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#1
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Oil line for gauge
Hi all
I’m wondering what is the proper size of tube for the oil line that goes to the gauge? Also does anyone have pictures of this lines route? I’m interested in what was used on a Cab13 Chevy.
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Jordan Baker RHLI Museum, Otter LRC C15A-Wire3, 1944 Willys MB, 1942 10cwt Canadian trailer |
#2
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Next question...do you bleed the line or does the oil find its way to the gauge despite the air in the line?
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#3
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Quote:
Regarding "proper" size, most (all?) civilian pattern Chevrolet gauges I've seen used a small/capillary line. I'm sure I've seen the round gauges with larger (3/16" or 1/4") OD line (the fitting on the back of your gauge may help on sizing) but I'm not sure if I remember capillary line being used as well. Parts book C15A-04 section 1.519 lists 1/8" tubing (tubing is normally specified by OD as opposed to pipe which is by nominal ID) for use as "Oil Pressure Gauge Pipe" which is a bit larger than the capillary tube I'm thinking of. |
#4
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If air in the line the oil would compress it possibly giving a false reading. It seems to me any time I've taken the line off the back of a gauge there's oil in it right up to the gauge. Probably over time the line bleeds itself.
Early square Chev gauges were capillary but the think the fitting on the back of a round gauge is 1/4" Quote:
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#5
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How would air in the line give a false reading? If you put 20 pounds of oil pressure onto the pocket of air, it would compress to 20 pounds.
Re the line, while I can't speak as to the correct size for the Chev (but have usually used 1/8 tube with compression fittings), I would advise that you usually add a pigtail to the line at the engine to absorb the difference in movement from the engine to the cab. Otherwise, the line can, over time, become brittle at the point where it absorbs most of the flex, and break. The actual thread for a 1/8 compression fitting is 5/18 x 24, the same as used on a 5/16 UNF nut or bolt. If that is the thread on your gauge, then that will be the tube size used. Last edited by rob love; 13-07-19 at 17:17. |
#6
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In particular, the Daimler Scout Car has a long oil pressure pipe, possibly about 10 feet and you have to bleed them off at the gauge in order to get a reading, once done it is OK then. Have had to do this a number times, and only recently on a fire engine with a Rolls engine in it.
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Richard 1943 Bedford QLD lorry - 1941 BSA WM20 m/cycle - 1943 Daimler Scout Car Mk2 Member of MVT, IMPS, MVG of NSW, KVE and AMVCS KVE President & KVE News Editor |
#7
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If I recall from my high school physics a gas will compress more than a liquid. Otherwise I'd use air in my hydraulics.
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#8
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Absolutely, but since the supply of oil will be more than required for the line and to do the little amount of work required within the gauge, it will compress the trapped air to an equal pressure, which will be read by the gauge. . There may be a slight to negligible delay in the reading of the gauge as the air compresses or decompresses, but it will be too slight to notice.
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#9
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Here is a link to the same discussion over on the HAMB: https://www.jalopyjournal.com/forum/...e-gauge.31196/
One fellow mentions something that I was thinking about re air in the line: It can act as a shock absorber if there is pulsing of the supply. Now that is not really a big problem on the engine oil pressure system, but I do run into it on well pumps and in some hydraulic and fuel systems. There are dampers/accumulators that can be installed to counter this. |
#10
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Quote:
I have to disagree on your last sentence, referring to one particular vehicle, (Daimler Dingo). If you have been working on it and go to start up and nothing showing on the gauge, alarm bells ring. I can tell you that it is much more of a delay than you describe, possibly due to the length of pipe. There is a difference between theory and practice. Having had 52 years on engines you don't take chances!
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Richard 1943 Bedford QLD lorry - 1941 BSA WM20 m/cycle - 1943 Daimler Scout Car Mk2 Member of MVT, IMPS, MVG of NSW, KVE and AMVCS KVE President & KVE News Editor |
#11
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Richard
In the case of the Dingo, or any other similar transmission of a signal over a long length of tube, I'll agree. But in the case of the usual 2 foot length of tubing as used on normal vehicles, It is not a great consideration. I had an interesting experience with the plastic tubing for an oil gauge which I would like to relate. It was on a M38 Jeep that had been converted to 12 volt. I was driving it when suddenly I had a bunch of smoke and the oil gauge reading zero. I immediately shut off the vehicle and opened the hood. The oil line had somehow contacted with the exhaust manifold and melted open. It then melted shut. I was able to continue on my way. I'll never use the plastic stuff again. |
#12
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Quote:
Most of the armoured vehicles of days gone by, had engines in the rear with several Yards of pipe ( Metres to you guys ). Nowadays it is all done by electrickery sensors.
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Richard 1943 Bedford QLD lorry - 1941 BSA WM20 m/cycle - 1943 Daimler Scout Car Mk2 Member of MVT, IMPS, MVG of NSW, KVE and AMVCS KVE President & KVE News Editor |
#13
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I'm with you Rob. Many gauges come with a very fine capilliary tube. Some are long. There is no way to bleed the air out of them. The gauge is usually mounted higher than the other end and is not designed to be bled of air. Thick cold oil in the tube would have friction and be slow to move. However air would be instantaneous.
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... |
#14
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Quote:
We are not talking sealed capilliary gauges, the ones I were referring to have a pipe nut connection at the gauge, you slacken the nut off and run the engine until oil appears, nip up the nut and it is all sorted.
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Richard 1943 Bedford QLD lorry - 1941 BSA WM20 m/cycle - 1943 Daimler Scout Car Mk2 Member of MVT, IMPS, MVG of NSW, KVE and AMVCS KVE President & KVE News Editor |
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