The International Cessna 170 Association

frasergu wrote: Thank You, we installed a 5/8 NPT plug there with the copper gasket you have provided the information for. This sealed the engine for transport to and from the engine test stand after overhaul. There was an o-ring in there when I took it apart, and then it was lost. Maybe that is why the previous owners had so much oil leaking?
Thanks
GC Fraser

The synopsis is this: Prior to 1998 Scott used oil temp probes with a bulb which inserted into an adapter-nut, and the bulb had a flat flange (integral copper) which matched the flat flange bed inside the adapter nut. The adapter nut is what screws into the engine using a copper crush gasket. (PN AN900-10)

After 1998 Scott changed the flange on the bulb to a flared (conical) flange, which requires that the older adapter nut not be used... instead a matching, internal, (conical) flared-flange adapter nut must be used. In every case, the AN900-10 crush gasket fits between the adapter nut and the engine.

NO gasket or O-ring is used between the bulb and the adapter nut. A snug fit is all that's required. (In fact, if you overtighten the bulb-nut into the adapter nut you will shear the bulb-flange and create an oil leak...sometimes the leak being so big as to lose all the engine oil in the next flight.)

To reiterate.... you MUST use the correct bulb and adapter nuts which are made for each other or you will have a leak. DO NOT MIX THEM. You MUST use an AN900-10 copper crush gasket between the adapter nut and the engine.

I have what appears to be an original oil temperature gauge, p/n 0411017, with the Cessna logo on it. What's interesting is that the bulb style doesn't really match up with either Scott style; the nut end is flat where it contacts the capillary bulb and the bulb is flared where it contacts the adapter.

That may be an early Rochester unit made for Cessna. It also had a matching adaptor. (Original enthusiasts can have an instrument shop silk-screen the Cessna logos on any gauges.)