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Old 06-30-2011, 02:34 PM   #1
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Water pump impeller blades

Seems to be a rash of water pump failures these days...

OK, got the failed pump removed (along with the engine mount, for replacement) and was hoping the impeller blades would be intact. They were...sort of:





The obvious question (with, it seems, not so obvious answers) is: How many people would worry about the small amount of the blades that's missing? I don't yet have the replacement (it's ordered), so I can't tell exactly how much is missing. Is it big enough to meet Jake's "pencil eraser" cut-off? Dunno.

How many people (especially those with specific experience in this area) would
1) disassemble the entire cooling system looking for pieces
2) figure out some way to back flush the system
3) not worry about it, and slap the new one on
Jake, I suspect you'll hit me with your well-noted 'doom and gloom' response (no offense!), but level with me here...As a former Marine, you're obviously something of a gambling man...how much of a gamble we lookin' at here, going with Option 3?

If the consensus is to do Option 1 or 2, is this something a novice mechanic (but getting more experienced all the time ) working in a garage, with jack stands and a decent set of tools could hope to pull off?

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Old 06-30-2011, 03:26 PM   #2
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Hi Doug - looks like your preventative maintenance is keeping you busy.
As to the damaged impeller, does the damage look like an actual breakage or erosion of the plastic - difficult to see from here. How many miles /years has the pump done? I bet you were losing 25% of your coolant flow looking at the impeller vanes......

If its erosion, there shouldn't be a problem, but if bits have actually snapped off, then the debris could still be in the system. The first place I would look ('cos its easy) is in the thermostat housing to see if the thermostat has stopped the damaged bits from circulating. I think Jeff (JFP in PA) has suggested in the past to "back flush" the system to make sure any loose bits are flushed out before bolting back together - how difficult this is I'm not sure but its probably easier and cheaper than having a coolant blockage in the cylinder heads.

I'm sure one of the professionals with more experience than me will chime in with some good advice...
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Old 06-30-2011, 03:29 PM   #3
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Try doing a reverse flush and see if any of the pieces come floating out. The thermostat will have to come out and then use (if possible) a flush nozzle. Good chance is you'll recover your missing plastic.
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Old 06-30-2011, 04:12 PM   #4
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FWIF when I replaced mine a couple of weekends ago, my faile pump looked similar to yours, maybe just a little bit less impeller damage. Mine started to leak and then I got some slight chirping noise before i shut it down after about a 2 mile drive home.

I didn't even take a close look at the impeller until after I got the new one back in. No bits in the old coolant and I didn't back flush.

If I had to do it again, I would back flush, espacially the the engine a couple of times. But I don't know what the procedure is.
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Old 06-30-2011, 06:52 PM   #5
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Quote:
Originally Posted by Steve Tinker
Hi Doug - looks like your preventative maintenance is keeping you busy.
As to the damaged impeller, does the damage look like an actual breakage or erosion of the plastic - difficult to see from here. How many miles /years has the pump done? I bet you were losing 25% of your coolant flow looking at the impeller vanes......

If its erosion, there shouldn't be a problem, but if bits have actually snapped off, then the debris could still be in the system. The first place I would look ('cos its easy) is in the thermostat housing to see if the thermostat has stopped the damaged bits from circulating. I think Jeff (JFP in PA) has suggested in the past to "back flush" the system to make sure any loose bits are flushed out before bolting back together - how difficult this is I'm not sure but its probably easier and cheaper than having a coolant blockage in the cylinder heads.

I'm sure one of the professionals with more experience than me will chime in with some good advice...
As to your question, How would you distinguish between "actual breakage or erosion"? The exposed edges (where the small amount of plastic has disappeared) are roughened---don't know if that tells us anything. The optimist in me says that erosion would do that, that if the pieces suddenly were snapped of they'd leave an irregular but smooth edge. Does that make sense?

I did take off the thermostat, and saw no parts in or around it, or the pump.

I'm not really sure about how to go about back-flushing the system. If anybody knows of (or wants to create---your good deed for the week!) a DIY, I'd be all ears.

I assume it's the original pump. I'm the second owner. Car has 57K miles; got it in 2005 with 19K miles.
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Old 07-03-2011, 07:58 AM   #6
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quick cooling system primer:

water is ALWAYS circulating through the engine, regardless of whether the thermostat is open. to properly flush the block, remove the water pump and force fluid into the CENTER hole behind the water pump. this reverse flow fluid through the block first, then the heads, & then back out through the OUTER two holes behind the water pump.

when the thermostat does open, flow is FROM the block TO the radiators THROUGH the thermostat (true on all cars). water returns from the radiators to the engine & enters the engine on the left hand side of the car through the oil pump housing.
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Old 07-03-2011, 12:05 PM   #7
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OK, sorry to be so dense, but I need to get specific here...

To begin with, I currently have both the water pump and the thermostat off the car. This is what it looks like:




I've labeled the openings into the chamber where the thermostat lives.
A: The big opening over which the thermostat housing is bolted, with its gasket. One of the big hoses (either going to or returning from the radiators) attaches to it.

B: Follow the arrow; this opening goes up to the center opening of the water pump (where the impeller blades reside).

C: This is the opening over which the bottom part of the water pump unit attaches; it's got a small hose coming off it that I believe goes to the heater core and the bleeder valve.

D: This is the opening seen at the back of Opening C. It travels off to the right somewhere, I think communicating with the other big hose that makes up the circuit through the radiators. Don't know if it goes anywhere else.
As far as I can figure, the thermostat opening and closing affects only one thing: movement through the big opening A. Movement through B, C and D are not affected by the thermostat, right?

