Should oil in pressure line for gauge go all the way to the gauge?

On Thu, 31 Dec 2009 08:53:46 -0600, jim <"sjedgingN0Sp"@m@mwt,net>
wrote:


>
> How did you make the leap from air is compressible to it will result in
>a falsely low gauge reading? You say that as if everyone is supposed to
>automagically see the connection.
>
It will be "falsely low" - momentarily.
This guy did a useful test of bled line versus non-bled.
http://mgaguru.com/mgtech/dash/dt104.htm

There are other examples if you care to find them.
In any case, I'd just go with an electric.
The one in my Grand Am seems responsive enough.
Interesting comment in the last paragraph about possible false
indication of oil filter drain down.
No, I'm not suggesting another Fram thread.

--Vic

Jeff Strickland wrote:
> "Ray O" > wrote in message
> ...
>> "muzician21" > wrote in message
>> ...
>>> Hooking up an oil pressure gauge, should the oil go all the way to the
>>> gauge or should there be an air buffer?
>>>
>>> Thanks
>> Are you hooking up the gauge temporarily to check oil pressure or are you
>> trying for a permanent installation in the dashboard?
>>
>> In either case, the oil needs to go all the way to the gauge unless you
>> are using an electrical sender type gauge.
>>
>
> What Ray said. And IF it's an electrical guage, the sender will be screwed
> directly into an oil galley somewhere, and the wire will go all of the way
> to the guage.
>
>
>
>
>> The downside to using a direct read gauge is that there are additional
>> potential sources of oil leaks, and leaking hot oil in the instrument
>> panel can cause burns and make a huge mess.
>
> That's an understatement ...
>
>
>
>

You could put a direct reading gauge on the engine with a light and
camera focused on it and a video screen with a big suction cup on it to
stick on the windshield. Or maybe an air gauge attached to the oil
line to measure the air pressure and compare it to the oil
pressure...... with two big suction cups to hold them, and of course a
vacuum gauge to measure the suction on the suction cups so you will know
when they are about to fall off, which would require another two gauges
and more suction cups unless they have a remote sensor.....

On Thu, 31 Dec 2009 14:13:12 -0600, FatterDumber& Happier Moe
> wrote:


>
> You could put a direct reading gauge on the engine with a light and
>camera focused on it and a video screen with a big suction cup on it to
>stick on the windshield. Or maybe an air gauge attached to the oil
>line to measure the air pressure and compare it to the oil
>pressure...... with two big suction cups to hold them, and of course a
>vacuum gauge to measure the suction on the suction cups so you will know
>when they are about to fall off, which would require another two gauges
> and more suction cups unless they have a remote sensor.....

Too complicated and expensive. Just lead an oil hose to a covered
bucket kept on the passenger seat. Another hose on the side of the
bucket near the bottom goes back to the engine.
Then you stick a meat thermometer through the cover, and a dipstick.
After a little testing to get the return hose sized right and the
temperature/bucket level calibrated right, it just a question of
checking the dipstick. Could put a sight glass on it if you like
fancy.
Anyway, you won't need a TV on the windshield then.

--Vic

"Heron McKeister" > wrote in
:

> "jim" <"sjedgingN0Sp"@m@mwt,net> wrote in message
> ...
>>
>>
>> Tegger wrote:
>> >

>> > >
>> >
>> > Air is compressible. Oil is not. Air in the line will result in a
>> > falsely low gauge reading. At least that's what happened to me many
>> > years ago when I added such a device to my car.
>>
>>
>> How did you make the leap from air is compressible to it will result
>> in a falsely low gauge reading? You say that as if everyone is
>> supposed to automagically see the connection.
>>
>>
>
>
> As his previous posts and replies have conclusively proven,
> he wouldn't pass a first year class in statics. Gawd forbid his
> next attempt to pointificate on the Navier-Stokes equations.
>
>
>



Firstly, I'd like to thank all for their friendly and good-natured replies
to my posts.

Secondly, here's the explanation:
Way, way back in the early '80s, I installed a capillary-type Auto Meter
oil pressure gauge in my '75 Corolla. There was air in the line after I
hooked it up. The gauge barely read anythng at all. I decided that the
problem was probably the air, so I made sure I bled out as much as I could
before reconnecting the line. The gauge then displayed a more normal
reading.

