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post #1 of (permalink) Old 09-01-2005, 10:03 AM Thread Starter
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Mechanical oil pressure gauge

Installing a gauge on the JeePullr (F250). Has a hose that runs from the block to the back of the gauge. Instructions don't say anything about purging the air from this line. Should I? It would seem that I would want the oil to come to the gauge and not count on the compression of the air in the line to give me a reading on my oil.
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post #2 of (permalink) Old 09-01-2005, 12:22 PM
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Re: Mechanical oil pressure gauge

I installed mine just like that. Not sure if I should have hand cranked it to fill the line or not...
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post #3 of (permalink) Old 09-01-2005, 12:25 PM
 
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Re: Mechanical oil pressure gauge

That's fine. Pressure is pressure... doesn't matter if the air compresses.
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post #4 of (permalink) Old 09-01-2005, 12:31 PM
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Re: Mechanical oil pressure gauge

As was said, just screw it on the back of the gauge and start her up. You will always have air in there. Say you purge all the air and start her up. Everything is fine and dandy and you have a big satisfied grin on. Now shut her down overnight and come to find out that the oil that was nice and airless in the line has since drained back down. Start it up again and you now have air..... Sorry for the sarcasm, just one of those days.
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post #5 of (permalink) Old 09-01-2005, 07:38 PM
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Re: Mechanical oil pressure gauge

Yeah, you're not needing the volume to move something like brakes, you are measuring the pressure. As was said, pressure is pressure whether the oil or air is transmitting it.
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post #6 of (permalink) Old 09-01-2005, 07:50 PM Thread Starter
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Re: Mechanical oil pressure gauge

Thanks guys. I got impatient and went out, cranked it over a few times, bled all the air, hooked it up. Fired the motor up and found out how much the stock oil pressure gauge has been lying to me...

Oh, and it has air back in it now...No need to bleed...
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post #7 of (permalink) Old 09-02-2005, 09:27 AM
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Re: Mechanical oil pressure gauge

I've installed many mechanical oil pressure gauges. I never "purged" the line. Be sure your lines are protected from the areas of excessive abrasion. I've only had one oil pressure line leak in 30 years, but what a mess!!
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post #8 of (permalink) Old 09-02-2005, 10:22 AM
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Re: Mechanical oil pressure gauge

One other problem with mechanical gauges is that the capillary tube (the tube that carries the oil) can fracture with vibration. Take GREAT CARE in routing that tube so that it has as much support as possible and if you've got the length, install a vibration loop (similar to the vibration loops on a Brake MC assembly).

There's nothing less fun than fueling up and seeing a oil trail behind your Jeep and thinking: "That poor guy's going to have a problem...", only to find that the oil trail came from YOUR Jeep.

Don't ask me how I know.
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post #9 of (permalink) Old 09-02-2005, 10:33 AM
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Re: Mechanical oil pressure gauge

Having air in the line can have advantages and disavantages...
With air in the line, it has a natural dampning effect....hence, your needle will not bounce as much or show the pulses in the oil.
Without air, the oposite is true....the needle will show 'all' pulses. (one of the reasons they make oil filled gauges)

But as you have found, pressure is pressure. But make sure you heed Leve's advice ....protect that line. I have seen a few guys that ended up with a floor board full of oil.
post #10 of (permalink) Old 09-02-2005, 11:19 AM
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Re: Mechanical oil pressure gauge

Probably does not need to be said, but - just in case - TOSS that POS nylon tubing that came w/ the gauge, and get yourself copper tubing of same size (1/8"). The nylon tubing WILL leak - not a question of 'IF', but 'WHEN'. (Refer back to Larry's post...)
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