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Q: Resevoir Tank Over Full

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The Resevoir pulled coolant from radiator and overfilled. Temp. Gauge is slightly higher than normal, it's half way now. Is the radiator bad or going bad?

My car has 122297 miles.
My car has an automatic transmission.

The coolant can be over filling the reservoir for a couple of reasons. Always start with the simplest options first. One of which will be a failed thermostat. You can bench test this by submerging the unit in hot and cold water and check for proper opening, but it may be easier to just replace it. Secondly the amount of coolant in the system can cause the reservoir to overfil. This would only happen until the levels came down to normal range. Another issue may be the use of multiple types of coolant in the system. You may want to flush the radiator and put in one kind of coolant (50/50 mix only). If the coolant is overheating to the point the fluid is expanding and causing the issue, you will want to make sure the fans are assisting the radiator as they should be. The very worst option would be a failed head gasket. They would likely cause a number of other issues with the drivabilty of the vehcile.

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