The Cessna 120-140 Association Forum

Greetings,

The oil temperature need is stuck in the mid green arc regardless of the outside air temperature.
The last time I flew, the OAT was 18 degrees. Usually the oil temperature does not register at all.
However, the needle stood at mid point in the green arc.

I checked Aircraft Spruce for a replacement. The only TSO, FAA PMA approved temperature guage is a
Mitchell electric oil temperature guage (100-250 F)

The mechanical guages are NOT... TSO, FAA PMA approved.
Are there any other sources for a direct replacement?

Would appreciate any recommendations to report to my mechanic.
Thank you.

Guy M Naples
Member # 1114
740-803-1161 (please leave message if I do not answer)
GCJLNAPLES@CS.COM

Cessna 140
N89380
C-85-12

Read the following, from our good friends over at the International Cessna 170 Association.

Our airplanes were produced under CAR4 (my fellow good moderator John Cooper will correct me if I’m wrong) when TSO didn’t exist. Take a look at the posts from the C-170 group which explains TSO requirements pretty well.

https://forum.cessna170.org/forums/view ... hp?t=10685

Thank you for the Cessna 170 discussion re TSO. Very helpful.

To your specific question, the Rochester oil temp gauge sold by Aircraft Spruce is the equivalent gauge to the original. I think it even bears the same or similar part number to the one listed in the parts manual. Over the years many original gauges have been replaced by the Scott version, but I don't think they are available any longer. Personally, I would replace it with the one from ACS and sign it off as equivalent to the original.

Another tack: there are, or used to be, shops that can repair your original (assuming it is original) but there isn't that much demand for old mechanical oil temperature gauges...

I think you could make an argument for replacing it with a newer, TSO'd electric gauge, like the Mitchel. I used to sell a lot of them and I'm sure it wasn't so they could have it on the shelf.

In the end it's on the installing A&P to sign it off, with or without further approval. Check AC23-27 Vintage Part Substitution for more confusion.

As a side note, I purchased the Rochester gauge from Spruce a few years ago and thought I'd better test it before installing. I put it in boiling water which should have read about 210 deg at my elevation and got a reading of 190, which is obviously an error in the worst direction. Spruce was fine with exchanging it and the new one came in at about 208 which was good enough for me. It's worked fine since. Anyway I strongly recommend testing before installing in case that same QA guy at Rochester is still there.

For repair to the OEM stuff, contact Keystone Instruments, Lock Haven PA, info on their web page, been around for years, IIRC, they are an outgrowth from tne old Piper crowd when Piper moved to Fl many, many, many years ago! Excellent reputation.