  We present estimates of the signal to be expected in quiescent solar
conditions, as would be obtained with the COronal Spectrographic Imager in the
EUV in its coronagraphic mode (COSIE-C). COSIE-C has been proposed to routinely
observe the relatively unexplored outer corona, where we know that many
fundamental processes affecting both the lower corona and the solar wind are
taking place. The COSIE-C spectral band, 186--205 A, is well-known as it has
been observed with Hinode EIS. We present Hinode EIS observations that we
obtained in 2007 out to 1.5 Rsun, to show that this spectral band in quiescent
streamers is dominated by Fe XII and Fe XI and that the ionization temperature
is nearly constant. To estimate the COSIE-C signal in the 1.5--3.1 Rsun region
we use a model based on CHIANTI atomic data and SoHO UVCS observations in the
Si XII and Mg X coronal lines of two quiescent 1996 streamers. We reproduce the
observed EUV radiances with a simple density model, photospheric abundances,
and a constant temperature of 1.4 MK. We show that other theoretical or
semi-empirical models fail to reproduce the observations. We find that the
coronal COSIE-C signal at 3 Rsun should be about 5 counts/s per 3.1" pixel in
quiescent streamers. This is unprecedented and opens up a significant discovery
space. We also briefly discuss stray light and the visibility of other solar
features. In particular, we present UVCS observations of an active region
streamer, indicating increased signal compared to the quiet Sun cases.
