#1
IP: 107.72.164.133
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Mechanical oil pressure
Hi guys, does anyone know what the correct type of tubing for a mechanical oil pressure gauge should be? Can I use rubber fuel line? What's the maximum length for the tubing? I think 5-6 feet would get the gauge where I want it.
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#2
IP: 24.152.132.140
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It depends on the rating of the fuel hose. When I relocated my oil pressure senders/switches off the engine to a bulkhead I used hydraulic hose, 300 psi rated available at NAPA. Be sure to use a proper hose barb fitting in the block.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#3
IP: 108.172.151.75
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copper
I tried hydraulic (grease gun?) hose (can't recall psi rating) that our NAPA store swore would work. Tested fine initially but on a long motor got false low reading as the oil temp rose. Went back to copper.
We run at 180 degrees.
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Marty 1967 Tartan 27 Bowen Island, BC |
#4
IP: 32.211.28.40
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When I moved my OP sender off the block, I used a tube from Home Depot meant for a grease gun - about 12" or 18" long. End fittings were 1/8 NPT so no issues. Not expensive.
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#5
IP: 108.172.151.75
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hose length
Al: I'm wondering if hose length accounts for your grease gun hose working and mine not working. I'm guessing that for me the run from the block to the meter was about 3.5 feet. Kevinstone estimated he needs 5-6 feet.
Also, how hot do you run?
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Marty 1967 Tartan 27 Bowen Island, BC |
#6
IP: 137.103.82.194
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Quote:
5-6 feet should be no issue. I could see a really long line on a really cold day giving false low readings. |
#7
IP: 107.72.164.133
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Thanks guys, I'll
Check out what auto parts have to offer. My gauge has a nipple which would require a flexible hose and hose clamp. Engine block end will Take an npt barb |
#8
IP: 137.103.82.194
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You may want to find a better gauge. The connection should be a flare or maybe compression.
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#9
IP: 71.208.55.235
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I hooked up an oil pressure gauge on my old VW bus. I ran that plastic extension tubing from the engine (in the back) all the way to the dashboard. It was at least a 10 foot run. I bled the tubing and had oil all the way to the gauge. It was so accurate I would see the oil pressure drop as I shifted.
That was for a 67 bus a long time ago. |
#10
IP: 108.172.151.75
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heat and length
Trying to understand why other hoses have worked.
Found the hose that I initially used for the oil pressure gauge: 4 feet long, 300psi grease gun hose. There is no doubt it caused the gauge to receive misleading pressure. Running at temp for a couple hours on a hot day the reading fell steadily from 20 to 8. (Same gauge directly on the block worked perfectly, and when reinstalled with a copper tube works fine.) I do believe that running at 180 with a long run caused the hose to get too soft to maintain the pressure the rest of the system has. perhaps others are running at a lower temp or have a shorter run? Or my hose was defective (unlikely)? There is no flexible connection at either end.
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Marty 1967 Tartan 27 Bowen Island, BC |
#11
IP: 137.200.0.106
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Quote:
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#12
IP: 107.72.164.133
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Thanks for all the tips. I am leaning towards copper from engine with a short piece of fuel line at the gauge. Still
Need to see what I can find. Currently drifting around the keys, will check next time we land at a town. Is it necessary to bleed the tubing up to the gauge? |
#13
IP: 137.200.32.22
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Quote:
You need to find a good hardware store, hydraulic shop, or perhaps NAPA. Grease gun hoses work and our local hardware store makes up all kinds of high pressure hydraulic lines with various fittings. You need something that can deal with hot petroleum products at 100 PSI. This is also likely why electrical oil pressure gauges are common Last edited by joe_db; 01-22-2019 at 02:43 PM. |
#14
IP: 206.125.176.3
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KS, An auto parts store should have a copper tube kit for exactly this purpose. I think I got one at an Advance Auto store. The copper should be more accurate and less prone to failure than plastic that typically comes with the gauge, although I have used both..when I was a kid and broke, it was a plastic tube thru the firewall to my gauge set on the '78 Civic. On my current project car, a '91 Civic, I 'upgraded' to copper when I installed an OP gauge.
And yes, you'll want to bleed it so you don't have air in the line, which could affect accuracy.
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-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) |
#15
IP: 108.172.151.75
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Hmmmm..
Quote:
I'm curious because I can't see another explanation for my experience with the 4' hose, as stated in a previous post. Question please: is anyone running at 180 with a longish non copper connection?
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Marty 1967 Tartan 27 Bowen Island, BC |
#16
IP: 137.103.82.194
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Quote:
I have hooked up a number of oil pressure gauges and none of them ever needed bleeding. Pressure gauges on airplanes can have a lot of hose between the cockpit and an engine on the wing and they don't have bleeds. If there is 100 PSI oil at one end of a sealed pipe, it will move up the pipe until it meets 100 PSI air |
#17
IP: 108.172.151.75
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pressure
...but isn't the hose ("balloon") steadily inflating as it gets hotter and hotter?
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Marty 1967 Tartan 27 Bowen Island, BC |
#18
IP: 64.62.192.42
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I think the gauge I got at NAPA came with 1/8-inch polypropylene tubing. (Not positive - could be PE or nylon, but I think PP is better with heat, oil, and pressure.) It came with quite a lot. At least ten feet. Maybe they have more at NAPA? Hardware stores tend not to stock the smaller sizes. I wouldn't use flex stuff like fuel line.
I use 1/8-inch PE up to 100 PSI for lab gases every day, at room temperature. Hot oil might be another story. I've got 1/16 PP tubing running at 2000 PSI liquid, but it does fail from time to time. Then there's PEEK, but that, and fittings for it, are expensive. Anyway, my usual source for all that is Cole Parmer, except PE tubing can usually be had at Ace Hardware. May be cheaper to just buy a new NAPA gauge with tubing and fittings included. Or heck, the whole mess is just sitting in my parts box. Could make you a great deal... |
#19
IP: 72.194.222.152
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Quote:
It lasted ~ two years before it rusted out. A "marine rated" gauge would have lasted longer. TRUE GRIT |
#20
IP: 137.103.82.194
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It is open at each end. It would have to inflate pretty quick to make a noticeable change and it would then be popping and shooting oil all over. Slowly changing from 0.25 to 0.29 inches would do nothing on the gauge. I am talking something like 0.25 to 6 inches swelling rapidly The hose would pop before the gauge settles down.
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