Coolant temperature gauge wonkiness

Fellow Audi-ophiles,
I'm driving a US spec 1998 Audi A4 V6 Quattro, and just today my coolant temperature gauge starting falling to C once it had reached
normal temp. Then it suddenly popped back to normal.
Sometimes it is normal after the car is started, then falls back to C.
The radiator is hot, the coolant level is good, the fan is working, so I'm suspecting the sensor or a connection.
Any advice as to what to look for?
Thanks
--


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It is more than likely the sensor. You'll need to buy a new one as the sensor and gauge are matched.
Check the sensor, wiring connections, wiring and gauge. If you can get a second hand sensor from a car that is the same as yours it may when installed show, a lower/higher reading, if the reading is steady that it is the sensor that has malfunctioned. If it is the sensor then you need to buy one. The sensor and gauge are matched. Another sensor can work but the reading can be lower/higher. If when you put in a known good sensor and you know the wiring is good and the gauge raises and falls then it's the gauge that's malfunctioned. If you know the sensor and gauge are good then it's the wiring that is damaged. Air in the coolant and a collapsed coolant pipe, sticking thermostat may also cause the gauge to fluctuate. I do not know about your car. Mine is a 1996 A6 1984 cc 4 cly engine which has 2 sensors one for the gauge and one for the computer. Getting to to the gauge is a long job.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

This happened with my RS6 a few years ago. I had it fixed at an Audi shop - wasn't expensive. I think it was in the sending unit, but not sure.
Dave A8L
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 5/19/2011 8:31 PM, Paul Dhuse wrote:

Almost certainly the sensor. I've had several replaced. Here's a DIY article:
http://www.audiworld.com/tech/eng108.shtml
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 20 May 2011, Paul Dhuse wrote:

I had a 1986 4000CS quattro where the coolant temperature rose to normal, and then fell down towards C. If I slowed down, or followed someone closely, the temperature rose. It then fell again if I was in clear air. Solution was a coolant flush and refill.
Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.