The water in my radiator keeps depleting I've checked for leaks but I can't seem to find any. Every morning when I check the radiator I have to fill it up for about a litre. Yesterday I didn't use the car much so I topped the radiator water at night to see if it stays the same in the morning. And no, it didn't. I still had to top it up half a litre of water even though the car was idle the entire night. I still couldn't see any leak. What could be the problem?

I drive a 2001 Honda Civic.

2 Answers 2


You want to make sure you do not put tap water into the cooling system on your vehicle. The cooling system has a leak, which is why you need to refill it periodically.

Look on the ground where you park and note any wet spots. Check all the hoses to and from your radiator for any signs of a leak such as wet fluid or runny looking patches of evaporated fluid (can have many appearances). Check around the radiator itself, and around the reservoir. Look for steam or "white smoke" from the engine bay and exhaust pipe while the car is warm (not when you first start it!!!!) and running. If you don't see any at idle have a buddy pull on the throttle. You can pull the spark plugs out and make sure they all look the same.

If nothing else, you can buy a tool and pressure test the cooling system. Sometimes the system will hold at idle but not on the road. Beyond that it may be time to take your vehicle to a mechanic for diagnosis. Good luck!

  • I've been told before not to put tap water. Can I ask what difference it makes? I did check for leaks but I can't seem to find any. And yes, there is steam coming out of the engine bay when the car gets heated which eventually stalls the car and I have to let it cool down and refill about three litres of water for it to start working again. I think you are right about taking her to a mechanic for diagnosis. Thanks!
    – Lazy Hazy
    Commented Apr 20, 2016 at 7:15
  • 1
    The difference is that tap water will cause corrosion inside your engine - proper coolant has corrosion inhibitors to prevent this. Plus if you live in a cold place, tap water will freeze, expand, and destroy your engine...
    – Nick C
    Commented Apr 20, 2016 at 9:29
  • 1
    @LazyHazy When it starts to steam, pop the hood and see where the steam is coming from. Likely a pinhole leak in a hose or the radiator that doesn't leak until the coolant is hot and under pressure.
    – rpmerf
    Commented Apr 20, 2016 at 13:26

You also need to check the coolant tank if it has one, it may have a leak or the connecting hose has a leak, and when the water in the radiator expands, it's lost to the leak.

  • I'll check that one out.
    – Lazy Hazy
    Commented Apr 20, 2016 at 10:24

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