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I have a 2008 Mazda 3. Since I got it (about 2 years ago) it is loosing coolant fluid constantly (and it is getting worst: now I fill in a liter of fluid a day). The mechanics in the garage can't find a leak, but they replaces the container, the thermostat, and more. Lately, I noticed that the leak happens when I start my car. Not while driving or Idling, only while starting. Any Idea what could cause such a thing?

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To identify the cause of a coolant leak, there are 2 general options:

  • clean the crap out of your engine bay, make it squeaky clean so that you can SEE where fluid is leaking from
  • add an ultraviolet dye to your coolant, and after running the engine (or starting it, in your case), go over the engine bay with a black light

Common causes for coolant leaks are:

  • worn out water pump or water pump gasket (look at the pump while the engine is starting or running, inspect your belts for coolant while the engine is off)
  • loose hoses (personally, I replace the snap rings that come from the factory with screw-tight hose clamps, the kind you would use to fix your garden hose, picture below)
  • cracked radiator (look at it from all sides, look for stains)
  • some engines have coolant passages in the timing cover, if the rubber o-rings rot, you will have a leak in there. On most engines, this is a lot of work (a lot of disassembly). Depending on the specific engine design, the coolant may leak into your motor oil or leak out of the edges of the timing cover.

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There's only 2 places missing coolant can go:

  • outside (you would have found a puddle, or at least some stain marks)
  • inside the engine (burning coolant turns your exhaust white)
  • Right.. the fluid goes outside, but only when starting the engine. what do you think is the cause? – Oded Busharian Jul 3 '17 at 8:37

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