Scary High Oil Temps - Lycoming 540

Lindberg said:
You know an awful lot of stuff. Did you know that?
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Not really. What I know is in a very narrow range of subjects. And I'm not a master at any of them.

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That green slice is really generous. None of us would have anything more than a tiny green slice's worth of the total body of knowledge. We just don't realize how little we know. And then there's the stuff we "know" that just isn't so, too.
 
Dan Thomas said:
Not really. What I know is in a very narrow range of subjects. And I'm not a master at any of them.

View attachment 131001

That green slice is really generous. None of us would have anything more than a tiny green slice's worth of the total body of knowledge. We just don't realize how little we know. And then there's the stuff we "know" that just isn't so, too.
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But we do appreciate the stuff that you do know and share here.
 
Dave Theisen said:
But we do appreciate the stuff that you do know and share here.
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Thanks. I lurk here and in the homebuiltairplanes.com forum, and that's it. I have little or nothing to offer in most other fields. I used to do boats, but that stuff outdistanced me long ago, as did electronics. I can fix some ancient, antique radios. Some ancient TVs, maybe, though I haven't fixed one of those in 40 years. I have no idea what goes on inside digital stuff, other than electrons are moving around inside it.

Airplanes use magnetos and carburetors and mechanical fuel injection and alternators and basic electric circuitry. Understandable stuff.
 
Dan Thomas said:
Not really. What I know is in a very narrow range of subjects. And I'm not a master at any of them.

View attachment 131001

That green slice is really generous. None of us would have anything more than a tiny green slice's worth of the total body of knowledge. We just don't realize how little we know. And then there's the stuff we "know" that just isn't so, too.
Click to expand...
PacMan' pie chart - for fun
 
Dan Thomas said:
Not really. What I know is in a very narrow range of subjects. And I'm not a master at any of them.

View attachment 131001

That green slice is really generous. None of us would have anything more than a tiny green slice's worth of the total body of knowledge. We just don't realize how little we know. And then there's the stuff we "know" that just isn't so, too.
Click to expand...
I had a physics teacher that described it as an onion. You start in the inside and each layer of knowledge you gain the larger the layer of knowledge you realize you don’t have. You also get to the point where you can’t expand the entire onion and specialize and only expand a section.
 
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Salty said:
I had a physics teacher that described it as an onion. You start in the inside and each layer of knowledge you gain the larger the layer of knowledge you realize you don’t have. You also get to the point where you can’t expand the entire onion and specialize and only expand a section.
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An educated man told me that someone with a Bachelor's degree knows a little about a lot. The Master's means he knows more about less, and the Doctorate means he knows a lot about almost nothing.
 
Update? Did you solve the problem?? Will you be able to fly to OSH?
 
Larry Korona said:
Update? Did you solve the problem?? Will you be able to fly to OSH?
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The new Oil Temp probe arrives tomorrow. If that doesn't solve it, I am flying Delta.
I replaced the Oil temp gauge and I put the probe in boiling water and it read 260. That leaves the probe.
I will be purchasing an engine monitor at Osh this year. I don't want to but clearly I have spent $2000 fixing what may be a $125 problem here.
 
SixPapaCharlie said:
...but clearly I have spent $2000 fixing what may be a $125 problem here.
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A common outcome with electrical problems.

There should be a separate certificate for mechanics who understand and can troubleshoot and quickly fix electrical issues. Every mechanic is supposed to be able to do it, but this is clearly not so. Pilots need additional ratings to fly twins or at night or in IMC, and I think mechanics similarly need more training and certification in some areas.
 
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Dan Thomas said:
A common outcome with electrical problems.

There should be a separate certificate for mechanics who understand and can troubleshoot and quickly fix electrical issues. Every mechanic is supposed to be able to do it, but this is clearly not so. Pilots need additional ratings to fly twins or at night or in IMC, and I think mechanics similarly need more training and certification in some areas.
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And yet the common solution is to add more electronics, such as an engine monitor, when the electrical problem can't be figured out. Makes total sense, ha.
 
I am still nowhere.
Replaced the gauge and the probe.
Replaced the wire running from the probe to the gauge.

Ran the plane until it was pegged today. Shot the IR thermometer at the probe, oil filter, etc nothing above 190

My MX and I are scratching our heads. He is starting to wonder if too much voltage is going to the gauge. There is a strange little diode that he wonders if it is to reduce voltage so it isnt taking the full voltage.
I think it keeps the current from going the wrong way but we are grasping at straws.

I just threw in the towel and bought a plane ticket to Osh.
I am going to look at the EI CGR30 while I am up there. That seems like the most bang for the buck price-wise and also being a primary instrument.
I want to get all of this 50 year old trash out of the plane. I can't afford to buy the engine monitor but it seems I also can't afford not to.
 
brcase said:
This is when you start getting return on the $$$ invested in one.
How much have you paid the mechanic already trying figure this out.

