89 100, coolant temp sensor

[David Conner <conner@cfm.ohio-state.edu>]

The coolant temp gauge in my 89 100 has been erratic for a long
time...mostly not working at all, with intermittent mood swings where it
will decide to tell me the temperature.
I assume this is due to the often discussed coolant temp sensor having "gone
south".

Where is the sensor for the gauge?  There seem to be three to choose from.
Is it the one in the radiator below the lower radiator hose?
If so, it looks like I'll have to remove the radiator hose to get it out,
draining the coolant.
What are the odds it's just crudded up and needs to be cleaned?

I don't want to have to remove it twice since it looks like I'll be draining
the coolant to get it out.  Since a new sensor probably couldn't be
returned, I want to be sure I'm getting the right one and that it indeed
needs to be replaced, not just cleaned up.

I know there are some of you who have dealt with this problem, so what
sayeth you?
Any help will be appreciated.
Dave Conner, Columbus OH   
conner@cfm.ohio-state.edu   
 '87 5KS, '89 100