I just bought my first mustang! Dream car and waited till all the kids were grown 1986 Mustang Convertible LX - the radiator, water pump, and all the hoses were recently replaced as the car had been sitting a while. When driving, the temp gauge stays around the R to mid-M range. At times it creeps up to the far-M to the A, stays there for a few minutes, then slowly returns to the R range. It's driving my husband nuts. Not really sure where to start - it has been suggested that perhaps it had air in the lines since the cooling systems was all replaced or perhaps the thermostat. Before we start tearing into things, wanted to check for some advice. When the heater is on, it does bring the temp back down quickly so I'm thinking we are getting ok circulation. Any advice to look for would be appreciated!

 

any smoking? worse case blown head gasket...

 

no smoke - runs great! no raising temp when idling - we've had it idling for an hour and it didn't move a bit. The temp goes up to A when driving - whether or not we have the heater on - then it eventually kicks down on it's own. It's perplexing because it's not consistent and it does kick down eventually.

 

a new radiator will do wonders. that or try a lower temperature thermostat,.