Which water pump? Plastic vs. Metal Impellers 

The name of the manufacture for the water pump you were trying to pronounce is Pierburg.

One problem with your theory, copper impeler not "metal" CAN'T eat engine block who is made of cast, forged iron or even forged aluminium..."Metal" impellers are the best!

I had a plastic one break apart. I use metal now

I’m steering more towards the Meyle WP, it comes with the composite impeller and 4 year warranty.

Metal elements (small pieces) migrate to small engine cooling channel jackets resulting in hot spots not good due to increased specific heat capacity of mild steel compared to plastic. The discussion should be about what type of bearing you want as there are different grades and race designs for improved reliability which will lower chances if plastic spinning on shaft etc. Porsche spec is plastic so stay with that as far as impeller is concerned.

If you change when your supposed to (often), I say an OE plastic pump. If the thing is going to sit a decade of occasional use, metal. Plastic is hard to predict in 10 years or tons of heat. Random plastic from anyone that is not OE is super suspect and equally randomizing the results. Every plastic vs metal impeller design I have seen was not a physical copy of the plastic form, but usually a simpler stamping or casting. I'm sure it hurts flow and makes turbulence, no one is likely to notice the effect but in the most extreme, and probably not even then. I have seen many broken plastic pumps, but all were super past the recommended replacement in orders of magnitude. In addition to all the plasticizer migrating out of the impeller, I think the resonance from a failing bearing has caused the final crack in the now brittle product and subsequent overheat. Usually a pump bearing off kilter enough to start making contact with the block is leaking enough the neglect has caused a failed head gasket from the perpetual low coolant situation. (and thus was quite noticeable via noise, puddles, or both before contact with block)

I changed m8ne to metal on Audi. TOTAL ENGINE FEALURE

Just replaced mine, car was overheating, I went with metal, it’s been a few weeks, this is no longer a daily driver so it will stay stored and used occasionally on weekends. Just did an oil change and did some driving it’s operating beautifully, levels maintaining no leaks or funky sounds Interesting there is slight condensation above the tank, I will be replacing the bleeder valve thinking that might be it…😅 any insight as to that?

That may work for porsches as your impeller is small, however Audi/Volkswagen's impellers are prone to disintegrating. Hence the metal.

Water will leak for weeks before impeller touches other metal. Problem with plastic impeller is that it starts to freewheel on the shaft thus not moving water.

I know loud radios and noisy exhaust systems, sell a lot of car parts! This is true. Ethylene glycol mix with water is coolant. So, if the circulation pump has a bearing failure, it starts of noisy long before total failure. After total bearing failure, if the impeller is cast iron or stamped steel, you would get even more noise. This would normally be heard, inspected and caught long before any block damage would happen. The reduction of weight is why more plastic shows up on parts or complete parts for performance, fuel economy plus emissions. Companies have to meet “CAFE” standards each year or pay a fine. The truth is, that companies SELL credits from one to the other. This occurs as the cost of fuel changes and buying habits follow. If fuel is expensive, then hybrids, electric or small vehicles sell better that more expensive SUV’s and Trucks. I have worked on vehicles since the late 60’s with no tech school, internet or RU-vid. I ask questions, watched but must have had some talent. There was a time when gas was $19.9 cents per gallon, drum brakes where normal on the front and your rebuilt water pumps. I might have a can of water-pump grease, even though it’s only job is to circulate coolant thru the block, heads, heater core and radiator, with the thermostat controlling the coolants temperature while under pressure. The pressure cap holds between 17 to 21 LBS., to raise the temperature of coolant way higher than ambient air. This makes the exchange of heat more efficient regardless of outside air temps or altitude. I won’t use a circulation pump sold with a plastic impeller are they too, can on handle so many heat cycles before failure. It’s chemical name is “PLASTIZIUM FRACTURITUS”. ASE Master Tech since 1978 - Retired

Did you mean Pierburg?

Metal and keep the coolant changed seems more practical. Plastic reaction to chemicals age and other worn engine stuff in the cooling system is beneficial to not have to deal with. So both types can wear out on bearings and impeller.

Thanks for the information. it help me lot to make my choice .

Well the pros and cons a plastic and metal drilich way in the engine block if it's aluminium plastic will Shatter causing the engine to overheat you might be able to change the housing or repair it a lot cheaper than an engine

Great topic I was wondering about this myself.

My '98 Ford Taurus plastic impeller was in 3 parts. New ones might be made with improved composition.

Will you not hear the impeller grinding metal long before it destroys something? The metal impeller on most aftermarket pumps is some kind of cast aluminum alloy = quite soft!

I was planning to use a URO water pump for my 996. What are your thoughts.

plastic is not plastic and there are also variants in metal. Long time ago the vendors tried to save cost with cheap plastic, but if PP GF40 is used, it should last a long time. Plastic has better flow and lower load on the bearing which fail often on water pumps. On metal it can also fail on the weld, cast iron has also a limited lifetime. Some vendors use brass, not sure whats the advantage. Its quite soft and corrossion shouldnt be a big problem. So every material has its pro and cons. Just saying metal vs. plastic doesnt tell anything.

Hi.. Any one explain.. How can I increase the flow rate in waterpump... Now currently have cast iron impeller.. If I go to plastic impeller.. Flow rate can increase???