Q: my car leaks coolant but is fine with water. it also recently had a new water pump and thermostat put in why would this happen?

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when i bought my car they said they had just replaced the thermostat and water pump. It overheated the same weak and all my coolant leaked out. I put water in it then i had it flushed and refilled with dex cool and now everytime i put coolant in it it leaks but when its only water it holds better and leaks less. Why would this happen?

My car has 140000 miles.
My car has an automatic transmission.

You are probably just seeing "randomness" in the leak rate when you add water versus coolant; both will leak at the same rate. What you want to do, of course, is just simply get the leak pinpointed and repaired. If the cooling system leaks, it obviously will not hold maximum pressure either and the coolant will then potentially boil over and that itself creates overheating (pressure in the sealed cooling system RAISES the boiling point of the coolant). Engine coolant can leak externally through a hose, radiator, water pump, etc. or internally due to a leaking head gasket and sometimes a leaking intake manifold gasket depending on the engine design. External leaks are typically found by simple pressure testing of the cooling system. To find the leak that exists in your case, and get the required repair estimated, please request an engine cooling system leak diagnostic and the responding certified mechanic will get this resolved for you. 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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