Have a 1992 4 cyl tempo when idling the temp gauge registers and I get heat.
When traveling down the road the temp gauge goes to cold and I no heat, this happened after I replaced the thermostat prior to that I was getting minimal heat.

 

I figured out what the problem was, the new thermostat was defective

I guess you get what you pay for this is the second time I received a defective part from this large auto part chain.

 

Thanks for the update..

Might search out a new place to get your pieces

 

....please tell us which brand we should avoid.

Thanks