2007 MX5, does not overheat and runs fine, cannot find a leak any wheres but every few weeks all the radiator fluid is on the ground.


Asked by glmelancon Aug 06, 2015 at 04:24 PM about the Mazda MX-5 Miata

Question type: Maintenance & Repair

2007 auto MX5 grand touring power top. Runs great, does not overheat .cannot find a leak in cooling system any where. every few weeks all the radiator fluid in the reservoir runs out, apparently thru the overflow hose. no indication of loss of fluid until this event happens. 105,000 miles.

7 Answers


Bad thermostat or a faulty pressure cap.


Could also be a head gasket leaking into the cooling system overpressuring the reservoir causing coolant loss.


how would you know the difference between the bad head gasket and a bad thermostat. I do not see any type of oily concatenation in the fluid. is it common for a thermostat to be bad on a 2007 with 104,000 miles. thanks so much for your help.

1 people found this helpful.

The coolant bottles on NC Miata’s often develop a crack directly below the cap. Look carefully at the neck of the bottle.

1 people found this helpful.

The (pressurized) reservoir on my 07 had a crack on the top of the neck right under where the radiator cap screws on. Easy fix and now, not leaking coolant.....but it still overheats; but only after driving highway speeds. It gets hotter when I am driving slow and stopping at intersections, etc.. Doesn't seem to be loosing coolant. I replaced the stat before I replaced the reservoir. Any ideas?

1 people found this helpful.

Pressure test the system you will find the leak. The problem is going to be your radiator. The tanks are pressed onto the core you will find the leak there.

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