i already purchased a new thermostat, and gonna do an engine flush but i just wanna confirm something first.

I have a 91 CRX si, D16A1, i run the car for about 15-20 and the temp gauge raises up to normal. stays there till i start driving and then it dips down to below C.

will changing the thermostat and doing an engine flush help that problem? or is there something else going on here?

 

Do you have a thermostat in there right now?
How is the temperature outside when you see it drop like that?

 

Hope you went with a oem thermostat

 

Engine flush? Or coolant flush? I don't recommend a engine flush. Sometimes ruin motors. A coolant flush on the other hand should be done when you change the stat.

 

I'm running nto this same issue with my 88 dx. As soon as I start driving I guess the air flow cools things down too much.

I've also noticed that when this happens it stays In the high warm up idle.

 

Sounds to me it should be the thermostat and a good change of fresh coolant(50/50) should do the trick. And yeah open it up and see if you even have one, if you do its probly a safe fail one. Good luck