ok, so here’s a question (a few, actually):
what, exactly, is the oil pressure gauge on our 90 Miata
trying to tell us- and, what is a ‘normal’ reading?
Is the pressure level an indication of the presence or
absence of a sufficient amount of engine oil, or does it
have some deeper meaning, like something to do with compression?
i assume there must be something to it, beyond its ‘cool factor
quotient’. why did they decontent this out of the later cars,
anyway? penny-pinching?
FWIW, on a cold (40 degrees F, this is florida) morning,
before the car warms up, it will indicate 60+. While warm,
at idle, it will hover below the 30 lb/in2 mark, and underway,
it generally sits at the 12 noon position (30+). this is the original
engine with more than 120K miles on it [and it seems to be
running _perfectly_ 
]. thanks for any input/suggestions…
In article <69j4gc$…@bgtnsc02.worldnet.att.net>, nowhere…@nowhere.net
(jimmy mcgruger) wrote:
>Is the pressure level an indication of the presence or
>absence of a sufficient amount of engine oil, or does it
>have some deeper meaning, like something to do with compression?
>i assume there must be something to it, beyond its ‘cool factor
>quotient’. why did they decontent this out of the later cars,
>anyway? penny-pinching?
It’s the pressure in psi (US models) in the oil system. Too-low pressure
could mean you’re low on oil, or it could mean your main bearings are
worn. Too-high pressure usually indicates a clogged oil passage. Zero
pressure means SHUT IT OFF IMMEDIATELY. That’s why the gauge is on top,
where you can see it easily.
>FWIW, on a cold (40 degrees F, this is florida) morning,
]. thanks for any input/suggestions…
>before the car warms up, it will indicate 60+. While warm,
>at idle, it will hover below the 30 lb/in2 mark, and underway,
>it generally sits at the 12 noon position (30+). this is the original
>engine with more than 120K miles on it [and it seems to be
>running _perfectly_
Sounds about right. My readings, which are well within factory spec:
Cold idle: 60 psi
Cold 4000 rpm: 85 psi
Hot idle: 25 psi
Hot 4000 rpm: 55 psi
The pressures drop as the oil warms and thins out. It’s not a good idea to
use high rpm (>5000?) before the oil warms up. In cold weather, the
coolant will reach operating temperature before the oil does, so you’ll
get heat before it’s safe to start redlining the engine.
–
—
Lanny Chambers (la…@derived.com) St. Louis, USA
Visit the Hummingbird Page: <http://www.derived.com/hummers/>
I agree that your running values are about the norm. I also agree with the
othe reply posts about the high, low and zero reading significance. I
would add that a FLUCTUATING reading should alert you to an impending pump
failure.
So why have the guage? If you are going to use your new toy (what other
reason is there to have it?) then it’s good to know whats happening with
the most precious fluid in its system.
Good luck (I have a ’90 with 146,000 on it — runs great, love the gauges)
jimmy mcgruger <nowhere…@nowhere.net> wrote in article
<69j4gc$…@bgtnsc02.worldnet.att.net>…
- Hide quoted text — Show quoted text -
> ok, so here’s a question (a few, actually):
> what, exactly, is the oil pressure gauge on our 90 Miata
> trying to tell us- and, what is a ‘normal’ reading?
In article <69jm6e$…@bgtnsc01.worldnet.att.net>, WMU…@worldnet.att.net
says…
>I agree that your running values are about the norm. I also agree with the
>othe reply posts about the high, low and zero reading significance. I
>would add that a FLUCTUATING reading should alert you to an impending pump
>failure.
>So why have the guage? If you are going to use your new toy (what other
>reason is there to have it?) then it’s good to know whats happening with
>the most precious fluid in its system.
>Good luck (I have a ’90 with 146,000 on it — runs great, love the gauges)
Wish I had a gauge, instead of an idiot light in gauge clothing…
—
-=Stu=-
To E-mail a response to this post, please select the E-mail link at my
website.
