Dumb question - Bleeding an oil presure gauge?

It'll work it's way out. Don't worry about it.

 

Mercedes factory-installed oil pressure guages work the same, with the little tube and all. No need to bleed. The hydraulic pressure just compresses the air, guage reads the pressure, air and oil together.
Cosmo

 

Dammit, Grimlock, this is a TRADITIONAL board and the moderator should toss you out when you start talking about mulletmobile tech!
Oil pressure gauge lines are COPPER with a just-so spiral to absorb engine movement. Now, you can't SEE the bubbles, so they AIN'T THERE.
Got that?

 

The air won't compress at the same rate as the oil. You should bleed the line by placing the open end inside a container, such as two-liter pop bottle. Tape the tube to the bottle so it doesn't go flying when you start the car. Bump the ignition and shut it down right away. I shouldn't take long to get a full stream of oil.

Does a little air really affect the operation of the gauge? Not really. They're not that accurate anyway, its just good workmanship.

 

I've never bled a gage oil line...there's usually something more important to do instead.

But I did get rid of that funky late model billet oil gage on my 55 a couple weeks ago, the line at the engine cracked or something and started dripping on the header, so I pulled it out and plugged it. Still have the factory idiot light in the dash with a 20 psi sender, so I'll be fine.

 

The air bubble may change size when it is subjected to a certain pressure but that won't change the pressure that surrounds it.

 

you could have air, water, antifreeze, or any fluid in line and the pressure would still be uniform though out the line

 

Years ago I tried to blead an oil pressure guage line. Tried for an hour to get rid of the air, no luck! Everytine I started the motor, more air appeared. My boss at the time watched and smiled, after an hour or so he informed me that since the oil system is not a closed system, it was going to be awfully hard getting the air out of the line. Every time you shut if off, the oil drains back into the oil pan, pulling air into the system from any place that has any clearance. When you restart the motor, the oil pump replaces the air with a new load of oil.

The hard lesons are the ones you remember! Gene

 

It doesn't matter. The air bubbles will not throw off the reading, don't worry about the line being filled with oil.

 

Like I tell my students... "There's no such thing as a dumb question... there's only dumb people who ask questions"

No, you don't have to bleed it.

Sam.

 

I think we should vote on if its a dumb question or not!! '
I think it is!!lol
JimV

 

When I went to a larger steel braided line in my race car I had oil pr.problems when I backed of at the end of a race. I bleed the oil line problem solved but this was a bigger line. As for that plastic oil or break line if you ever seen what it does in a fire you would not us it. I had a front row seat in this one no more plastic for me

 

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The air won't compress at the same rate as the oil. You should bleed the line by placing the open end inside a container, such as two-liter pop bottle. Tape the tube to the bottle so it doesn't go flying when you start the car. Bump the ignition and shut it down right away. I shouldn't take long to get a full stream of oil.

Does a little air really affect the operation of the gauge? Not really. They're not that accurate anyway, its just good workmanship.

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SO would you bleed the line everytime you start the car?

I didn't think so. It isn't nessasary to bleed the line,ever. It's magic

 

Air cant get into the gage so it holds the oil in the line even when its shut off it wont drain out unless you have a leak. Its like putting a straw in a glass of water and putting your finger over it. the water will stay in the straw till you take your finger of

 

because with the brake system your dealing with thousands of pounds of pressure, rather than the 30-50 of the oil system... and if your oil gauge isn't totally accurate, big deal.
If your brake system isn't totally accurate however....

 

Plus, you gotta get that cruddy black brake fluid out now and again, so your hydraulics don't gum up

spongy brake pedal can be bad I guess, but nothing extra leg muscle won't solve.

but the above post nailed it.. there's less margin of error at 30-50 psi on your gauge versus the brakes, which are high pressure, and you can actually feel the difference..

 

I stand by my recommendation. You probably would never notice any difference in the operation of the gauge or ever care. It is a fact however that the air in the line will slow the reaction time of the gauge.

The needle of the gauge moves because of the variation in the oil pressure within the feed line. Any hydraulic device works because the liquid oil is considered non-compressible. When an increased pressure is applied, the liquid will move to an area of lower pressure through the path of least resistance, until the pressure is equalized. The volume will remain the same. If the liquid has no place to move, the liquid pressure will rise proportionally to the applied pressure.

