Cam Belt Age . . .

Cam belts often show signs of wear - cracking etc - but this isn't always a sign of impending doom, as it can happen quite soon after fitting. The only certain way is to follow the maker's service intervals. Which of course you may not know if they have been followed with a used car.

Whether to change things like the water pump and tensioner as a matter of course would depend on model. If they are easily changed later, not sure I'd bother. Just why some water pumps fail so easily while other belt driven units like the alternator, steering pump and AC compressor don't, I've never worked out.

Perhaps because the water pump is the only one trying to keep a corrosive liquid separate from the bearings?

Chris

Now *that's* my kind of photo album... ;-)

Eh? Seals on an AC compressor are a failure point. The reason why they don't last anything like as long as a domestic fridge.

And many high powered alternators are water cooled.

And I'm not quite sure why you'd use a corrosive liquid in an engine mostly made of various types of metal?

Most cars are watercooled...

Yes, but they are lubricated by the oil in the refrigerant, and rarely run for the same number of hours as the engine.

Many? A few are, but the coolant only passes through the stationary part of the alternator, so there are no seals on rotating parts.

Coolant is water with additives. It will still corrode mild steel when in contact with the air. (And of course many engines are used without adequate additives present.)

In the days when it was worth trying to repair things, I've dismantled water pumps in order to replace the bearings, but once apart it was clear to see the futility of attempting to do so because the rubbed area of the shaft was too badly pitted.

It's common to see in an engine that has not been run for some years. Shortly after getting it going, the water pump will start to leak because the shaft corrosion tears the seal, soon to be followed by the bearings failing.

Chris

Indeed. With an additive specifically designed to inhibit corrosion. Oh - water isn't corrosive anyway.

Then use something more durable than mild steel? Given the vast cost of possible engine damage if a pump fails?

Fact remains is some designs eat water pumps far more quickly then others.

IANAC (I Am Not A Chemist) so delete 'corrosive' and substitute your preferred term for what happens when commonly used metals containing iron mix with water.

Chris

But that is not what was being discussed; I was suggesting a *possible* reason why *in general terms* water pumps fail more often than other items that are usually driven by the auxiliary belt.

I stand by what I said.

Chris

IIRC, it's the presence of oxygen and water that cause rust. But then many engines are ally those days. And I doubt you *must* use steel in any part of a water pump.

I'm certainly aware of what often fails in a water pump. But am merely questioning why. After all, domestic heating systems can pump round water at about the same temperature for many many years without the pump failing.

And a domestic pump - surely at least as complicated as a car one - costs similar money, or in many cases less.

Central heating pumps have no shaft seal. The rotating part is in its own chamber and is magnetically coupled. That's why, on old systems that only used the pump for heating circulation, there would be a lot of failures at the first use in the winter. The chamber would just need cleaning out to fix it, and some pumps have a cover over a screwdriver slot that you can turn to get the pump started again.

Modern systems have a 'pump-saver' mode where if the pump hasn't run for 'x' days, it gets switched on for a while - one of the reasons why you should always leave the boiler with an electrical supply.

Chris

It was the use of mixed metals that mandated year-round coolant. Old, basic anti-freeze was intended to be drained out in the spring as it lowered the boiling point.

Of course, it would be entirely possible to make every part of a car virtually fault free, but where's the money in that. ;-)

Chris

Most domestic water pumps don't have sealed drive shafts, they have magnetically coupled impellers.

Primarily because the power source is AC mains, so getting a rotating magnetic field is easy.

Could be done on a car, of course, but there may be cheaper ways to make a mechanically-coupled pump more reliable.

mumble, mumble, thermo-syphon was good enough in the old days, mumble, mumble

mumble, mumble, so were side valves, mumble, mumble :-)

and side valve engines are still being made for light aircraft, light weight, reliable, simple.