Mechanical oil pressure

[Kevinstone]

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.

[ndutton]

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.

[Marty Levenson]

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.

[Al Schober]

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.

[Marty Levenson]

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?

[joe_db]

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.

You need something rated for at least 300 PSI. Copper is common, but you need a flexible section between that and the engine. As mentioned, grease gun hose is a cheap way to acquire such a thing. Gauges usually come with cheap nylon hose I do not trust at all.
5-6 feet should be no issue. I could see a really long line on a really cold day giving false low readings.

[Kevinstone]

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

[joe_db]

You may want to find a better gauge. The connection should be a flare or maybe compression.

[romantic comedy]

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.

[Marty Levenson]

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.

[joe_db]

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.

Even if the hose blows up like a balloon the pressure should be the same at the other end. This does not make a lot of sense

[Kevinstone]

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?

[joe_db]

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?

I would *not* use fuel line. It normally runs at about 5 PSI. No need to bleed the gauge, it doesn't really matter if oil or air gets shoved up to the gauge.
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

[sastanley]

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.

[Marty Levenson]

Hmmmm..

Even if the hose blows up like a balloon the pressure should be the same at the other end. This does not make a lot of sense

I'm ignorant but curious about this. If the balloon continues to expand, isn't some of the system pressure going toward strtching the balloon rather than pushing on the meter's sensor?

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?