heat hand----very strange

[1991hb]

I was out tonight driving around and on my way home I noticed that my heat hand would drop all the way down and then back up to normal position. It did it quite a few times but it never once went up like it was over heating. This is the first time I have ever noticed it doing this and there is no check engine light either. If you need to know it's a '91 hb with a d15 block and y8 head. Any Ideas? Thanks

 

[hosmer]

temp sensor is shitting the bed maybe...?

 

[BlueCrxNC]

You'll never get a check engine light for the Temp Sensor. The cluster gauge uses a seperate sensor than the ECU. Either the sensor is going bad or you have a wiring issue (Corrosion causing partial wire break/loose connection, problem with gauge itself, etc.)