The theory known as Boyle's Law states: If the temperature remains constant, the volume of a given mass of gas is inversely proportional to the absolute pressure. The gas will compress while the oil won’t. It’s like air in you’re your brake lines. The air will compress a bit and make the brakes feel “spongy”.

I have successfully used my technique to bleed an oil gauge line. It works for me. I haven’t seen air return when I used a clear plastic line. That’s just the way I do it. Install yours however the hell you please. It really doesn’t matter either way.

 

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why is is so crucial to get them out of the brake lines?

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Because you have a limited amount of pedal stroke and can only bring so much fluid in at one time.
One reason why pumping the brakes helps a low pedal.

An engine oil system has - in a manner of speaking - an unlimited supply of pressurized oil to compress all the air bubbles in an oil pressure line.
The brake system doesn't.

 

There is a big differince on breaks and its not as much the pre. as the volume. A master cyl has only so much volume and breaks have alot longer lines so they get even more air. Since air compreses and oil and break fluid dont when you hit the breaks and the air compresses in the lines it uses up the masters cyl. volume. If you have enough air you wont have breaks at all. On a oil gage there is not that much line and the oil volume will not runout unless you have a problem. air in a oil line will make the gage respond slower and if you have a big enough cam and large enough lines your gage can read low and very eraidick as happened in my race car

 

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Well I'm not going to worry about bleeding the line...but if air bubbles really don't effect line pressure then why is is so crucial to get them out of the brake lines?

Good thing I have a circuit built in for installing electric gauges later.

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I never bleed my breaks..

 

Grimlock I dont think this was a dumb qustion. I do agree that most time bleeding an oil line is no big deal. Air in the line DOES make a diffrence but usualy not enough to worry about. In some casses like my race car it makes a big diffrence. I pulled one moter out and had another built at a cost of 6 grand cause I thought I had a oil problem. When I put the new one in I still had the same problem. When my moter builder told me to try to bleed the line my oil problem went away So what you are calling a dumb Qustion cost me 6 grand to learn the ansser to.

 

If I've learned anything here it's that some of you dingle-berries can't spell worth a damn

Of course the more air in the line the less accurate the gauge will be, it's common sense.

On a small line like you are talking about just bleed it once and forget about it.

Working in the engine rooms of the ships in AK we actually had petcocks at the gauges to bleed the lines periodically.

Those lines were much larger so the volume of air trapped in the lines would make a definite difference.

Conversely, a very small amount of air would actually reduce the amount of shock to the gauge, give a steadier reading and extend the life of the gauge.

Paul

 

A side issue: The real reaction time problem on oil pressure is the driver. The gauge is a good monitor of engine condition, oil deterioration, and such, but you can't drive watching the gauge all the time. I think a simple idiot light should be fitted along with the gauge to alert the driver to sudden failures.
Oil pump failure is rare in flatheads and SBC's (and common in certain other engines), but it can happen, and there is always the possibility of a gallery plug or filter line/gasket failing and causing engine damage very quickly.
I've heard several horror stories involving Checvy pickups with the externally plumbed cooler--that one is in the main flow, and so can completely dump the oil faster than you can say "huh?". A well placed idiot light gives you a much better chance of catching that kind of failure while you still have a usable crankshaft.

 

[ QUOTE ]
If I've learned anything here it's that some of you dingle-berries can't spell worth a damn

Of course the more air in the line the less accurate the gauge will be, it's common sense.

On a small line like you are talking about just bleed it once and forget about it.

Working in the engine rooms of the ships in AK we actually had petcocks at the gauges to bleed the lines periodically.

Those lines were much larger so the volume of air trapped in the lines would make a definite difference.

Conversely, a very small amount of air would actually reduce the amount of shock to the gauge, give a steadier reading and extend the life of the gauge.

Paul


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What he said..
A little air may stop guage needle flutter


and,
Breaks are for Coffee & Doughnuts, and dropped Mirrors.
Brakes stop a car.

 

"Brakes" use hydraulic fluid which has different properties than oil and serves a different purpose. Grimelock just crack the fitting a little and crank the motor till you see it dripping then tighten it back down that'll get most of the air out.

 

So I cant spell. That never hurt me in my race car or my shop working on my cars. The REAL Dingle-berries or those that are to DUMN to learn from others mastakes! Just because its never happenen to ya dont mean it wont.