The International Cessna^® 170 Association

It's unfortunately a fact that these capillary gauges are not noted for consistently long life. They either last 20 years without difficulty...or they fail regularly...and without any sense to the equation at all.
Common failures are: loss of fluid in the bulb/capillary, loss of hysterisis stability in the diaphragm, and failure of the needle bearings in the movement itself. Vibration, humidity, and rough handling seem to be the biggest enemies.
It's usually cheaper to just buy a new gauge and install it rather than continue to "monkey" with a bad gauge. There also seems to be little/no quality difference between the $90 Scott and the $25 Rochester gauges. (In fact, I'd not be surprised to find that Rochester makes the gauges for Scott.)

gahorn wrote: There also seems to be little/no quality difference between the $90 Scott and the $25 Rochester gauges. (In fact, I'd not be surprised to find that Rochester makes the gauges for Scott.)

The last Rochester gauge I bought (oil pressure) was stamped with white letters on the case "For experimental use only"
jc

Jr.CubBuilder wrote:My Scott gauge quit working, after I had been unable to fly for three weeks. I'm hoping the needle is just frozen, any suggestions besides the boiling liquid? I've still got a few hours before an oil change is due so I would prefer not to pull the probe out till then if I can get away with it.

Late last summer, I noticed that my oil temp gauge never indicated above about 180-ish, when I knew from previous experience it shoulda been reading in the 200-210 range. I had the same thought- just a sticky needle. I figured I'd replace the gauge, then free up the needle on the old one & keep it for a spare. When I was testing/calibrating the new gauge, I dunked the probe from the old one into the boiling water- it climbed rapidly to above 200, then went right back down to the 180-ish position. Did this several times, same result. Jr, you're better off just ordering a new gauge from Spruce- mine was $81 delivered last fall. Then if you do free up your "frozen needle", you'll have a spare gauge (but don't count on it).

Eric

Yeah I guess you're right Eric. I was poking around under the cowl, and briefly behind the panel all the while getting that sinking "this is a royal pain in the ass" feeling. $75 doesn't seem like that big of a deal the more I look at it.

Jr, did you get your oil temp gauge squared away yet?
I was re-reading this topic, and John, I was wondering why you decided to test your gauge at 280 degrees? That's way above redline even for modern oil (245), personally I wouldn't have figured the gauge was good for that much. Besides, I would want to test at the approx operating temp (200-ish), and maybe also at redline (225 or 245), it seems like that's where you'd want to know that the gauge is indicating true.

Eric

zero.one.victor wrote: I was re-reading this topic, and John, I was wondering why you decided to test your gauge at 280 degrees? That's way above redline even for modern oil (245), personally I wouldn't have figured the gauge was good for that much. Besides, I would want to test at the approx operating temp (200-ish), and maybe also at redline (225 or 245), it seems like that's where you'd want to know that the gauge is indicating true.
Eric

My (slightly flawed) theory was to heat the oil to 280, bring the oil back into the hanger, put the probe in the oil and watch the thermometer. When the oil cooled to 240 I was going to mark the gauge. Seemed like a good idea at the time, but didn't work out due to the reasons mentioned above. My gauge returned to normal after a few flights, but I will be installing a Scott next oil change.

jc

gahorn wrote:.......... There also seems to be little/no quality difference between the $90 Scott and the $25 Rochester gauges. (In fact, I'd not be surprised to find that Rochester makes the gauges for Scott.)

My Spruce catalog lists the Scott gauge (p/n RN-2100) at $73.95, the equivalent Rochester gauge (p/n 10-11600) is listed at $61.75. The Rochester oil pressure gauge is the cheapie: Scott p/n RN-2550 is listed at $67.95 while the equivalent Rochester (p/n 10-22302) is only $33.20.

Eric

zero.one.victor wrote:

gahorn wrote:.......... There also seems to be little/no quality difference between the $90 Scott and the $25 Rochester gauges. (In fact, I'd not be surprised to find that Rochester makes the gauges for Scott.)

My Spruce catalog lists the Scott gauge (p/n RN-2100) at $73.95, the equivalent Rochester gauge (p/n 10-11600) is listed at $61.75. The Rochester oil pressure gauge is the cheapie: Scott p/n RN-2550 is listed at $67.95 while the equivalent Rochester (p/n 10-22302) is only $33.20.

Eric

I was actually quoting (with perhaps poor memory) from an old Wag Aero catalog. The latest Wag Aero lists the Rochester at $39 and the Scott at $73 (oil temp gauges.) The Rochester oil press guage (in WagAero) is listed at $24, while the Scott press. gauge is $68. In all fairness to Scott, their gauges are FAA/PMA. I talked to Rochester and they admitted making gauges for Scott. (They do not claim their identical gauges are PMA'd, and I've examined the two different brands disassembled and could not see any obvious differences. Of course, being the exacting kind of guys we all are, we only use PMA'd (or STC'd) gauges, unless we've determined some other basis of approval.)

As a follow-up, I just replaced my oil temp gage and got a pleasant surprise. My oil temps dropped 20 degrees. I checked the new one in boiling water before installing. When I put the old one in the boiling water it it pegged at the top of the red. I am now running @190 - 200 degrees on an 85 degree day. It is a warm - fuzzy feeling to be comfortably in the green.

N2865C wrote:As a follow-up, I just replaced my oil temp gage and got a pleasant surprise. My oil temps dropped 20 degrees. I checked the new one in boiling water before installing. When I put the old one in the boiling water it it pegged at the top of the red. I am now running @190 - 200 degrees on an 85 degree day. It is a warm - fuzzy feeling to be comfortably in the green.

This is what I've been cautioning folks about for over a year now. There seems to be a popular belief that when these gauges fail they read low. But I've noticed that in many cases (including my own gauge) they read HIGH as they grow old and fail. I suspect it has to do with hysteresis. (the bourdon-tube capsule takes a "set" and reads excessively high due to relaxation of the tube. Just a theory.)