Brian
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$750 for the oil cooler parts and labor
$600 for the Vernatherm that I didn't need - parts and labor ( He also fixed some baffling and replaced some brackets that were cracked.
$150 for the replacement gauge that I didn't need
$135 for the replacement sensor that I didn't need
$125 for the test gauge I bought from Spruce to confirm the oil isn't actually 260 degrees. I accidentally broke it so its in the trash now.

So about $1,800 to have solved zero problems.
The Oil cooler was on the verge of erupting so that was indeed needed. Would have been an emergency soon.
 
SixPapaCharlie said:
$750 for the oil cooler parts and labor
$600 for the Vernatherm that I didn't need - parts and labor ( He also fixed some baffling and replaced some brackets that were cracked.
$150 for the replacement gauge that I didn't need
$135 for the replacement sensor that I didn't need
$125 for the test gauge I bought from Spruce to confirm the oil isn't actually 260 degrees. I accidentally broke it so its in the trash now.

So about $1,800 to have solved zero problems.
The Oil cooler was on the verge of erupting so that was indeed needed. Would have been an emergency soon.
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That sucks. I'll have a free beer for you in HBC if you wanna drop by. The good thing is you're not telling us you need a $50K engine rebuild...
 
Dan Thomas said:
If your gauge has the resistor, it may have broken down with age. Those old resistors were just a tiny carbon slug with wires at each end, encapsulated in a clay or phenolic covering. Vibration, heat and corrosion all take their toll, and a failing resistor would put the gauge indication way high.
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SixPapaCharlie said:
He is starting to wonder if too much voltage is going to the gauge. There is a strange little diode that he wonders if it is to reduce voltage so it isnt taking the full voltage.
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Are you sure it's a diode? Are you able to contact the OEM/spruce for instructions/diagrams/support?
 
kyleb said:
That sucks. I'll have a free beer for you in HBC if you wanna drop by. The good thing is you're not telling us you need a $50K engine rebuild...
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I'm scared to death that's what a new engine monitor's going to tell me
 
No I don't know what a diode or a resistor or anything is. My knowledge of electronics stops at capacitors cuz I have to replace them in my AC units frequently


It's this thing...

20240712_165252.jpg
 
The only thing though is that electronic component is on two poles of one of the fuel gauges. It's not directly on the oil temp gauge. That said these things do all appear to be Daisy changed together for lack of a better term
 
That is a resistor. Now you gotta figure out if it's
a) working (easy to check with a multimeter)
b) the correct value (see install documentation)
c) wired correctly (see install documentation)...

en.wikipedia.org

Electronic color code - Wikipedia

en.wikipedia.org en.wikipedia.org
 
Retrieved it from the plane. Going to test it with my multimeter. I wish there was a part number written on it.

20240712_202821.jpg
 
The good news is that the infrared thermometer is telling you it's an indicator problem, not excessive oil temp from an engine problem..

Call the good folks at Air Parts of Lockhaven. They are the wizards when it comes to Comanche instruments. Maybe they can give you some helpful guidance.
 
Chip Sylverne said:
The good news is that the infrared thermometer is telling you it's an indicator problem, not excessive oil temp from an engine problem..

Call the good folks at Air Parts of Lockhaven. They are the wizards when it comes to Comanche instruments. Maybe they can give you some helpful guidance.
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I called them today and they said just send us the gauge and we'll rebuild it. I've heard really great things about them but this kind of felt like a hammer sees everything as a nail situation.

Also it was 4:50 on a Friday so I don't blame her for being a little short with me
 
SixPapaCharlie said:
I am not smart enough to understand that article. I tried really hard.
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Curious. How do you plan to test it with your multi meter if you don't know what the result should be?

Here's the secret decoder ring. It's 820 ohms if you don't want to try any harder.
resistorcolorcodecalc.com

Resistor Color Code Calculator

The Resistor Color Code Calculator identifies the value and tolerance of a color coded resistor given its bands colors. Supports resistors with 3, 4, 5 and 6 bands.
resistorcolorcodecalc.com resistorcolorcodecalc.com
 
mondtster said:
Curious. How do you plan to test it with your multi meter if you don't know what the result should be?

Here's the secret decoder ring. It's 820 ohms if you don't want to try any harder.
resistorcolorcodecalc.com

Resistor Color Code Calculator

The Resistor Color Code Calculator identifies the value and tolerance of a color coded resistor given its bands colors. Supports resistors with 3, 4, 5 and 6 bands.
resistorcolorcodecalc.com resistorcolorcodecalc.com
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I don't know I've only ever used a multimeter before to tell if something was connected to something else. It makes that beeping noise if electricity flows from one probe to the other.

