OK Honda Civic overheating problem. New thermostat, Perfect coolant 50/50 distilled, 10-w40 oil, ect.?

- is the cap broken: There should be a rubber gasket and a plastic nipple on the cap.

- Does it need to be flushed: Run the car with the RADIATOR CAP OFF(sorry for the caps but some people freak out when I tell them to do this), when the car warms up, test by keeping your finger in the hole touching the water, does the water shoot out. Shooting and slightly overflowing are two different things. If it looks like old faithful then the core needs to be flushed.

- Does the fan switch work: after running the car for a while does the fan come on?if not replace the sensor

- Did you relieve the pressure: You didn't specify the year of your civic, but older Honda's have a pressure relief valve you need to open when you fill it with coolant. Trace the top radiator hose to the engine, where it meets the engine if you see a bolt with a hole in the top, loosen it about a full turn (don't take it off) and fill the car with coolant. It will bubble at first, once the bubbling turns into a constant stream close it (carefully, its aluminum and over tightening WILL break it) that will get the bubbles out of the head so the pump can work properly

there are a host of other things it could be but those 4 are the most common, hope these help you.

BTW the gauge issue has to do with the heater, the heater in your car sends a signal to the gauge, basically I wouldn't worry about that

Honda Civic Coolant

Make sure you don't have an air pocket in the system by opening up the radiator cap, turning your heat on high, and letting the car run for awhile. If that doesn't solve it, check to make sure your cooling fan(s) are working, and also test your coolant temperature sensor.

Like the previous poster said, though, halfway isn't out of specs. Chances are, if your thermostat was bad before, it failed in the open position, and your coolant was constantly cycling through the radiator, instead of the thermostat opening and closing. Now that the thermostat is fixed, it is probably operating at normal temperature.

You have a circulation problem. The air gets cold because the coolant is not circulating through the heater core, and it overheats because the coolant is not circulating through the radiator. I would suspect you either have in internal problem with your water pump, or a blockage somewhere in the system. It stays cool when you are moving because the air is blowing across the motor, and the waterpump in moving at a higher RPM when the motor is at a higher RPM. A stuck thermostat could cause issues like this as well. I would replace the thermostat, and completely powerflush the cooling system. If that does not work, I would geive a close look at the waterpump. I have seen damaged impellers cause poor circulation.

First of all, I'd have the cooling system checked for clogs. If that shows okay, I'd replace the water pump. Water pumps do wear out. They still turn with the engine, but, the impeller blades get eaten away. No blades, no circulation.

If it does prove to be a clog in the cooling system, you should be able to have it flushed out. You might be able to do it yourself with a 'Flush Kit'. Just make sure that it fits your car.

really cant think of anything else but the sensor... does the fan turn on at all when it starts to heat up?

I may have not understood you right but if your temp gauge is halfway your good...