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Old 01-31-2013, 09:35 AM   #1
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Join Date: Jan 2013
Location: Phoenix
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Water Pump Impeller Tips/Chips in your Cooling System

I pulled the water pump from a 2002 Boxster S. The composite impeller was missing the tip of 3 fins. I was able to locate 2 of the 3 missing pieces. I'm posting this summary of my experience for anyone that may find it helpful.

Re: Water Pump Impeller Chips


Originally Posted by Jake Raby
You dodged a bullet. Share this with all the people that bash us for being honest and say that such a procedure is a waste of time.
You must find the missing piece, but it may have come out in the coolant when it was drained?? If not, the most common place for it to end up is the bank 2 return just before the cross flow assembly.

Jake, thanks for the follow-up. I strained every ounce of coolant and flushed water that came out of the cooling system. Found many tiny pieces (about the size of ground pepper). But, not enough to account for the entire missing impeller tip. I'm guessing it is lodged somewhere as you've suggested.

(1) Would the "bank 2" return be the long coolant channel exiting the back of the heat exchanger?
(2) Is the cross flow assembly the area around the oil pump?
(3) Could the last piece be lodged in this oil pump area somewhere? Or is that pretty much an open channel back to the water pump? Short of pulling the engine and the heads, that would be the only coolant area I haven't disassembled.

If the last piece is lodged in one of the heads, I guess I'm going to be praying that it's not stuck in one of the thin walled capillaries. I've allways toyed with the idea of putting a larger displacement engine in this car. Looks like I may get the opportunity after all.

Thanks for sharing your valuable time.

I'm guessing the people that think this procedure is a waste of time find paying someone to do a major repair less painful than ... taking the time to minimize the risk of a frequently observed failure.

I'm not sure how to attach this to an existing thread. So, feel free to do so if you think it may help others.

To date, I would highlight these thoughts regarding this exercise (the hunt for plastic impeller tips in Boxster S cooling system):

Reference JFP posted diagram for direction of coolant path. Hot coolant from engine enters the radiator through the top radiator hose. Cooled coolant returns to engine from bottom radiator hose.

Water pump impeller blades

You may also want to view this next link for a more detailed understanding on how to REVERSE flush your cooling system.



(1) The HEAT EXCHANGER (oil cooler) is easy to access and remove. Given that I found 2 of 3 missing impeller tips just floating in this channel, I would say anyone with nominal machanical ability should invest the time to look here. I would also note that these tips where absolutely whole (fit perfectly back on the damaged water pump impeller) ... making me think that the probability of a tip breaking down into smaller fragments is unlikely.

(2) Getting to the radiators is a much more time consuming job. Based on the size of the coil pathways, I would expect that only very small fragments would be able to recirculate from here. However, once you see all the crap that gets stuck in the A/C and radiator fins, you'll be glad you have the opportunity to vaccume, hose, or power wash them clear. Aside from this added benefit, backflushing the radiators in place as a seperate system is probably sufficient.

(3) Removing the heater core also requires the removal of the windshield wiper mechanism. I would simply reverse flush it in place.

(4) Removing the coolant/filler tank was a pain. While the hoses to and from look large enough to carry a pencil eraser size impeller tip, the actual path through the plastic connectors is not that large. Visual inspection for impeller chips in the tank and a good shop-vac vaccume or back flush (includung the hoses) is as far as I would go here.

(5) Our Boxster S is a 6 speed manual. So, I can't speak to the ATF Cooler portion of the system.

NOTE: the composite impeller material does NOT float. So look carefully at the bottom of the bucket catching any flushed fluid and use a strainer to collect any foreign material to inspect.

In summary, I did not find the 3rd impeller chip in any of the above areas. Given Jake's experience ... it is likely stuck in a coolant capillary of a cylinder head.

Since the coolant flows to multiple chambers in parallel (not in a serial/linear path); I'm assuming that extensive back flushing of the block and heads could not effectively dislodge the missing piece ... back flushing pressure simply diverts to other capillaries without dislodging the wedged piece.

If this piece of water pump impeller is stuck in the location of a thin walled capillary; it is likely that the head will eventually experience the hot spot crack.

Perhaps (hopefully) there are certain locations where a trapped impeller tip does not lead to a warped or cracked head. Even then there is the possibility that the heating and cooling cycles of the running engine may be more effective at dislodging the piece than a simple cold back flush. So, it is still possible for the piece to recirculate (for better, OR WORSE) under normal operation.

In any case. As Jake has stated - "It's still in there somewhere."

Short of a design change or a risk mitigating workaround ... I really wish Porsche had added waterpump replacement as a regular maintenance item.

I didn't find this forum until I pulled the waterpump and saw missing pieces (never would have thought to change a waterpump before seeing a symptom of failure).

At this point I will probably install the lower temp thermostat HOPING to keep a potential hotspot below it's minimal point of failure. And then, look forward to a larger displacement conversion.

Jake thanks again for sharing your experience and observations!

Let me know if you think it makes sense to pull the cover around the oil pump (cross flow assembly?).

Thanks again ... mark

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coolant flush , coolant leak , cracked head , plastic impeller , water pump

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