Maybe there's a setting on the multimeter where I touch one side of the resistor and the other side of the resistor and it makes a buzzer sound
 
SixPapaCharlie said:
I don't know I've only ever used a multimeter before to tell if something was connected to something else. It makes that beeping noise if electricity flows from one probe to the other.

Maybe there's a setting on the multimeter where I touch one side of the resistor and the other side of the resistor and it makes a buzzer sound
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You posted the photo of your meter connected to the resistor while I was typing that. Look at the display on the meter in the photo, it is showing 850 ohms, which is well within tolerance for that resistor. In other words, it is fine.

As an aside, I don't think it has anything to do with your oil temperature gauge if it was strapped across the posts on a fuel gauge.
 
mondtster said:
You posted the photo of your meter connected to the resistor while I was typing that. Look at the display on the meter in the photo, it is showing 850 ohms, which is well within tolerance for that resistor. In other words, it is fine.

As an aside, I don't think it has anything to do with your oil temperature gauge if it was strapped across the posts on a fuel gauge.
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I kind of wondered about that too.
I think the next step is just to have a engine monitor installed
 
SixPapaCharlie said:
I think the next step is just to have a engine monitor installed
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Depending on your long term goals with the aircraft you may consider an intermediate option such as an Aerospace Logic oil pressure and temperature combination gauge as a fix. In the long run, eliminating all the old instruments is probably in your best interest for ongoing supportability as these aircraft aren't getting any newer.

SixPapaCharlie said:
Or land the plane with the gear in the up position
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That is an option that has worked for some!
 
Have to jump in here... (long time lurker first time poster)

I don't think that's an 820 ohm resistor, its 520 ohm. Bands are read left to right with these older resistors the banding is grouped to one side. You never start with a metallic band :)rockon:); the metallic is the tolerance band and is always on the right. So the green is 5, red is 2, the brown is the multiplier so x10, with the silver being the tolerance of ±10% for the total resistance of 520 that could read as little as 515 to as much as 525 ohms.

I suspect this is part of a voltage divider circuit... the gauge likely can't take the full 12 volts or it would peg the needle. Instead the temp probe, which is a variable resistor, is wired to this known fixed resistor in a voltage divider circuit to drop the voltage to an expected amount. I dont know what the rating of the probe is and couldn't find an electrical schematic after a few drinks tonight but for giggles let's say both resistors were supposed to be 520 ohms, this circuit would drop the 12 volts in down to 6 volts out. If one of these 50 year old resistors started to fail and increased to 850 ohms then that 5 volts is now 7.445 volts. If the gauge was expecting one thing at 6 volts but now was getting 25% more juice then things could read incorrectly.

Everything in that temperature circuit should have a known value to it found in a schematic somewhere. Just needs to be checked off one by one. It would be dumb but cool to buy a fancy new shiny when a 5 cent part would have fixed it.

Love your videos dude, keep it up and have fun at OSH. Told my wife about your bit about shoving the money in to fix the problems and it was the first time she didn't say 'and that's why we dont own a plane' so I'm thinking there's a chance...

Cheers - Brian


voltage-divider-main-circuit.jpg
 
SixPapaCharlie said:
…
$150 for the replacement gauge that I didn't need
…
$125 for the test gauge I bought from Spruce to confirm the oil isn't actually 260 degrees....
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I get the frustration. If I understand this correctly, you are still using the original guage, correct?

You have independently verified the original gauge and/or probe is providing and/or displaying inaccurate information in a controlled environment. I wonder what you were using to generate 12v at home because that’s a variable, but if a sensor/indicator combo works in a controlled environment and not in another environment, it’s either a power, sensor, or indicator problem.

I’m all for the engine monitor for a bunch of other reasons, but it does nothing to get you back in the air anytime soon. Isolate the problem to sensor, gauge, or power.
 
That 820 ohm resistor is good, you just have your VOM one scale too high. Depending on which probe you have installed, it may be your problem.
 
Cursory googling suggests that folks have had to calibrate things depending on the gauge and probe combination:
comanchetechtalk.com

Oil Temp Indicator/Probe Issues

Oil Temp Indicator/Probe Issues by David Pfeffer » Mon Sep 30, 2013 5:41 pm Hey guys- Troubleshooting a low oil temp indication (isolated to indica...
comanchetechtalk.com comanchetechtalk.com

I found one apocryphal post that mentioned an _82_ ohm resistor:
comanchetechtalk.com

AC Part crossover number for Oil Temp Sender

AC Part crossover number for Oil Temp Sender by Gomer Pound » Fri Jul 22, 2016 4:06 pm Hi, does anyone know of the AC part number for Piper 462-046...
comanchetechtalk.com comanchetechtalk.com
 
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