Temp gauge fluctuating
 

Temperature gauge is fluctuating relatively slowly, particularly after a longer drive. My wife drove the car to the city this morning (about an hour and a half drive at 55 mph), and she told me that the temperature gauge was at about 3/4 to H. It will read anywhere from about 3/8-5/8 normally, but I know it shouldn't be fluctuating much, if at all. Usually I can see it kinda creep up to around 5/8 when I'm coasting down to make a turn, then as I open the throttle again it quickly drops back down to around 3/8. Brand new ECT sensor and sender installed and system flushed when I replaced the head gasket about two weeks ago; thermostat, hoses, and radiator (came with cap) replaced a few months ago. Could it just be that I got a faulty part out of the box?

Make sure both cooling fans are engaging when temp reaches ~ 195F. A IR temp gun is handy for this.

If thermostat was not an OEM thermostat, suggest trying a replacement. I have had aftermarket thermostats control temperature poorly.

good luck

Both cooling fans are kicking on when the t-stat housing is at about 187-188 degrees F.

Did you use a Honda thermostat?

No. It was aftermarket. Went ahead and ordered OEM.

Install the Honda thermostat, then refill and bleed the coolant. Then report back if the problem went away or remains.

If this happens while driving, especially at highway speeds, don't bother looking at the fans. At 30 mph, there's already more air from the car's motion than what the fans can provide.

Instead, the thermostat is a better place to look. And don't forget to bleed out the air bubbles - bleed screw on the thermostat housing. Honda cooling systems don't like to have any air bubbles inside.

Put in the OEM t-stat a couple of days ago, and so far so good! The needle stays at a steady 3/8 under all conditions. Thanks again, guys!