Water pump

[colcol]

Has anyone had any experience with water pumps with plastic impellers breaking on the 932 cars?, i read on some forums to only use pumps with metal blades, but when i tried to buy one in Australia, no one had one, they told me that they had never had a problem with the plastic ones, but that could be just trying to sell me one, i settled on a Quality well known brand, and when i pulled the old pump one out it was a Genuine Alfa Romeo pump and guess what, it had a plastic impeller as well, the problems i can see with a plastic impeller is that the plastic may get brittle and shatter, the advantages i can see is that it wouldn't corrode and end up full of 'barnicles' and reduce the ability to pump the water, but if you do the right thing and change the water pump every 2nd cam belt change, that is every 6 years or 100,000kays i am hoping it will be ok, a water pump failure would mean a cam belt failure which would mean a engine rebuild, as a leaking water pump would leak coolant onto the cam belt or the water pump bearing would seize up and lock solid causing cam belt failure, as the water pump pulley also acts as a tensioner of the cam belt, any experience with this subject?, Colin.

[Jekyll and Hyde]

The plastic impeller water pump issue is only common with the V6s.  Don't know why it has become common opinion that 4 cylinders have the same problem.

On the V6 water pump, the metal shaft that goes into the centre of the plastic impeller expands with heat more than the plastic.  Over time, this causes splits to form in the plastic impeller, originating at the metal shaft in the centre and working their way out.  When these splits get bad enough, the impeller can actually spin on the metal shaft it is supposed to be attached to.  Which means, although the pulley and shaft are spinning away happily, the impeller which actually pumps the water is stationery.  Usual symptom of this condition is overheating in freeway conditions, but normal temperatures around town.  It appears that 3,000rpm means the water provides enough resistance to get the impeller slipping, but lower rpms the impeller still spins as intended.

4 cylinders use a quite different pump, different size and shape impeller, and different sized metal shaft, and don't seem to be prone to the same behaviour.  Not to say it isn't possible, but pretty unlikely, as compared to a V6 wherein every plastic impellered pump that comes off at 60,000km has big splits developing.  Which is probably why you couldn't buy a 4 cylinder one with a metal impeller, I don't remember ever seeing one...

[Steve S]

For the record I have seen a 164 twin spark with the plastic impeller loose on the shaft. I was of the opinion the twin sparks were just as bad. 

[John Hanslow]

I know that with 932 series cars it is a V6 issue and when purchasing, you check that with the first belt change the pump was upgraded.

Barry Williams (2003 V6 Spider) queried the mechanic who did the belt and pump .  The workshop was not sure but bought the parts from The Italian Job in Clayton.

A call to them confirmed that they only stock the upgraded pumps with metal impellers to overcome this particular issue.

Cheers