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Q: Coolant Leak

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Car has never overheated or had any cooling system problems until the other day. Suddenly it said "coolant low, stop engine". While it's sitting or idling, the coolant stays put unless the coolant reservoir tank cap is removed. I filled it up, tightly put on the cap and took it for a drive and suddenly all of the coolant was drained again. I would appreciate any advice on why it only drains while I'm driving and what it could be.

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

Hi there. The coolant can disappear for a number of reasons. The most common being an external leak. If it is not obvious as to where it is coming from then the system needs to be pressure tested. The water pump is a common place for it to leak without showing any leakage as the vehicle sits.

If there are no external leaks, then I typically do a block test, as a leaking head gasket can cause this; it will draw coolant into the combustion chamber and burn it off.

If you plan on having it repaired, consider using YourMechanic, as a certified mechanic can come to your home or office to diagnose your coolant leak.

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