps are
> positive displacement gear-type pumps. The pump moves the same amount
> of oil regardless of its weight(there is some increased efficiency with
> heavier oil, but that's not where most of the additional pressure comes
> from). There are only two ways to increase pressure - increase pump
> speed or reduce flow. That's why you can blow a filter apart in cold
> weather. The pump is gonna move the oil - a positive displace pump has
> no other choice(that's why it's called a positive displacement pump as
> opposed to a centrigual pump, which has a "churn" or maximum pressure).
> The oil is too thick to move through the galleys fast enough, so the
> pressure skyrockets.
>
> > "Oil pressure less than 20# is unsafe and not recommended to be operated.
> > Internal inspection should be performed for defective oil pump or excessive
> > engine clearances. minimum oil pressure should be 40 PSi with a high volume oil.
>
> 20psi at what rpm? Joe has lots of good ideas and lots of good stuff
> for Olds motors, but the vast majority of his work goes into high
> performance or race applications. Need to keep that in mind when
> reading his stuff.
>
> Patrick
> --
> Patrick Flowers
> Mailtoatrick
>
> The GMC Motorhome Page
> http://www.gmcmotorhome.com

 

[heinz wittenbecher]

Richard,
You're probably doing ok.

If you're getting 10 at idle and 30/40 at cruise it's probably better than
the book (gmc) says it should be. Don't get confused by 'modified' as the
case with a Mondello engine. That's not to say it shouldn't be that way for
a Mondello, but lets not compare apple to oranges or get concerned, possibly
unnessesarily.

For my own 2 cents I'm going to monitor for change rather than actual. we
can (or at least I can) fret ourselves into a frenzy simply trusting a gauge
too much. I have a mechanical that doesn't 'dip' like my digital does. The
digital has dipped to as little as 4 lbs momentarily on decelaration...
something the mechanical never got close to

Fun and games....

Heinz

- -----Original Message-----
From: Richard Waters
To: gmcmotorhome
Date: Thursday, April 29, 1999 7:24 PM
Subject: Re: GMC: Time to "Slay the myths again" What is the NORMAL oil
pressure

>Patrick,
>Now, I'm not an engineer, just a computer sales guy. But, I was kind of
>wondering why you would want to make the oil thicker, by increasing
>its viscosity, in order to raise the pressure. Like you said, the oil in a
>positive displacement pump is going to move the same volume,
>for the most part, regardless of viscosity. So why adjust the viscosity in
>order to come up with a desired pressure?
>
>At any rate, I'm in big trouble with my engine if I am supposed to get the
>numbers that Joe recommends. The only time I see 40 lbs pressure is when
>I'm doing 65-70 MPH. The rest of the time I'm down near 15 lbs at idle.
>If I'm supposed to have 40 at idle, I guess I better plan on a new engine
soon.
>
>Richard Waters '76 PB, Troy, with 130,000 miles on the original engine
>

>

>> That's right, high volume - not high pressure. Think for a minute why
>> the pressure goes up when you use a heavier weight oil. Oil pumps are
>> positive displacement gear-type pumps. The pump moves the same amount
>> of oil regardless of its weight(there is some increased efficiency with
>> heavier oil, but that's not where most of the additional pressure comes
>> from). There are only two ways to increase pressure - increase pump
>> speed or reduce flow. That's why you can blow a filter apart in cold
>> weather. The pump is gonna move the oil - a positive displace pump has
>> no other choice(that's why it's called a positive displacement pump as
>> opposed to a centrigual pump, which has a "churn" or maximum pressure).
>> The oil is too thick to move through the galleys fast enough, so the
>> pressure skyrockets.
>>
>> > "Oil pressure less than 20# is unsafe and not recommended to be
operated.
>> > Internal inspection should be performed for defective oil pump or
excessive
>> > engine clearances. minimum oil pressure should be 40 PSi with a high
volume oil.
>>
>> 20psi at what rpm? Joe has lots of good ideas and lots of good stuff
>> for Olds motors, but the vast majority of his work goes into high
>> performance or race applications. Need to keep that in mind when
>> reading his stuff.
>>
>> Patrick
>> --
>> Patrick Flowers
>> Mailtoatrick
>>
>> The GMC Motorhome Page
>> http://www.gmcmotorhome.com
>
>

 

[donald w. miller]

I must need to be enlightened. Sometimes I get "fixated" on the gals
passing by, but never on my oil pressure gauge.

Probably this is because I don't think low oil pressure alone is a serious
problem unless it is so low there is metal to metal contact in the engine
internals due to oil starvation.

Isn't most of the protection provided by the oil film itself ? I thought
the advantages of a pressure oiling system is more oil moves through the
bearing surfaces for improved cooling and there is more even oil
distribution.

Am I overlooking another 455 killer lurking in this low oil pressure arena
other than metal to metal contact ?

Low oil pressure often indicates a high time engine nearing overhaul but
that is a different matter altogether.

Lower oil pressure has some advantages as long as there is enough pressure
to move oil to all parts of the engine where it is needed.

With lower pressure less heat is generated and less horsepower is needed to
turn the oil pump. The engine is somewhat more efficient, less heat is lost
through the radiator, better fuel mileage, etc.

With multi viscosity oil, both dinosaur and synthetic, my rule is use the
thinnest oil a particular motor tolerates well. When it starts to burn the
thin stuff too fast I change to a thicker grade to improve the oil mileage.
I use this rule with multiviscosity oil in all water cooled and pressure
oiled engines.

I guess this makes me somewhat a contrarian but this simple rule has worked
well over the years with a wide variety of gas and diesel equipment.

Don Miller
75 Glennbrook
Shenandoah Valley

> I don't know about anyone else but I am SURE fixated on my coach oil
> pressure and 10# at idle is a problem IF it is a good reading. Oil
pressure
> is the number one thing I watch and water temperature is #2. I even
intend
> to put audible sensors on both of them and on engine and tranny oil temp
also.
>
> Low oil pressure is THE NUMBER ONE killer of the olds 455 engine bottom
end