[pepsiman50]

Hi everyone I have a 1986 civic crux si the temperature gauge will work properly when I let the car warm up in the morning but when I start driving it will fall down to cold and stay there I can feel heat coming from the vents but the gauge doesn’t move does anyone have a idea on how I can fix this issue I don’t want it to run hot on me thank you for your time on reading this

 

[Dave_Darling]

How's the thermostat? Is it present and operating correctly? Have you checked for air bubbles in the coolant or bled the coolant system?

Have you verified that the engine is running cool when the gauge says it is? Is the gauge actually correct?

--DD

 

[pepsiman50]

As far as I can tell the thermostat is working cause if I let it sit and warm up the gauge works like it should it goes up half way and stays there but when I start driving it drops to cold and barely moves from there as long as I’m driving

 

[bambbrose]

99% of the time this is the thermostat. Because you are driving there is air moving across the radiator which over-cools the coolant and the temperature drops. The gauge is reflecting this drop. The thermostat's job is to close off the radiator when overcooling occurs and it isn't able to do so in your case.

The heater only pushes out 90 to 100 degree air so there is a huge gap between the temps where a heater is functional and where we have proper coolant temp (~200). The thermostat can be faulty but the heater still functional in this temp range.

Start with a new thermostat.

 

[pepsiman50]

99% of the time this is the thermostat. Because you are driving there is air moving across the radiator which over-cools the coolant and the temperature drops. The gauge is reflecting this drop. The thermostat's job is to close off the radiator when overcooling occurs and it isn't able to do so in your case.

The heater only pushes out 90 to 100 degree air so there is a huge gap between the temps where a heater is functional and where we have proper coolant temp (~200). The thermostat can be faulty but the heater still functional in this temp range.

Start with a new thermostat.

Thank you I’ll start there and see what happens