id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
100601294,MDU6SXNzdWUxMDA2MDEyOTQ=,526,64-bit values are coerced to 32-bit when writing as NETCDF4_CLASSIC,6645714,closed,0,,,5,2015-08-12T18:06:42Z,2015-09-01T21:02:08Z,2015-09-01T21:02:08Z,CONTRIBUTOR,,,,"```
import xray
import numpy

ds = xray.Dataset()
time_data = numpy.arange(10.0, 100.0, .5)
raw_data = time_data.copy()
times = xray.Variable('time', time_data)
data = xray.DataArray(raw_data, dims=['time'], coords={'time': times})
ds['data'] = data
```

If you examine ds now, you’ll see:

```
<xray.Dataset>
Dimensions:  (time: 180)
Coordinates:
  * time     (time) float64 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 ...
Data variables:
    data     (time) float64 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 ...
```

Now, if we dump to netcdf and reload:

```
ds.to_netcdf('test1.nc', format='NETCDF4_CLASSIC')
ds1 = xray.open_dataset('test1.nc')
```

The formerly 64-bit values are now 32-bit:

```
<xray.Dataset>
Dimensions:  (time: 180)
Coordinates:
  * time     (time) float32 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 ...
Data variables:
    data     (time) float32 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 ...
```

It looks to me like coerce_nc3_dtype is being called for all formats that aren't straight NETCDF4.
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