Visit my non-commercial "all about wheelchairs" website at:
http://www.seflin.org/wheels
- Hide quoted text — Show quoted text -
nowhere…@nowhere.net (jimmy mcgruger) writes:
>ok, so here’s a question (a few, actually):
>what, exactly, is the oil pressure gauge on our 90 Miata
>trying to tell us- and, what is a ‘normal’ reading?
>Is the pressure level an indication of the presence or
>absence of a sufficient amount of engine oil, or does it
>have some deeper meaning, like something to do with compression?
>i assume there must be something to it, beyond its ‘cool factor
>quotient’. why did they decontent this out of the later cars,
>anyway? penny-pinching?
>FWIW, on a cold (40 degrees F, this is florida) morning,
].
>before the car warms up, it will indicate 60+. While warm,
>at idle, it will hover below the 30 lb/in2 mark, and underway,
>it generally sits at the 12 noon position (30+). this is the original
>engine with more than 120K miles on it [and it seems to be
>running _perfectly_
Given your oil pressure gauge indications, the car is in fine
shape. Same as my ’93 at 60k.
All they did in the couple of years where it was
"decontented" was change from a real sensor to more of an
"all or nothing idiot needle". These can be changed around
to the real thing (miata.net tech under-the-hood has documentation).
Oil pressure mostly varies with rpm, but the gauge is prominently
located as an allusion to competitive intent. In competition, this
is a "state of the engine" indicator – if it’s going down, you
know you’ve got a problem that isn’t getting better, and it’s
just a matter of time before you will be out of the race or should
pit for some sort of service. I suppose this would be most
useful in 24-hours or longer events where such service might be
the difference between having a finish or not.
For the ordinary driver, just pull over when you see the oil spraying
out from under the hood, as someone forgot to put the oil cap back
on. If you continue driving through the oil spray, the gauge will
eventually indicate lack of pressure, but from reports seen here,
you can pull over upon seeing the oil, and avoid having dumped enough
overboard to cause pressure drop. So, it’s mostly useless, mostly.
But it looks cool.
Oh, and Porsche makes a point of having the tach & oil pressure
be the most prominent gauges. Kinda makes the Miata more like
that, maybe.
Personally, I prefer a voltage indicator before oil pressure, but
knowing volts is far too rooted in mundane everyday existence for
fun sports machines like the Miata. It’s not like we use them
every day or anything…(25k miles/year – weekends only, right?)
In a race car, you might be using mags for ignition (and no other
electrics), and the loss of an oil cooler hose requires the driver
at least know about it immediately. In the real world, the Miata
doesn’t come with an oil cooler, but knowing that the alternator
has dropped off line might be nice.
- Hide quoted text — Show quoted text -
reu…@REMOVETHIStexas.net (Azzy) wrote:
>Stu Portner wrote:
>> In article <69jm6e$…@bgtnsc01.worldnet.att.net>, WMU…@worldnet.att.net
>> says…
>> >I agree that your running values are about the norm. I also agree with the
>> >othe reply posts about the high, low and zero reading significance. I
>> >would add that a FLUCTUATING reading should alert you to an impending pump
>> >failure.
>> >So why have the guage? If you are going to use your new toy (what other
>> >reason is there to have it?) then it’s good to know whats happening with
>> >the most precious fluid in its system.
>> >Good luck (I have a ’90 with 146,000 on it — runs great, love the gauges)
>> Wish I had a gauge, instead of an idiot light in gauge clothing…
>I’ve heard people say that simply replacing this guage with a pre-94
>gauge, as well as replacing the oil pressure sending unit, will give one
>a ‘real gauge’. Will anyone verify this? Where does one go to procure
>one of these gauge/sending units?
See my web page or miata.net (They are cross-referenced.)
