The International Cessna^® 170 Association

I'm pretty sure I understand how the oil temperature gauge works. The system (bulb) is closed and filled with a fluid which expands moving a diaphram and then the needle in the gauge.

So tell me this. How is it that my gauge has become intermittant since reinstalling my rebuilt engine? The gauge will show no temperature for as much a 40 minutes into a flight then spring to life and work flawlessly for the rest of the flight and day.

The EGT (single probe) on the other hand works for the beginning of the flight but after about 10 minutes dies off to nothing. What up with that?

I have an Alcor EGT probe/gauge, and it's operation
was intermittent until I pulled the thing apart and
cleaned all the exhaust by-products / corrosion off
of it and re-installed it.

I also recently installed a PMA'd Scott oil temp gauge
(to replace the original Cessna unit). The original Cessna
gauge worked fine, but the probe & nut had excessive
wear from years of oil changes and over-torquing the
probe securing nut. Anyway, initially, my Scott gauge
would do the same thing you're describing (i.e., not do
anything for the 1st few minutes of flight, then all of a
sudden, spring to life). It works fine now, but my thoughts
are:

1. There is "air" ine the line somewhere (unlikely with my
new gauge & probe, all came as an assembled unit)

2. The gauge/needle mechanics are sticking on the low end
of the scale somehow (might float as an explanation to my
problem with a new gauge, but not with yours, as, I assume,
you had the engine rebuilt but retained the stock/original oil
temp probe + parts).

The capillary type gauge is not a precision or jewelled movement. It likely has a sticking needle.

Bela, it wouldn't be air in the temp gauge system. Your thinking about oil pressure.

George I'll go with the sticking gauge as it sat in the low position for 7 months. Do you know of any way to clean the gauge with out sending it out?

My understanding is there is alcohol (or something like that)
in the oil temp capillary line. If that assumption is correct,
then air in the line could cause erratic indications, no?

OK Bela but how would the air get in?

Hairline crack in the capillary tube and/or fitting?

Bela if it had a hairline crack then it would never build enough pressure to move the gauge.
I'm thinking more in linewith George that the movement is sticking.

Something else you may want to look for is the possibility of kinks or sharp bends in the capillary since you noted the problem started just after installation of the engine.

N9149A wrote:Bela, it wouldn't be air in the temp gauge system. Your thinking about oil pressure.

George I'll go with the sticking gauge as it sat in the low position for 7 months. Do you know of any way to clean the gauge with out sending it out?

Take a thin bladed screwdriver, or knife blade and slide it under the rim of the lens retainer to pry it open. Remove the glass. (Some suggest a cheap suction cup for this, but I've never found it necessary.) Examine the needle pivot closely. You may find it interfered with by the dial face (black, numerically marked dial face) especially at the pivot.
Look for such interference. If none found, gently remove the dial face and slide it past the needle to remove it from the instrument. Examine the backside/interior of the gauge chamber for dirt/dust/junk/etc that may interfere with the needle movement.
Correct any deficiency. (great time to "calibrate" the gauge by bending the actuating arm of the needle.)
Reverse the process to reassemble.
Sign off the gauge overhaul with your certificate number.

gahorn wrote: Sign off the gauge overhaul with your certificate number.

Just wanted to clarify your are kidding about the sign off.

Oh, No! I'm not kidding. ALL maintenance performed on an aircraft must be recorded in the permanent maintenance records! (You don't HAVE an instrument repairman's certification? Ooops. You'd better not do this work yourself then. You'd better get an instrument shop to do it. It'd only cost about twice what a new gauge sells for.)

(Note to Everyone: This tongue-in-cheek exchange between Bruce and I is merely my convoluted sense(less) humor. I am fully appreciative not only of Bruce's wealth of knowlege about these airplanes, but also of his correct appraisal of and advice regarding this questionable repair-scheme. While it might correct the faulty gauge inexpensively, simply, and might also be enjoyable to the owner-tinkerer.....it IS NOT FAA-approved procedure. Which is Bruce's point.) Caveat.

Bruce, did you ever get your gauge squared away? I just recently noticed that my oil temp gauge was still indicating winter-like temps (150-160ish) and here it is August! After my last flight, I crawled under the panel & gave the gauge a few light raps with my ball-peen. If that didn't do the trick, I might have to exercise the privileges of my instrument repairman's certificate & see if there's something inside the face of the gauge keeping the needle from going to it's normal summertime indication of 200ish. I was wondering if you'd had yours apart, & if you had any tips.

Eric

Well "officially" it's working just fine. The temp gauge will spring to life sometime in the first 10 minutes of flight and act normal there after for tne rest of the day.

I've let my "repairmen" certificate lapse so for now at least till I renew it, I'll only look at the gauge when it's working.