OK, to your suggestion specifically, ie to send water through the center hole of the water pump. So you're talking about fitting a hose (somehow--I have gotten some suggestions) onto Opening 1 here?:



I'm assuming you mean do this with the thermostat on, otherwise water simply runs down through B all over my garage floor. (As far as I can tell, Opening 1 goes only that one direction...wish I had one of the flexible endoscope videos!) So, if I put my t'stat on, do I do it with the t'stat itself in the housing? Being cold, it would be closed and prevent water movement out through the big opening A. [[ And since the water pump won't be turning, I guess little/no water will be going up through B. IGNORE that previous sentence---I wasn't thinking when I wrote it: the water pump isn't installed at all while we're flushing ]] So that leaves Cand D. Is that where we want water to flow, in order to flush out the block and the heads?

Last edited by Frodo; 07-03-2011 at 06:25 PM.
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Old 07-03-2011, 02:04 PM   #8
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you want the water to go in through 1. to make this work, you will want the thermostat housing on the engine WITH the thermostat installed. you will also need to plug C/D. it would also be best if you clamp the big hose on the other side of the engine as well (goes to the radiators).

the idea is to isolate the engine itself from the radiators & heater bypasses. when you get it right, water forced into 1 will come out of 2/3 after having fully circulated through the block and heads. FYI you will need a VERY good seal, as the engine really holds a lot of water. not even sure a common garden hose will supply enough volume/pressure to shake any sediment loose.

if you have trouble sealing off a hose into 1, i think as a (slightly less effective) alternative, you could re-install the water pump & unclamp/remove the big hose from the other side of the engine. attatch a hose to the water pump (pumping into C/D in your diagram) & pump the water out the other side of the motor. you will miss some passages this way.......
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Old 07-03-2011, 05:50 PM   #9
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Nice thread...and great pictures keep it up
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Old 07-03-2011, 06:04 PM   #10
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OK, Insite, I'm still confused...Suppose I'm a cockroach crawling around inside that chamber we're talkin about, all warm and fuzzy about my choice of hangouts---after all, I'm kind of hidden but I've got escape routes through A, B, C and/or D. Now---you said I should bolt on the thermostat housing with the t'stat included, AND also block off both C & D. With the thermostat cold (ie closed), I, the cockroach, am not going to be able to crawl out through A, and additionally C/D have also both been blocked. That leaves B as the only way out, and that's where you want me to put the hose (actually 1, but that goes only one place: down through B). Once that's done, and the water turned on, there's no escape for either me or the water---it's a locked box with no exits. What am I missing?
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Old 07-04-2011, 07:53 AM   #11
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frodo -

you can't see it in your photos, but there is an 'E'.......

hang on; i'll go take a photo of one.
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Old 07-04-2011, 08:00 AM   #12
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re-reading your post, you had it labeled as D.

basically, when the thermostat is closed, water gets sucked from C & D into the wather pump inlet (1). it is then forced through 2/3 into the heads, then the block, then back through D. you want to reverse this by flowing water into D.
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Old 07-04-2011, 08:22 AM   #13
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You da man, Kev.

How'd you get that photo???
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Old 07-04-2011, 08:45 AM   #14
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Old 07-04-2011, 10:45 AM   #15
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you know, i'm looking at these pictures now & something concerns me. when i spoke earlier about coolant flow bing from the engine to the radiator over the thermostat, it was a general comment; cars are engineered that way for a reason. FYI, a centrifugal pump like the boxster's water pump is designed to suck from the center and blow to the edge, so we can deduce direction this way.

looking at our photos, two things strike me as very odd:

1. the thermostat opens to the low pressure side of the water pump. this means that the pump IS sucking water from radiators across the thermostat. this is not common, and strikes me as incredibly stupid. the cooler water from the radiators would cause the thermostat to start to close again almost immediately. the temp the thermostat is 'seeing' is the cooler radiator water combined with some engine recirculated water. this would imply our 190deg thermostat is actually running the engine at MUCH higher temperatures.....by design. essentially, the thermostat would try to achieve a 190deg exit temp from the radiators. hmm.....

2. the second thing is that our thermostat looks like it may be two thermostats in one. it looks like the bottom of the thermostat covers 'D' in the photo & like a second spring/actuator rod opens this second 'stopper'. my GUESS is that this is an attempt to heat up the heater core / passenger cabin before any other concern. i want to drop one into a water bath to see if this is the case.....

raby's point w/ the low temp thermostat is that when they measure engine temp at multiple points on test motors, they see some areas that get really hot WAY before the OEM thermostat starts to open. this design could be a reason why.

anyone else have thoughts on this?
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Old 07-04-2011, 11:07 AM   #16
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Old 07-04-2011, 11:12 AM   #17
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insite,
I think we are missing something here. I need to look at a complete cooling system diagram to get clear on this. I can hardly believe Porsche set it up so coolant water flows from rads to t-stat to motor. It makes no sense.
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Old 07-04-2011, 01:31 PM   #18
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JFP - good diagram; pretty much sums it up.

Topless - I poked around my spare motor today; the water pump DEFINITELY pulls water past the thermostat. The TStat is downstream from the radiator. Seems a bit of a mistake to me.
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Old 07-04-2011, 01:36 PM   #19
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Checked a vette lt1 diagram and it's the same; thermostat downstream of radiator. WTF? Makes no sense to me. What am I missing?
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Old 07-04-2011, 02:17 PM   #20
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Btw frodo, this doesnt change the direction you want to flush the motor at the pump

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