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Hi AA
I have a 2009 Mazda 6 in a workshop with a overheated engine that needs replacing - again. This happened firstly in September 2017 last year and now again in March 2018. I purchased the car in November 2016. Apparently the thermostat failed the first time (which caused the engine to overheat) but they do not know what happened the second time. No failure mode is apparent for the second time (and now i wonder if it was for the first time either).
I was driving the first time the engine overheated, I remember that I could not get the heater to work.
The original replacement engine is outside it's 3 months warrantee period, however i am thinking that the replacement engine should be replaced (again) at no cost. They think that the only way to find the problem is to replace the engine and monitor it while running it - however that is basically what they did last time.
The garage have offered to replace the replacement engine for approx. 40% discount.
Do Mazda 6 cars have a habit of doing this?
Your advice on diagnosing the problem, or best course of action would be much appreciated. And should I really be expecting to pay out again?
thanks
Grant

Hi Grant,
There is usually a reason why a vehicle engine overheats and if caught early can minimise irreversible engine damage (seizing/ headgasket damage). Some engines are stronger than others and can handle being overheated to a certain point, however once and engine is overheated, it is generally compromised and it can often be a matter of time before damage eventuates.
As vehicles age, thermostats can stick, heater cores can block, cooling components can split/ leak ect. With a used engine, there is no knowing if this had ever happened and if the donor vehicle had ever overheated before.
So while the engine and cooling system worked when the car left the shop, it is the cheapest form of repair and a full system rebuild would have been the ultimate repair to put a guarantee on. However, as part of the used engine replacement, it would be expected that the complete cooling system would be checked/ flushed to ensure all possibilities of overheating have been minimised. Without knowing what conditions were made at time of repair, 6 months seems a reasonable amount of time to eliminate a vehicle fault as it would have overheated in a matter of hours/days. However the cause of overheating would need to be determined and maybe a tribunal could make the decision as to the longevity of this type of remedy under the CGA. https://www.consumerprotection.govt.nz/report-or-resolve-a-problem/general-problems/