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Old 05-07-2016, 07:38 AM   #1
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Live and learn (Oil pressure gauge lines)

Well, being a pile driving dummy and not a boat builder got me again!
I was having some tach cables made for the Rose and chatting up the tech about oil pressure for my DD's. The whole place had a good laugh about my 1/8" air lines I installed for oil pressure gauges on my engine and drives.
Next week I will have 4 new 1/4" hydraulic lines......That was what the boat had before I just didn't recognize them.
I'll post some video of the before and after to see if it really makes a difference on the readings and the quickness of operation. (They say it will)
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Old 05-07-2016, 07:58 AM   #2
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It will be interesting to see if it makes any difference.

I'm not sure why it would. Mechanical oil pressure gauges do not normally have nor need lines anywhere near 1/4" ID. to operate correctly. Which is huge for gauge feed lines.
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Old 05-07-2016, 08:04 AM   #3
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Greetings,
Mr. s. I tend to agree with Mr. 11. The larger the line, the more air it contains and that would lead to a slower response time overall as the air is forced to compress. I would have thought that 1/8" would be more than adequate.
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Old 05-07-2016, 08:10 AM   #4
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Well I bleed the air out of the lines when I install them, I am running 38' with the lines. Does that make a difference. It take about 5 seconds to read pressure at the helm when I start the engine.
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Old 05-07-2016, 08:16 AM   #5
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Greetings,
Mr. s. "Well I bleed the air out of the lines when I install them,..." OK, ya got me there. I was always under the impression that the oil pressure gauge lines contained air.
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Old 05-07-2016, 08:33 AM   #6
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Well I bleed the air out of the lines when I install them, I am running 38' with the lines. Does that make a difference. It take about 5 seconds to read pressure at the helm when I start the engine.
So you are doing all this to gain a couple seconds?
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Old 05-07-2016, 08:40 AM   #7
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No, the first issue I had was the newly rebuilt engine was reading less pressure at idle then the older engine. When I would run up the speed a little I would get different readings, I changed the gauge and it made a little difference but the pressure reading wasn't the same as the pressure from a short line from the engine. The second is the possibility of a 1/8" line wearing over time and dumping oil, not much but something to fix later.
My hope is with the new lines (1/4") to get more accurate readings on a more consistent basis.
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Old 05-07-2016, 09:16 AM   #8
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Quote:
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No, the first issue I had was the newly rebuilt engine was reading less pressure at idle then the older engine. When I would run up the speed a little I would get different readings, I changed the gauge and it made a little difference but the pressure reading wasn't the same as the pressure from a short line from the engine. The second is the possibility of a 1/8" line wearing over time and dumping oil, not much but something to fix later.
My hope is with the new lines (1/4") to get more accurate readings on a more consistent basis.
Makes sense, due to the smaller lines, takes longer to see the pressure change at the 38 foot farthest end. Yes, you don't want an air line to fail, would create an awful mess of oil hence the idea of hydraulic hose which is a tougher hose.
If the air hose is PVC, there is also a temperature problem, oil too hot will weaken the hose.
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Old 05-08-2016, 08:02 AM   #9
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Don't expect to see much oil pressure if you set the idle down much below 400RPM.

This is normal.
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Old 05-08-2016, 09:09 AM   #10
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Yea, I found out the hard way. I took the sending line (1/8") tubing off to see if any oil was flowing and a 1/4" stream of oil shot up about 4'. There's lots of volume and pressure.
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Old 05-11-2016, 07:56 PM   #11
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Ok, I got two lines made up and installed them today. The length was 40' and I have a side by side comparison of a cold start. I will leave it like this until I take my next run to see what it does when it's hot.
http://youtu.be/Lbbiqj7-mtA
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Old 05-11-2016, 11:58 PM   #12
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Thin sensing line vs large only affects how fast it responds to changes. Steady state ops they will both read the same.
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Old 05-12-2016, 08:06 AM   #13
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Thin sensing line vs large only affects how fast it responds to changes. Steady state ops they will both read the same.
Yes. The pressure should be the pressure no matter the line diameter, with in reason, I would think.
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