my 91 civic dx temp gauge red lines until i rev real high.i have replaced the rad,therm,all hoses and water pump works fine.the heater blows hot.the upper hose is hot and the lower hose is warm.def temp difference.my radiator res is at normal levels before and after engine warms up.when i replaced the thermostat there was what looked like gelled antifreeze.flushed the engine and all works well.i have been told to replace the coolant temp sensor.just looking for a second and third opinion before i replace.thanx.

 

Is the radiator itself staying full? Check when cold before each trip. When you remove the radiator cap it should be full to the top, no air space. Don't just check the reservoir.

Overheating only when the car is sitting still, that goes down when you start to drive, is typically because the fan(s) don't work. The car moving forces air through the radiator even without fans.

 

Did you bleed your coolant system as per the book. My 90 Civic would act up but only sometimes & it turned out that there was air in the system. A buddy of mine who is a mechanic told me these are really fussy when it comes to air. It took him an hour to get it bled completely. I think Honda says running it with cap off through 3 cycles of the fan he did 4 cycles.
Then as mentioned are you fans working.
If this is all good try the temp sensor.

 

O.K. I have replaced the temp switch,bled the system for air, and the radiator coolant level has not dropped.as i said everything else i can think of has been replaced and is working fine.temp gauge still jumps but it happens when i turn on my blinker or hit my brakes.it is making me think the gauge is shorting out somewhere.