Electrical vs mechanical gauges

Big Ed

N50247 - '79 Super D
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During my ongoing annual, we discovered my oil temp sender bulb had broken off from the capillary tube. It probably happened during the annual, since it worked just fine on the flight before the annual. I probably weakened it with rough handling when I removed the oil pressure screen for cleaning at the last oil change. I had no idea what a capillary tube was, or how fragile it was, especially a 43 year old tube that has probably been removed several dozen times for pressure screen cleaning.

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Upon doing research for replacement, I was advised to replace it with an electrical gauge, which has a sender and wires instead of a bulb and capillary tube. I called ACA to get a gauge with screen printed arcs on the face, and ordered the Mitchell gauge from them. Cost is approx $230, which is reasonable as airplane parts go.

mitchell gauge.pngsender.jpg

That got me thinking about the oil pressure and fuel pressure gauges. They are similarly ancient tech. The oil pressure gauge relies on a flexible tube carrying hot oil to the gauge, while the fuel pressure gauge relies on a tiny steel line carrying pressurized fuel to the gauge. Neither is an appealing thought in the cockpit.

So that begs the question: should I go ahead and replace those two gauges with electrical units also?

Thoughts?
 

Bob Turner

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That fuel line really bothered me. I ordered the electrical gauge, and when it arrived the instructions were to mount the sender remotely and use a tube from the pump. Sort of defeats the purpose, since when they break it is at the engine, not under the instrument panel.

There ought to be a better solution - but they do not seem to break all that often. I am aware of just one.
 

Big Ed

N50247 - '79 Super D
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That fuel line really bothered me. I ordered the electrical gauge, and when it arrived the instructions were to mount the sender remotely and use a tube from the pump. Sort of defeats the purpose, since when they break it is at the engine, not under the instrument panel.

There ought to be a better solution - but they do not seem to break all that often. I am aware of just one.
Got a link for the gauge you used? Where was the sender mounted?

Maybe I'll ask the ACA guys when I visit them in 2 weeks. Surely they have figured out a better way in 43 years.
 

aftCG

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$230 for an airplane part? Are you sure that isn't just the box? My plane had an electric oil temperature indication but the mechanical oil pressure gauge. It worked fine and never leaked a drop. I would worry way more about that fuel shut off valve where the primer line exits before the shut off part. So a failed primer line anywhere from that valve to the firewall WILL result in 100LL joining you in the cockpit, with no way to stop it.
 

Big Ed

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$230 for an airplane part? Are you sure that isn't just the box? My plane had an electric oil temperature indication but the mechanical oil pressure gauge. It worked fine and never leaked a drop. I would worry way more about that fuel shut off valve where the primer line exits before the shut off part. So a failed primer line anywhere from that valve to the firewall WILL result in 100LL joining you in the cockpit, with no way to stop it.
LOL, roger on the price. Was a pleasant surprise. :D

I'm less concerned about the oil pressure than the fuel pressure. The electric oil pressure gauge and sender are even cheaper than the oil temp, like $150, so it's more of a "what the heck, while I'm in there" kind of thing.

Decathlons do not have a primer, so I do not believe that is a concern for me. Had a funny and somewhat unnerving exchange with my IA while he was looking at my cylinders and trying to find the primer. I kept saying "dude, it's fuel injected." :unsure:

I'll tell you what I do worry about: that header tank with 2 gallons of AVGAS hanging over my balls, with 4 fittings and lines running to/from it. As I understand our fuel system, the fuel is gravity fed from the tank to the gascolator. Fuel is not pressurized until it gets forward of the firewall and hits the boost pump. Presumably a minor leak in the cockpit lines would be just a drip, not a spray. That is why I'm not so much a fan of the pressure gauge line running back into the cockpit. I assume that line is stainless and pretty thick walled, but still.
 
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Bob Turner

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It is stainless. Still . . .

Ed- I did not install the electric gauge. It was pointless, since my goal was to get rid of the stainless line. I’d sell it for half price.

And yeah - downstream of the pump, so a break would mean an uncontainable explosive fire. Do we really need a fuel pressure gauge? Maybe they have invented better flex lines since 1977.

Don’t forget - the injector lines are made the same way, and they are supported in two places and subject to a recurring AD.
 

aftCG

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LOL, roger on the price. Was a pleasant surprise. :D

I'm less concerned about the oil pressure than the fuel pressure. The electric oil pressure gauge and sender are even cheaper than the oil temp, like $150, so it's more of a "what the heck, while I'm in there" kind of thing.