If the air didn't matter, then I obviously inadvertently did something else
that fixed the low reading, but mistakenly attibuted the fix to the removal
of the air.



--
Tegger

"hls" > wrote in
:

>
> "Tegger" > wrote in message
> ...
>> "hls" > wrote in
>> :
>>
>>>
>>> "dr_jeff" > wrote in message
>>>> Why would having the oil go all the way up to the gauge be a big
>>>> deal? Would there always be oil in the line?
>>>
>>> It wouldnt normally make much difference. If the line, partially
>>> filled with air,
>>> experienced heating or cooling, I guess the expansion or contraction
>>> of the air could be more of a factor than it would be with a tube
>>> filled with oil alone.
>>>
>>
>>
>> Air is compressible. Oil is not. Air in the line will result in a
>> falsely low gauge reading. At least that's what happened to me many
>> years ago when I added such a device to my car.
>>
>> --
>> Tegger
>
> The pressure is transmitted through the "fluid", both air and oil
> being fluids. You dont lose
> pressure just because the air is compressed.
>


So I've been believing a misconception these last 28 years. You, at least,
was civil in pointing this out to me.


--
Tegger

Tegger wrote:
> "Heron McKeister" > wrote in
> :
>
>> "jim" <"sjedgingN0Sp"@m@mwt,net> wrote in message
>> ...
>>>
>>> Tegger wrote:
>
>>>> Air is compressible. Oil is not. Air in the line will result in a
>>>> falsely low gauge reading. At least that's what happened to me many
>>>> years ago when I added such a device to my car.
>>>
>>> How did you make the leap from air is compressible to it will result
>>> in a falsely low gauge reading? You say that as if everyone is
>>> supposed to automagically see the connection.
>>>
>>>
>>
>> As his previous posts and replies have conclusively proven,
>> he wouldn't pass a first year class in statics. Gawd forbid his
>> next attempt to pointificate on the Navier-Stokes equations.
>>
>>
>>
>
>
>
> Firstly, I'd like to thank all for their friendly and good-natured replies
> to my posts.
>
> Secondly, here's the explanation:
> Way, way back in the early '80s, I installed a capillary-type Auto Meter
> oil pressure gauge in my '75 Corolla. There was air in the line after I
> hooked it up. The gauge barely read anythng at all. I decided that the
> problem was probably the air, so I made sure I bled out as much as I could
> before reconnecting the line. The gauge then displayed a more normal
> reading.
>
> If the air didn't matter, then I obviously inadvertently did something else
> that fixed the low reading, but mistakenly attibuted the fix to the removal
> of the air.
>
>
>
Unless there is a blockage somewhere in the line when the pump is
pumping 45lbs/square inch or whatever it is at the pump outlet that
would be 45 lbs/sq inch at the gauge. Air or no air. Any air in the
line would be compressed to 45Lbs and that's what the gauge would read.
OK that's it, this is the correct answer, I should know I made a
strong D- in physics.
Thread closed.

Vic Smith wrote:
>
> On Thu, 31 Dec 2009 08:53:46 -0600, jim <"sjedgingN0Sp"@m@mwt,net>
> wrote:
>
> >
> > How did you make the leap from air is compressible to it will result in
> >a falsely low gauge reading? You say that as if everyone is supposed to
> >automagically see the connection.
> >
> It will be "falsely low" - momentarily.
> This guy did a useful test of bled line versus non-bled.
> http://mgaguru.com/mgtech/dash/dt104.htm

It would have been more useful if it was done with more conventional oil - He
said he was doing the test with cold 20w50 oil. With 5w30 oil I would guess the
difference between air in the tube and no air would be much less noticeable.
The size of the tubing and thickness of the oil will determine how fast the
gauge responds.
Also, after the air is bled from the tube there shouldn't be any way the oil
can drain back out of the tube. If it does that probably means a tiny leak that
is too small for oil to leak out but big enough for air to leak in.

>
> There are other examples if you care to find them.
> In any case, I'd just go with an electric.

The electric gauge/sensor will have some dampening also to protect the gauge
from damage. Depending on how it is set up it could also have some small delay.

