The International Cessna^® 170 Association

My new Rochester gauge indicates low. A 225 degree bath indicates about 222 on the gauge and a 240 degree bath indicates about 235 on the gauge. This test was conducted in a large, well equipped metrology lab with calibrated gear and a knowledgeable technician. The results were a bit disappointing so I called the manufacturer who sent me the generic calibration sheet. The cal sheet states a 230 degree bath should indicate 230 degrees plus or minus 11 ½ degrees – Wow! I guess 5 degrees low at 240 is not so bad after all…
JP

So 2 degrees off at 225 and 5 degrees off at 240. 2 degrees doesn't seem so bad, although you would expect it to be right on, but 5 degrees off at 240 seems not so desirable. 11 1/2 tolerance seems to be too wide to me, but I am not a technician. I have that same gauge in my panel and I know it has been in there for at least 26 yrs. I just purchased one of those long probe meat thermometers and plan to test my oil temp with it the next time I fly. We see George and others suggesting we check the accuracy of our gauges. Would be interesting to see how many gauges, especially the ones like yours with the actual temp indicators, are right on or are off by who knows how many degrees.

Considering the technology in that probe, that's pretty good. If you want +/- 1 degree accuracy across the scale, you'll have to add at least one zero, just to the left of the decimal point, to what you paid for that gauge, BEFORE you start on the approval process.

All things considered I think this gauge will work fine. At least I know that an indication of 235 represents about 240 degrees, my summertime, 50 weight, red-line.
My technician and the manufacturer both state these gauges are not adjustable. You get what you get...
JP

I forgot to mention I found a piece of Baffel seal missing which I think contributes to my elevated oil temps. It's way up front on the leading edge of the "Baffel assembly - top crankcase". It's Item 72 on the image. It looks like a lot of air could be lost due to this missing seal.

The gauge is within specs so it's legal to use, but if you are a real OCD person... remember that MANY AIRCRAFT gauges have acceptable errors. For example, your COMPASS has a correction table to address the problem. Your altimeter is perfectly airworthy with up to a SEVENTY FOOT ERROR. Your airspeed is allowed almost 10 kts. Your VSI is allowed up to TWO HUNDRED fpm errors.

In other words... if it's that important to you, then make up a correction-table and post it. But TREND is more important than absolute accuracy in such matters.

The theory of flight is still only a theory.
The act of flying.... is not a science... but an ART.

gahorn wrote:The gauge is within specs so it's legal to use, but if you are a real OCD person... remember that MANY AIRCRAFT gauges have acceptable errors.

The theory of flight is still only a theory.
The act of flying.... is not a science... but an ART.

Well said George!

I went for a flight this afternoon with new oil temp gauge and missing baffle seal installed. Oil temp never got above 210 F. Woo Hoo!
Last weekend the same flight in almost identical conditions indicated HOT.
So how hot is hot? I think I'll ask my metrology buddies to check the old gauge at 225 F just to see... I suspect installing that baffle seal helped a lot.
JP