Pressure gauge replacement

[hangarb7]

Greetings. Need to replace the pressure gauge. Questions, I do not see where these original type gauges are now available. I do see one in Wag Aero that has the 'capillary' which to me indicates a tiny oil tube like the old school car gauges. Is this what I want?

Second question, when attaching a new gauge and hose, do I need to prime the line at installation or will the oil find its way to the gauge by itself? (is it possible to get an air bubble that would give problems?)

Thanks
JackD
44057
'46 TC BC12D with the original 65 continental

[3Dreaming]

The capillary is typically for oil temp gauges.

You should be able to find a used serviceable oil pressure gauge, it is the oil temp gauges that are hard to come by.

[hangarb7]

oops, you are correct about the capillary. Reading so many that I was looking at the wrong gauge. So where would I find a used gauge? I actually have been asking around for a few weeks. Can't fly without it. And I still need to know if I need to prime the line..... see first post questions. Thanks

[3Dreaming]

Priming the line is not completely necessary, but you will get a quicker oil pressure indication with fluid in the line. If you are in a extremely cold climate I have heard of filling the line with hydraulic fluid from the engine back to the gauge, otherwise with the engine running crack the "B" nut on the back of the gauge, Just be ready with a rag to clean up the mess.

As far as used gauges go they pop up on here from time to time, also on the Facebook page.

[Robert Lees]

You probably won't need to prime the line. Any air in the line will be pressurised to the same as that of the oil. But if you wish, you can loosen the union at the back of the gauge (engine needs to be running, of course).

There is a gauge on eBay UK, but I fear the threads will be different:

https://www.ebay.co.uk/i/154415994118?ul_noapp=true

[PA1195]

Filling my oil pressure line with Mil-H-5606 brake fluid helped improve the gauge response in cold weather. Mech pumped it in at the engine end until it bled out the loosened fitting on the gauge. That was after we flushed the line with spray brake cleaner solvent to remove 70+ years of black oil residue and crud.

Gary

[Robert Lees]

Filling my oil pressure line with Mil-H-5606 brake fluid helped improve the gauge response in cold weather. Mech pumped it in at the engine end until it bled out the loosened fitting on the gauge. That was after we flushed the line with spray brake cleaner solvent to remove 70+ years of black oil residue and crud.

Gary

For the small additional cost, I would suggest replacing the tubing for fresh.

For the information of all: make sure the engine-end of the oil pressure line has a restriction in case the line fails in the future. As an example, I use this modified AN840-4D fitting with a #40 hole:

[PA1195]

Yes Robert a replacement line would have been nice.....but local Techs get $120/hour to move and fix things. A line has to be fabricated....material and fittings.....then installed safely and tested for leaks. Log entry made ref: New oil pressure line fabricated and installed this date. Checked for leaks, etc. It was that or a $5 can of brake cleaner and some 5606 from my brake fluid squirt can. We did clean and anneal the existing copper line (heated after flushing with a torch then dropped it onto snow to quench) then reinstalled it.

Gary

[Robert Lees]

Yes Robert a replacement line would have been nice.....but local Techs get $120/hour to move and fix things. A line has to be fabricated....material and fittings.....then installed safely and tested for leaks. Log entry made ref: New oil pressure line fabricated and installed this date. Checked for leaks, etc. It was that or a $5 can of brake cleaner and some 5606 from my brake fluid squirt can. We did clean and anneal the existing copper line (heated after flushing with a torch then dropped it onto snow to quench) then reinstalled it.

Gary

Good for you! What the eye can't see, the heart can't grieve over

[hangarb7]

Yes Robert a replacement line would have been nice.....but local Techs get $120/hour to move and fix things. A line has to be fabricated....material and fittings.....then installed safely and tested for leaks. Log entry made ref: New oil pressure line fabricated and installed this date. Checked for leaks, etc. It was that or a $5 can of brake cleaner and some 5606 from my brake fluid squirt can. We did clean and anneal the existing copper line (heated after flushing with a torch then dropped it onto snow to quench) then reinstalled it.

Gary

Gee Gary, how long ago did you do that? I was taught to anneal the tubing by slowly letting it cool, not hardening it by rapid cooling. Now I would like to hear from others.....

[PA1195]

I may still replace that copper line with new or something flexible. I've had them crack before despite a flex loop in the engine compartment. Not worth saving $$$ over but it was winter and oil pressure took some time to register despite having a warm engine pre-start. Gunk in line probably a factor.

Gary

[PA1195]

Gee Gary, how long ago did you do that? I was taught to anneal the tubing by slowly letting it cool, not hardening it by rapid cooling. Now I would like to hear from others.....

That was three years ago. I suppose it can be done both ways...slow cool or quench in water or snow in this case. Look up copper annealing....opposite of hardening steel. Same for spark plug copper gaskets....heat until cherry red then drop in cold beer. Don't waste the beer.

Gary

[Hank Jarrett]

Copper is NOT the same as steel or aluminum! Copper tube is annealed by heating it and then cooling it RAPIDLY. If you allow it to cool slowly it will HARDEN. It will also harden when you bend and work it (why it is called "work hardening").

I understand the seemingly horrific cost of replacing the tube by an A&P IA but it is money well spent over having a oil pressure line break. You CAN do it yourself and just pay to have the A&P IA check your work, then sign it off. It is great experience and you will learn a lot about what is behind your panel.

When I replaced mine I added a bulkhead fitting at the firewall (with my IA's approval) and put a line from the engine to the fitting and another line from the fitting to the instrument. If you ever need to pull the engine or exhaust for any reason it will save you a BUNCH of time! DO NOT FORGET to put a restriction hole on the engine fitting. It significantly slows the loss of oil if the line is damaged and there was a requirement to add it decades ago that doesn't show up on the FAA list at annual. Another thing I did (with my IA's approval) was to use a much larger diameter line from the firewall to the instrument, stepped up at the firewall fitting. Once the air was bled from the line I got significantly faster oil pressure readings in the cockpit.

You DO NOT have to run the engine to prime the line. Mine primed just fine by pulling a plug from each cylinder and pulling the prop through (WITH THE MAGS OFF!) till I got oil from the loosened instrument fitting. A face full of cool oil is MUCH nicer than hot oil! I only lost a few drops.

Talk to your mechanic and see how much you can do yourself with his checking your work. It is actually a lot of fun and saves you a lot of time and him a lot of work that doesn't require an actual A&P IA to do.

Hank

[astjp2]

You probably won't need to prime the line. Any air in the line will be pressurised to the same as that of the oil. But if you wish, you can loosen the union at the back of the gauge (engine needs to be running, of course).

There is a gauge on eBay UK, but I fear the threads will be different:

https://www.ebay.co.uk/i/154415994118?ul_noapp=true

I have seen gauges bounce with air in them, no idea why, just do.

Van's aircraft carries the correct orifice that you screw into the case and its like an AN3 or 4 at a 45 degree angle. Much better price than Lycoming or Continental. Tim

[Edwin Otha]

You can go to the Stewart Warner home page for gauges,they have replacements. I use as wide a sweep I can find at the proper pressure range.

EO