I own a 2003 Honda Civic Ex. Of course 100 miles past 100,000 miles, which is when the warranty expired, the car begins to overheat. In the years I have had this car the temp gauge NEVER moved. When it almost hit red I pulled over and saw coolant had spilled out of the reserve tank. The car wasn't smoking at all and s the car cooled the reserve tank slowly emptied. The fans looked fine so I replaced the thermostat and radiator hoses. In the process I noticed no mineral build up and everything looked clean. The car still overheats but not as hot. It is only after about an hour of driving when I head up the last hill before home. I just ordered a new coolant temp sensor and thought I would try that but that is just a shot in the dark. Any one have any advice?

This link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post235973

That website was really informative and I appreciate the help. We decided to go with replacing the radiator once we learned they are prone to go bad in Hondas at 100000. The car drove fine but as soon as we had to drive it up a big hill during the middle of the day the reserve tank filled and overflowed and the temp gauge raced to red... we are stumped and are thinking about giving in and taking it to a mechanic... any alternatives?

Did you refill the system properly, ensuring there is no air in the system?

The thermostat may be sticking. Test the thermostat in a pan of water with a thermometer--even new ones can be bad. Best to go OEM. Also, ensure you can feel adequate coolant pressure from the water pump. Outside of replacing the water pump, you should be able to solve the problem yourself.

Ok so I am a girl so I can admit this car has me in tears. We took it to a shop for 3 days they tested the head gasget and thermostat and everything else and drove the crap out of it and nothing. It drove perfect. They sent us home saying our car was perfect and an hour down the road it overheated again... it seems to be a time driven thing... im so lost..

If the overflow tank empties slowly, when the engine cools down, the radiator cap may be bad. By increasing pressure, radiator caps allow the coolant temperature to be about 30 degrees higher than it would otherwise. Additionally, they have two valves in them. One allows the hot coolant to flow into the overflow tank. The other opens and allows the coolant to flow back into the engine, when it cools down. Go with an OEM replacement, if you suspect this could be the problem.

Does the radiator cooling fan work properly?

Many Hondas overheat, due to incorrect installation of the thermostat. Make sure you used a genuine Honda thermostat with the proper temperature rating.

Ensure the brakes, including emergency brake, are not dragging. Ensure you are using only the NGK spark plugs that originally came in the car. Check the timing.

For a test, completely remove the thermostat and see if that solves the overheating problem.

KEEP ME POSTED.

The only thing that the mechanic did the first time the car went in was change the cap so it was new when it last overheated. They took the car back and are planning on doing some test with by dyeing the coolant... they also plan to replace the thermostat with an OEM thermostat. The fans seem to work fine but we don't know if they are shorting out and causing the car to overheat and then kicking on too late. I have owned the car since it was at 30,000 miles and the only thing I have ever replaced was the catalytic converter so I think it still has the original spark plugs. For now we are at the mercy of the mechanics and all their tests.

You definitely want to change the spark plugs with the identical NGK plugs that originally came in the car. It's best to replace platinum plugs every 45,000 miles or 3 years, whichever comes first.

Hopefully, the dye test will turn out negative.

Once you solve the overheating problem, start using full-synthetic engine oil; e.g. Mobil 1 or Pennzoil Platinum. This will help the engine to run cooler, last longer, and perform better. Change synthetics every 6,000 miles or 6 months, whichever comes first.

The dye showed them that the coolant was leaking into the 3rd cylinder head. So they are back to wanting to replace the head gasket. And since they are going to be in there they want to do the water pump and timing belt just for maintenance. Hopefully that will be the end of it. Thank you for the advice on the oil!

Sounds like an excellent plan. Have them refill the cooling system with a 50/50 mixture of Dex-Cool antifreeze and distilled water--otherwise, buy prediluted. Change it at least every 3 years. This link should help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-7.html#post1365453

Head gasket problems can develop from using the wrong antifreeze. Don't go along with the "universal" antifreezes on the market today. Only use what Honda recommends for your year Civic.

If you follow the preventive maintenance items below, your Civic should last 300,000 miles:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563.html#post219991

Be sure not to overlook regularly changing the transmission fluid.

You may want to also have the mechanic replace the timing belt tensioner.