Phil,
   It may be a crack forming around the sensor. Tightening only makes it
worse until the crack goes all the way around and the top breaks off.
Coolant geyser! I recommend replacing the reservoir while your at it. It
comes with the sensor and you do not have to drain the system. Pinch of the
hoses going to it.
Ken Lewis
86 Transporter Crew Cab
60 356 T-5 Porsche
http://neksiwel.20m.com/
Vanagon tech, pixs, O2 monitor gadget
----- Original Message -----
From: "Walker, Phil" <Phil.Walker@BROOKS.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, July 27, 2004 11:56 PM
Subject: [VANAGON] Friends on the road - coolant leak - need some advice

>.....He called me tonight from camp and it seems as if he's got a leak from
the sensor on the coolant res (not the overflow). I'm guessing it is just an
o-ring fix.....