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Hi,

I don't have any waterpump problems at the moment but I am considering changing my waterpump as a pre-emptive action (due to age more than km's).

My question is, how and why do water pumps 'fail'? I've heard of them leaking but what is the cause of the leak? is it just due to the age of gaskets? how noticable is a leak? I also assume there are other causes of failure which I would be interested to hear about.

Cheers

They are an impeller submerged in hot pressurised water dríven by a pulley of some sort which is external to the hot water and connected to the impeller by a shaft.
The shaft is supported in a bearing which wears, the consequent movement of the shaft then wears the seal which hold in all that pressurised hot water.

Of course the seal may just fail due to age, or the impeller wear usually because of cavitation.

Leakage of the gasket securing the pump to the block, if that were the case, are extremely rare in my experience.

The leak may just start as a small drip only noticed by a regular need to top up the reservoir, or a sudden and complete failure of the seal which will dump in essence, the entire contents of the cooling system onto the roadway, usually when in heavy traffic or just after stopping in some remote location after a spirited drive through the country.

In short, replacement at regular intervals is cheap insurance.

leakage is very noticeable in that you will get a pool of green blood on your garage floor.
Not too easily seen by peeking from the engine bay, but under the car, the bottom of your engine and gearbox will usually be very wet and dirty due to collected dust congealed.

If you are going to do a pre-emptive strike (great idea), change your belts, valve-cover gasket, CAS O-ring, and others at the same time. Buy a Gates belt and genuine Mazda OEM pump, seals, gaskets. They are things you touch only once in every 100,000km or so, and you want to do it only ONCE every 100,000km so it's not worth skimping $$ on.

I'd be happy to help.

Mazda recommends that the water pump be changed at 200,000 Km, however most people that do the work themselves change the pump when the timing belt is done at 100,000 Km. You remove/replace most of the same parts for the water pump as for the timing belt, so makes sense to do them both.