I'd still replace it asap, especially with summer coming. What if one day while flying over the Cascades, you hit some moderate bumps, and it starts reading 240???? Yikes.

Z

The problem could be something as simple as a bad ground. Corroded ground contacts are a frequent source of trouble for older airplanes, and really not that hard to check. I'd look there first before replacing the gauge.

I was thinking that the power would loop through the probe back through the gauge to ground with the gauge measuring the difference in voltage to and from the probe...could be wrong though. Look to see it there's a ground wire running from the gauge to frame ground. A needle buried at the bottom would indicate an open circuit to me.

Come on Junior, hopefully you know (or will soon find out) that you have a mechanical (capilary tube- with probe,not sending unit) oil temp gauge, NOT an electric gauge. You can ground or unground that thing until the cows come home & it wouldn't make a bit of difference.
The different style of flange on the probe nut must match the seat in the adapter bushing that screws into the oil screen or oil-filter adapter. When I bought a new Scott gauge last year they sent a new adapter bushing with the new styl;e seat, but did not point out that it was different. You can (& eventually will) damage the flange on the new probe if you install it into an adapter bushing with the old-style seat.
There's some posts about this on the 170 site.

Eric

Jr,

You can say SHIT around here, no punctuation.

BTW, that is a really sweet pic of Brown Whisky by the windsock.

Z

A capillary style gauge, DOH!, should have thought of that. We had a capillary type temp gauge on an Aeronca that I was a partner in. I never really thought twice about it. What goes caput on that type of gauge?

In my old '72 Volvo the heater thermostat was just a capillary tube going from the internal heater core to a valve on the main coolant system. Classic technology.

Z