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2000 Honda Civic LX 250,000 miles on it. Well maintained car, I have owned it for the past six years and bought it from the original owner. Every so many months, I have to add fluid to the over flow bottle. Radiator is always full when I do. The oil looks clean the radiator fluid looks clean. Car has only ever overheated a few years ago because of a bad radiator. I want to take this car on a long trip next month. Should I be concerned about the head gasket? I will more than likely take it to get a leak test but I am just curious what your thoughts are.

 
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How many months? How much driving do you do in a month? How much fluid? Do you live in a hot climate?
no evidence of external leaks?
You'd probably be fine as long as you kept your eye on the level.

 
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Around 700 miles every three months fill overflow to fill line not hot at all. The trip I want to take will be 2700 miles round trip and it will be in the heat 100 plus degrees on some days. I plan on replacing the thermostat, the radiator with a 2 core aluminum and a better fan

 
Rep Power: 223

If you're just filling the bottle every 3 months you should be fine, especially if you keep an eye on it. Typically when these cars have a head gasket failure they push coolant into the bottle