2002 ford taurus. Radiator overflows but, temp gauge not hot.

You may have a blown head gasket thatis pressurizing the coolant system-pull radiator cap off and put a pressure gauge on it and see if pressure goes above 17.5lbs-cheers Denny

If the thermostat is not opening, the engine will keep getting hotter as you drive. You could be low on coolant and have air pockets in the system which would cause the temp gauge to not be accurate. Is the radiator fan coming on when the tank is boiling ?

the fan will turn on when the engine temp reaches a set temperature and will only turn off when the engine drops below a certain temp and on the highway running hard it may stay on longer

First of all you have a bad heater core that needs to be replaced. Second you may have a bad temperature sensor. Make sure the radiator if full of water

There are 4 things you want to check in this order.
1. Make sure your fluid level is up to specifications.
2. Make sure the fluid is travelling through the radiator freely(water pump).
3. Make sure your thermostat is opening. This requires a great deal of caution, leave the radiator cap open (if it has one) and run the engine until the top radiator hose gets hot, If you have no radiator cap, watch for water rising or dropping in the overflow tank.Also watch for bubbles within the overflow or radiator.Also put all temp controls on high on the climate control center and feel for hot air once the engine reaches operating temperature(185-200 degrees). If you don't get heat within the regular time slot of 10-15 minutes you will need a new thermostat.
4. If you discover a large amount of bubbles within the radiator or the overflow tank than you've got a headgasket situation and should not drive the vehicle until necessary repairs are made. Thank you, Dana

It sound like there may be a small leak in the cooling system. You can check this by pressurizing the cooling system. You can buy a pressure checker for about 100 dollars. It will usually show up leaks that are small because you can pressurize the system cold and it won't evaporate.

check coolant level in overflow bottle and the radiator first.

check to see if temp blend door is rotating back and forth. Rotate temp knob while watching the motor that operates the blend door under the dash.

check to see if both heater hoses are hot where they go into the cowl in the engine compartment into the heater core. If not hot, check temp gauge to see if it reads nomal, if not replace thermostat.

Heater not working sounds like a blower motor or heating core. Make sure that your antifreeze is green and mix 50/50 with water, now check and sqeeze your hoses running from and to the Radiator and if its VERY hard and has a crunch sound, it's blocked up, use radiator flush and follow directions, If not than look into the Thermostat b/c if it needs repaired than it will stick and let enough fluid into the engine so that it does not overheat yet with the pressure will back up into the resevoir. My new thermostat is a 140 degree and i've never soon my temp meter get to half way after that.

is it possible it is your overflow bottle leaking or too full? If not These cars are bad about headgaskets. Start your car remove radiator cap and let it idle till it is up to temp and top radiator. If you have a leaking gasket or cracked head you would most probably see bubles and the water will try and come out of the radiator fill. What hapens on many is while your driving, combustion gases force the antifreez out into the overflow and it fills up and spills over.

You need to pressure test the cooling system. If it holds pressure, I would look at replacing the water temp. sensor. If it doesn't hold pressure, you have a coolant leak going on. If you don't see it dripping on the ground or inside the car, I would be suspecting head gasket problem.