Decathlons do not have a primer, so I do not believe that is a concern for me. Had a funny and somewhat unnerving exchange with my IA while he was looking at my cylinders and trying to find the primer. I kept saying "dude, it's fuel injected." :unsure:

I'll tell you what I do worry about: that header tank with 2 gallons of AVGAS hanging over my balls, with 4 fittings and lines running to/from it. As I understand our fuel system, the fuel is gravity fed from the tank to the gascolator. Fuel is not pressurized until it gets forward of the firewall and hits the boost pump. Presumably a minor leak in the cockpit lines would be just a drip, not a spray. That is why I'm not so much a fan of the pressure gauge line running back into the cockpit. I assume that line is stainless and pretty thick walled, but still.
I need to get my head back into fuel injection. The radial engine for my Kitfox is now at the importer's facility. I'm ditching the carb for a throttle body injection system.
My header tank is one gallon and located behind the right seat. It would need to be a very unusual attitude before a leak soaked anyone's wedding tackle.
 

Big Ed

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Ed- I did not install the electric gauge. It was pointless, since my goal was to get rid of the stainless line. I’d sell it for half price.
Do you have a link or a model name/number for the gauge?

Where was the sender supposed to mount?
 

Big Ed

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Found this picture of installation method for a Mitchell fuel pressure sender. Bob, is this similar to what you were looking at?

I think I would rather have the fire out there than in my lap.

Fuel-sensor-A.jpg
 

Big Ed

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@#-$+&_**&!!!

Got the new Mitchell gauge. It is 2 1/4". Tried it out and realized the old SW gauge and panel hole are 2" even. There is very little excess material between the gauges, and between the gauge and edge of the panel. Little room for error when cutting a larger hole.

Aggravating for 2 reasons. First, ACA had a replacement capillary tube and bulb for the old gauge for 90 bucks. Second, I am running out of time to get my aircraft out of annual and make my planned timeline to Oshkosh. Only 5 work days left.

So now I am left with 2 bad choices. A) Have the A&P hack away at the panel trying to fit the electrical gauge, or B) lose 2 more days having the analog sensor overnighted from Wisconsin.
 

aftCG

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Definitely B. Plan A will always uncover more issues that need to be solved, and if one of those requires ordering parts then you already lost those days.
 

Big Ed

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Definitely B. Plan A will always uncover more issues that need to be solved, and if one of those requires ordering parts then you already lost those days.
So far that has been the pattern. Looked at it closer today and I think it might be doable. I'm going to discuss with the A&P tomorrow morning. Deadline to get the part overnighted from ACA is noon eastern. I think it fits, and the corner can be shaved down. My biggest concern is my A&P not having an instrument hole cutter and resorting to a sloppy grinding job. In that case maybe I can find a fascia to cover the edge and clean it up a bit?

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Big Ed

N50247 - '79 Super D
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On a side note, found a mystery sender. It is installed at a T fitting inline on the tube carrying oil to the oil pressure gauge. Haven't tried to trace the wires. Any guesses? Mine is that it turns on the hour meter. In which case that is a hell of a reason to yank out the hour meter and replace the oil pressure gauge with an electric gauge.

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Bartman

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@#-$+&_**&!!!

Got the new Mitchell gauge. It is 2 1/4". Tried it out and realized the old SW gauge and panel hole are 2" even. There is very little excess material between the gauges, and between the gauge and edge of the panel. Little room for error when cutting a larger hole.

Aggravating for 2 reasons. First, ACA had a replacement capillary tube and bulb for the old gauge for 90 bucks. Second, I am running out of time to get my aircraft out of annual and make my planned timeline to Oshkosh. Only 5 work days left.

So now I am left with 2 bad choices. A) Have the A&P hack away at the panel trying to fit the electrical gauge, or B) lose 2 more days having the analog sensor overnighted from Wisconsin.
if you can clamp a block of wood behind the panel, and if you can spin a hole saw fast enough you might be able to get an ok cut with a 2 1/8" hole saw. if you were closer I'd drive over with mine. a fly cutter is out of the question, imho, with a hand held drill. a dremel tool or die grinder would do a nice job but you'd really have to control where the filings are going so they don't end up scattered all behind the panel.
 

Big Ed

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Went in this morning and my A&P had already installed the sensor and run the wire. He's not too stressed about the gauge hole, so I think we'll go with that. He said he would enlarge it with a file, which sounds like a chainsaw for cosmetic purposes. If I don't like the results, I'll look for some kind of plastic face plate with 4 screw holes and a nice clean 2 1/4" cutout.
 

Bob Turner

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I remember setting my panel up for standard 2 1/4" instruments, then making an adapter for the SW gauges.