At 02:37 PM 4/25/98 -0700, you wrote:

 I have decided to replace the coolant sensor  I have the sensor but
 have not installed it yet.  It doesn't have threads and appears to be
 held in place by a clip.  Is it possible to switch from old to new
 sensor fast enough to avoid spilling a lot of coolant,

yes, but do it while the engine is *cold*

 or is it necessary to drain the coolant from the block first?

no

 Is any form of sealant or O ring replacement needed??

sealant, no; O ring replacement, absolutely - applying a film of heavy
silicone grease to the  O ring enables it to seat smoothly & quickly.

>Alain Thibault

Austin