-jim

> The one in my Grand Am seems responsive enough.
> Interesting comment in the last paragraph about possible false
> indication of oil filter drain down.
> No, I'm not suggesting another Fram thread.
>
> --Vic

Vic Smith wrote:
> On Thu, 31 Dec 2009 14:13:12 -0600, FatterDumber& Happier Moe
> > wrote:
>
>
>> You could put a direct reading gauge on the engine with a light and
>> camera focused on it and a video screen with a big suction cup on it to
>> stick on the windshield. Or maybe an air gauge attached to the oil
>> line to measure the air pressure and compare it to the oil
>> pressure...... with two big suction cups to hold them, and of course a
>> vacuum gauge to measure the suction on the suction cups so you will know
>> when they are about to fall off, which would require another two gauges
>> and more suction cups unless they have a remote sensor.....
>
> Too complicated and expensive. Just lead an oil hose to a covered
> bucket kept on the passenger seat. Another hose on the side of the
> bucket near the bottom goes back to the engine.
> Then you stick a meat thermometer through the cover, and a dipstick.
> After a little testing to get the return hose sized right and the
> temperature/bucket level calibrated right, it just a question of
> checking the dipstick. Could put a sight glass on it if you like
> fancy.
> Anyway, you won't need a TV on the windshield then.
>
> --Vic
>
>
>
Would you use a Fram filter on that hose? I've heard they are just as
good as a genuine Toyota Filter.

FatterDumber& Happier Moe > wrote in
:

> Tegger wrote:

>>
>> Secondly, here's the explanation:
>> Way, way back in the early '80s, I installed a capillary-type Auto
>> Meter oil pressure gauge in my '75 Corolla. There was air in the line
>> after I hooked it up. The gauge barely read anythng at all. I decided
>> that the problem was probably the air, so I made sure I bled out as
>> much as I could before reconnecting the line. The gauge then
>> displayed a more normal reading.
>>
>> If the air didn't matter, then I obviously inadvertently did
>> something else that fixed the low reading, but mistakenly attibuted
>> the fix to the removal of the air.
>>
>>
>>
> Unless there is a blockage somewhere in the line when the pump is
> pumping 45lbs/square inch or whatever it is at the pump outlet that
> would be 45 lbs/sq inch at the gauge. Air or no air. Any air in the
> line would be compressed to 45Lbs and that's what the gauge would
> read.
> OK that's it, this is the correct answer, I should know I made a
> strong D- in physics.
> Thread closed.


<opens thread again>

That makes perfect sense, now that I've actually given this some thought.

Makes me wonder what I did wrong those 28 years ago.

<gently closes the thread once more>


--
Tegger

Tegger wrote:
> FatterDumber& Happier Moe > wrote in
> :
>
>> Tegger wrote:
>
>>> Secondly, here's the explanation:
>>> Way, way back in the early '80s, I installed a capillary-type Auto
>>> Meter oil pressure gauge in my '75 Corolla. There was air in the line
>>> after I hooked it up. The gauge barely read anythng at all. I decided
>>> that the problem was probably the air, so I made sure I bled out as
>>> much as I could before reconnecting the line. The gauge then
>>> displayed a more normal reading.
>>>
>>> If the air didn't matter, then I obviously inadvertently did
>>> something else that fixed the low reading, but mistakenly attibuted
>>> the fix to the removal of the air.
>>>
>>>
>>>
>> Unless there is a blockage somewhere in the line when the pump is
>> pumping 45lbs/square inch or whatever it is at the pump outlet that
>> would be 45 lbs/sq inch at the gauge. Air or no air. Any air in the
>> line would be compressed to 45Lbs and that's what the gauge would
>> read.
>> OK that's it, this is the correct answer, I should know I made a
>> strong D- in physics.
>> Thread closed.
>
>
> <opens thread again>
>
> That makes perfect sense, now that I've actually given this some thought.
>
> Makes me wonder what I did wrong those 28 years ago.
>
> <gently closes the thread once more>
>
>

small amount of debris in the line that plugged the little hole on the
back of the gauge, that got blown out when you bled the line?

I dunno, that's the best I can come up with on short notice

nate

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