Mechanical Oil Pressure Gauge, - does it need to be bled? |
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Mechanical Oil Pressure Gauge, - does it need to be bled? |
Kansas 914 |
Aug 26 2014, 08:52 AM
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#1
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Advanced Member Group: Members Posts: 2,999 Joined: 1-March 03 From: Durango, Colorado Member No.: 373 Region Association: Rocky Mountains |
I have a VDO oil pressure gauge in the center console gauge cluster. It is a mechanical gauge - oil line from the sending unit location on the top of the engine to the back of the gauge. I noticed this weekend the line near the gauge is full of air and only a little bit of oil in the line. Should I "bleed" the line somehow. If so how is that done?
Can I just open the line at the gauge and keep it higher than the sending unit area so the air will rise? Thanks in advance! |
76-914 |
Aug 26 2014, 09:06 AM
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#2
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,485 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
Air is OK. Doesn't change the indicated pressure reading.
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00r101 |
Aug 26 2014, 09:21 AM
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#3
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Newbie Group: Members Posts: 17 Joined: 24-May 12 From: United States Member No.: 14,476 Region Association: MidAtlantic Region |
Air is OK. Doesn't change the indicated pressure reading. Ahhh, My high school physics says that a gas is compressible but a liquid is not as much. So air in the line will be compressed a bit as oil pressure changes. But whether it will make a huge diff in the oil pressure reading I do not know. Air in the line will start off at 14.7 psi so how much it will compress at say 60 psi i might be minimal |
76-914 |
Aug 26 2014, 02:09 PM
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#4
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,485 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
What weighs more? A pound of feathers or a pound of lead.
Which is the greater? 40psi of oil pressure or 40psi of air pressure. I don't think the gage can tell from whence comes the pressure. Only the amount present. |
SLITS |
Aug 26 2014, 02:12 PM
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#5
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"This Utah shit is HARSH!" Group: Benefactors Posts: 13,602 Joined: 22-February 04 From: SoCal Mountains ... Member No.: 1,696 Region Association: None |
Air is OK. Doesn't change the indicated pressure reading. Ahhh, My high school physics says that a gas is compressible but a liquid is not as much. So air in the line will be compressed a bit as oil pressure changes. But whether it will make a huge diff in the oil pressure reading I do not know. Air in the line will start off at 14.7 psi so how much it will compress at say 60 psi i might be minimal Oh yeah! And when you hook up the gauge and the line is filled with air, it will still read ZERO. If sea level air pressure were a consideration, the gauge would read 14.7 psig in the package. |
stugray |
Aug 26 2014, 06:53 PM
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#6
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
I even use a accusump pressure gauge as my mech oil pressure gauge.
That gauge is supposed to read the air pressure on the dry side of the piston in the accusump, but it seems to work just fine reading the oil directly. I was even hoping that an air bubble would remain in the grease hose that connects it to the block. The air bubble IS compressible so it would act as a water-hammer (in this case oil-hammer) buffer and the gauge wont see as high of pressure spikes. |
mikesmith |
Aug 28 2014, 08:56 PM
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#7
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Member Group: Members Posts: 202 Joined: 5-September 13 From: SF Member No.: 16,354 Region Association: Northern California |
Air is OK. Doesn't change the indicated pressure reading. Ahhh, My high school physics says that a gas is compressible but a liquid is not as much. So air in the line will be compressed a bit as oil pressure changes. But whether it will make a huge diff in the oil pressure reading I do not know. Air in the line will start off at 14.7 psi so how much it will compress at say 60 psi i might be minimal The pressure from the oil side in the line will be X psi. This will compress the air until the pressure from the air side is also X psi. With air in the line, the gauge will move a little slower (since oil will have to flow up/down the line as the pressure changes), but once it's stable, the air pressure will match (precisely) the oil pressure. This is also high-school physics. Remember the water column experiment? |
mgp4591 |
Aug 29 2014, 12:13 AM
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#8
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914 Guru Group: Members Posts: 5,363 Joined: 1-August 12 From: Salt Lake City Ut Member No.: 14,748 Region Association: Intermountain Region |
Air is OK. Doesn't change the indicated pressure reading. Ahhh, My high school physics says that a gas is compressible but a liquid is not as much. So air in the line will be compressed a bit as oil pressure changes. But whether it will make a huge diff in the oil pressure reading I do not know. Air in the line will start off at 14.7 psi so how much it will compress at say 60 psi i might be minimal The pressure from the oil side in the line will be X psi. This will compress the air until the pressure from the air side is also X psi. With air in the line, the gauge will move a little slower (since oil will have to flow up/down the line as the pressure changes), but once it's stable, the air pressure will match (precisely) the oil pressure. This is also high-school physics. Remember the water column experiment? |
hblyle |
Aug 29 2014, 12:31 AM
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#9
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Member Group: Members Posts: 64 Joined: 23-May 11 From: Huntington Beach Member No.: 13,110 Region Association: Southern California |
All physics aside, I would replace that plastic line with the copper upgrade. It won't get brittle in the heat and you won't see the air bubbles.
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barefoot |
Aug 29 2014, 06:45 AM
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#10
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Senior Member Group: Members Posts: 1,268 Joined: 19-March 13 From: Charleston SC Member No.: 15,673 Region Association: South East States |
Air is OK. Doesn't change the indicated pressure reading. Ahhh, My high school physics says that a gas is compressible but a liquid is not as much. So air in the line will be compressed a bit as oil pressure changes. But whether it will make a huge diff in the oil pressure reading I do not know. Air in the line will start off at 14.7 psi so how much it will compress at say 60 psi i might be minimal The pressure from the oil side in the line will be X psi. This will compress the air until the pressure from the air side is also X psi. With air in the line, the gauge will move a little slower (since oil will have to flow up/down the line as the pressure changes), but once it's stable, the air pressure will match (precisely) the oil pressure. The only thing a little air in the line will do is slow down the response rate of pressure change. the air will act as a capacitance just like an accumulator will in a hydraulic circuit. Barefoot |
Mike Bellis |
Aug 29 2014, 08:48 AM
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#11
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None |
Aside from all the physics BS, I bleed mine so the gauge will read pressure faster.
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stugray |
Aug 29 2014, 10:52 AM
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#12
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
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