Leon
Leon van Dommelen I am not responsible for what I say.
http://www.eng.fsu.edu/~dommelen White 1996 PEP Sebring Miata: Bozo.
domme…@Zmiata.net Remove the "Z"s from my e-mail address.
nowhere…@nowhere.net (jimmy mcgruger) writes:
>what, exactly, is the oil pressure gauge on our 90 Miata
>trying to tell us- and, what is a ‘normal’ reading?
It is actually telling you the pressure, as hard as that might
be to believe. And your readings are normal.
>Is the pressure level an indication of the presence or
>absence of a sufficient amount of engine oil, …
Indirectly. No oil to pump, no pressure. AFAIK, if the bottom
drops out of your motor during a hill climb, you will see the
pressure drop to zero and (if you notice it) may be able to
shut down in time. In contrast, the engine temperature does
not tell you if there is any water in the cooling system and
will not (I am told) read true if you dump all the water.
> … or does it
>have some deeper meaning, like something to do with compression?
A gearhead will have to answer this, but I think you notice
bad rings in performance long before you see a pressure drop.
It would take a lot of oil going to the wrong place for that
to be visible on a gauge.
The detail is that oil viscosity changes with temperature, so
less pressure is used to push the oil through the engine. The
pressure also changes with rpm. As a result, "normal" is not
a constant value (and not described in the manual).
>i assume there must be something to it, beyond its ‘cool factor
>quotient’. why did they decontent this out of the later cars,
>anyway? penny-pinching?
They were tired of answering questions like yours. ;-) And mine.
I asked a tech that one during its first checkup. The tech said
the numbers are not calibrated absolutely, but you should monitor
relative changes.
>FWIW, on a cold (40 degrees F, this is florida) morning,
>before the car warms up, it will indicate 60+. While warm,
>at idle, it will hover below the 30 lb/in2 mark, and underway,
>it generally sits at the 12 noon position (30+).
Sounds right to me.
–
James A. Carr <j…@scri.fsu.edu> | Commercial e-mail is _NOT_
http://www.scri.fsu.edu/~jac/ | desired to this or any address
Supercomputer Computations Res. Inst. | that resolves to my account
Florida State, Tallahassee FL 32306 | for any reason at any time.
reu…@REMOVETHIStexas.net (Azzy) wrote:
>I’ve heard people say that simply replacing this guage with a pre-94
>gauge, as well as replacing the oil pressure sending unit, will give one
>a ‘real gauge’. Will anyone verify this? Where does one go to procure
>one of these gauge/sending units?
I’ve got a ’96 that *had* the ‘analog idiot light’ gauge. I spent about $150 at
Roebuck and an hour or so in my garage and now I have a *real* gauge. It was
absolutely worth it as far as I’m concerned. The installation
would have been shorter but I spent a lot of time figuring out how to get the
instrument cluster out without breaking anything. There are a couple of
writeups that were very helpful at
http://www.miata.net/garage/opg.html
I’m all thumbs at mechanical work so if I can accomplish this, I’m sure anyone
else can.
- Hide quoted text — Show quoted text -
>–
>Azzy
>’97 STO Twilight Blue "Maggie" (SW Austin, TX)
>vroom! _-n__\___
>__________`(o)–(o)/________________
jimmy mcgruger <nowhere…@nowhere.net> wrote in article
<69j4gc$…@bgtnsc02.worldnet.att.net>…
> ok, so here’s a question (a few, actually):
> what, exactly, is the oil pressure gauge on our 90 Miata
> trying to tell us- and, what is a ‘normal’ reading?
FWIW, I have two 90′s. One runs abut 45 psi (halfway between the 30 & 60)
at 4,000 rpm, and idles at an indicated 25 psi. The second car (with 20k
fewer miles) runs at about 35 psi @ 4000 rpm, & idles at something like 10
psi.
I don’t know if this is an actual variance in oil pressure, or if the
guages/senders in the two cars are off that much, one to the other. One of
these days I would like to stick a temporary mechanical guage on each car
to answer that question, but in the meantime, I think I’ll have a beer.
HP