It's quite funny that if you call up your local car factors, they will tell you they have an upgraded water pump with metal impellers .

Don't be a fool they are made out of plastics for a reason and not the one that the factors would have you believe that the main dealers are being cheapskate and are making the blades from plastic to save money.

I work as a mechanic and I've seen many situations over the years. Only recently I had a 2006 Astra with a broken water pump bearing. Fortunately for the owner it had a plastic impeller. Basically when the bearings colapsed the centre spindle sat quite violently off centre. As the impeller blades caught on the head they snapped off as they were designed to do. The timing belt hence did not snag and the valve timing was unaffected. Had the pump been made entirely of metal the story would have been very different and far more costly.

Remember one thing the pump blades are spinning freely in water and have no need to be made of anything but plastic.

Ok your going to argue that every now and again the plastic can break off for no reason. However this only involves changing the pump, rather than removing the head and changing valves of the metal one fails.

It's up to you guys working on your own cars !

I'm not going to argue at all, I've been saying the same thing for years!!

Let's hope that other people get the message.

Up to a couple of years ago, VW were offering quite good rates for their service exchange pumps (For service exchange, read brand new) I don't know if they are still doing this.

Regards

Yes mate they are very competitively priced only thing is there is an old unit surcharge. We always fit the real McCoy on VW's the max you'll save by going pattern is £10.

I was also under the impression that plastic impellors will shear if a careless owner forgets coolant and the block freezes rather than throwing the belt off. I have a plastic impellor on my AFH, still couldn't help but think "this is a bit shit" when I installed it though.

Your right they do look shit but I would definitely not fit anything else. You are correct in saying that if the engine coolant freezes it would also have the same effect (that is if you haven't cracked the block in the meantime)

I do wonder about using plastics in critical parts. They don't like heat cycling unlike alloy or iron. I see BMW use plastics in a lot of engine parts, like rad hoses and cam covers. Ticking bomb I would say.

Having had two plastic thermostat housings crack recently (one only lasted 320 miles!!) I would prefer a metal component over plastic any day!!

what I hate to see is plastic exhaust manifolds

The thermostat housings are very badly engineered I agree. Inlet manifolds are obviously made from plastic to save weight , be thankful you don't own a Daewoo where the inlet actually rot. On a BMW it is less harmful to have a metal water pump as they are never cambelt driven on any model in the last 20 years. The plastic water pump blades are however designed to fail safe where as metal won't

I get what your saying but at the end of the day I'd prefer anything on the engine to be made from a metal as it has a better temperature operating range & life and from the earliest engines, water pumps had metal impellors not plastic, it's being used as it's cheaper to produce and it will fail more often so keeping the supply chain in work/profit !!

Metal impeller for me too. If someone manages to let the water/coolant in the engine freeze and lock the waterpump then that is there own fault and problem if the impeller jams and chews the Cambelt. Other than that if the bearings fail in the pump then it doesn't matter what material impeller you have as both could lock up and chew the belt too

+1 Metal for everything else, except for the plastic impeller. Less corrosion build up inside the pump this way too.

I got a cylinder head from a 1.4 16v Arosa. The Arosa was scrapped because of engine damage caused by overheating (ally block, main caps can't be removed). It overheated because the plastic impeller had degraded and fractured in the middle, so it wasn't turning. A good car scrapped because the plastic impeller cracked.

Metal ones break ice. Ice breaks plastic ones.

Metal ones don't rust if you use a quality rust inhibitor coolant.

On other engine designs, metal ones may cause contact issues with a failed bearing. But not the short block VW lump, as it has a flange which sits in a recess in the block (both ally and steel blocks). In the event of bearing failure, the flange will bind and squeal, but the vanes cannot reach anything. The bearings would have to be completely collapsed, and then the cambelt wouldn't stay on anyway. The vanes are protected both sides (unlike say the Peugeot/Citroen design of pressed steel vanes unprotected, which act like a chainsaw until they snap off and have to be withdrawn from the block with a magnet!).

There is really very little argument for plastic on these Polo engines.

Well said Mikey :)