Q: coolant overflow and overheating

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only when i drive distances over 5 mins away my coolant overflows and car overheats and steams but doesn't say on the dash that it is overheating.

My car has 125000 miles.
My car has an automatic transmission.

If your dash gauge showing engine temperature is working properly and the gauge shows normal temperature, a possible cause of the "overheating" you are describing is a faulty radiator pressure cap. The radiator cap is designed to maintain a closed system under presssure, and not allow overflow to the coolant reservoir, up to to a set pressure. If the cap is defective, coolant can boil due to the lower system pressure and, at the same time, hot coolant will overflow into the reservoir and possibly onto the ground depending on the volume of the reservoir. Of course, there are other possibilities such as a malfunctioning gauge and actual overheating. Initially, though, I would recommend that you request a radiator cap pressure test. If the cap is not the issue, the mechanic will then perform an engine overheating diagnostic. Either way, the responding certified mechanic will get this resolved for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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