BC

I'll take one of those early ones. Actually 2.

If you still have them.

GregBBRD

Only ever seen this with rebuilt pumps....not pretty.

GregBBRD

How about one? I had a couple people call, instead of posting.

hlee96

I'll take it! Will Mary send me info via email? She says she will contact me if there was any left.

Thank you-Hoi

antlee928

Hi, A bit perplexed about various commentary here and in various other posts at different times during my subscription to RL and that is the various discussions on metal vs plastic impellors and the metal impellors causing engine block damage. Now here in Oz a well know and very experienced Porsche factory trained engineer who runs his own Porsche service shop and services many 928s (most MYs) on a regular basis and is also factory trained on the 928s recently commented as follows on his fascination at the Here is an extract of his commentary,

"Water pump , now this is something that has fascinated me for some years now , I / we have been replacing water pumps on the 928 series continually since I first started working on 928 series in 1979 , thats now 37 years & I have never every in the decades & hundreds , probably thousands of 928 water pumps replaced have I every seen one water pump impeller go in towards the engine case , every water pump , meaning thousands in the last 37 years have worn outwards , meaning the impeller wears into the pump itself , away from the engine case
So aft er all these decades , reading the goings on on Rennlist about water pump impellers machining themselves into the crankcase , I have just read this in total amazement , as we do not see this at all , its the complete opposite

There is only two possible explanations I can think of of what has been seen in the States }

A ) there may have been some really poor rebuilt pumps years ago that "may" have done this , but I still can not see how it goes in that ( in ) direction , because the mechanical / leverage tension on the pump pulley , driven by the belt is always under high tension & its constant tension is in the up position & out ( NOT in ) , this explains why we only ever see water pump wear where the pulley & its shaft is migrating outwards & in doing so the rear of the impeller ( which is totally flat ) just wears slowly into the water pump housing , this is all we ever see & its quite no rmal for the very high tension the water pump is under

B) I have often wondered if some people who have removed a 928 water pump for the first time will see on the engine case the concave shaped area that the water pump impeller will go into & the human will see these quite strange looking marks & it quite frankly looks unfinished , but that how Porsche machined this area & its does look as if something , like the impeller has been biting into it , but its just the way this area was finished off & no two are exactly the same , they are all a little bit different , the hall mark of a hand built Porsche engine

Thank about it for one minute , in the early days 1978 to around about 1991 all the factory water pumps had cast metal water pump impellers & the teeth were quite sharp , if one of these made even the slightest contact with the alloy case the impeller would just take one bite & that would be that it would instantly seize as it digs into the soft alloy , particularly as the pump is being driven by the back of the belt ( smooth ) & this smooth surface is driving the smooth surface pulley , this would instantly slip , so there is no way it could just keep biting into the alloy case with those sharp impeller teeth

Around 1991/ 1992 etc the factory water pumps were made a but cheaper & one of the cheaper things on it was the much cheaper plastic impeller & yes with a few years of heat cycles these plastic impellers just came off ( plastic heat fatigue ) , same goes for the 944 ( same issue ), but they would normally get to the cam belt interval ( just ) & we are still living it with plastic water pump impellers coming off the 996 986 997 engines ( 911 / Boxter etc ) but with these its more of an issue because these plastic impellers break up into bits & the bits go into the cooling passages within the eng ine & heads & get stuck there & I mean stuck & I mean they do not come out at all

So I am not a big fan of plastic , but when the situation comes and there is no choice then SO be it

But with the 928 there is a choice & thats the Geba pump & its made in Germany , these have only been around for a few years( 4 or 5 I think ) but they have had no issues at all , excellent quality control , where as we used to get all sorts of issues with the other aftermarket brand , dribbling coolant from the breather hole & the odd failure , but with the Geba its been very good & it has the metal impeller which I like , but if Geba switched to a cheaper plastic one in the future , thats fine as well , I just have a slight preference for the metal one "

I would be curious to know Greg's, Rogers's and Sean's further views on this matter as I will have a water pump and timing belt replacement coming up and will need to make some decisions around water pumps including the tensioner - PKT vs factory std.

Cheers

Tony S4 MY89

ROG100

Tony,
Without going into pages of answers the crux is ----
Most major failures, but not all, were associated with rebuilt pumps.
Failures associated with good pumps, - Laso & Porsche - and in recent years, have been restricted to leaks only. Water from the front weep hole tells you pretty quickly what is going on long before it is an issue. Failure rates om modern Laso pumps (last 4 years) are less than 0.25%.
Remember that Laso sales outnumber Porsche by 20x at least.
GEBA is a new unproven - in the long term - water pump with a METAL impeller which is considered by most to NOT be the best choice. Been on sale for about two years and so far so good.
I hear what Bruce has to say and hold his opinion in the highest regards as I do GB, Sean and others.
IIRC Porsche changed to the plastic impeller because of issues with the metal impeller not staying on the shaft and not cost cutting. However I was not in the 928 business in the 90's so will defer to others.
If you are not using a PKT and you have an 87+ car you have three choices all of which are good and seem to have no (catastrophic) issues ---
Modified Laso - early
Porsche
GEBA
I did not include the Guardian as to me it is highly modified (I do not mean in a bad way) and not a standard choice for most users.

Imo000

Anyone has hard evidence that Porsche changed the impeller to plastic because of block damage? Or is this just internet folklore?

ROG100

Well when Laso changed to the plastic impeller it cost them a lot of money and increased the price. All cheap 928 water pumps have a metal impeller. If plastic was a cheaper option they would all have plastic you would think.
Really does not matter either way as currently there are no failures with the impellers on the current preferred pumps.

bureau13

They haven't seen this in Australia because it's in the Southern Hemisphere, duh. Everyone knows water pumps turn the other way down there.

(Hey, somebody had to say it..)

SeanR

I've had 3 pumps that I replaced that were pulling outward. I had saved one of them as a trophy until a couple weeks ago when I took a truck load of metal to the dump. On that one the pulley had worn through the front cover and seized up due to the metal impeller eating in to the rear face of the pump, jamming it's self in there nice and tight. The only reason the owner knew something was going on was a loud screaming sound and smoke as the belt was burning up on the seized pulley.

Now I really wish I had saved that pump for picture sake.

Randy V

No valve damage on that one, Sean?

Either very lucky or was an older non-interference engine.

SeanR

One was S4, other were earlier ones. None of them had the belt break or cams move from TDC so no damage. Owners were smart and knew something wasn't right so they shut it down. Bad pumps tend to make bad noises most times.

M. Requin

Yes, Dr. Coriolis knows the answer...

GregBBRD

I've seen many failures where the water pump impeller comes off the shaft of the bearing and does significant damage to the engine block. Worth noting, this is not an issue with bearing migration, but simply a result of the impeller coming loose from the shaft. There are literally dozens of pictures of this damage....on this forum alone.....so the water pump impellers do continue to turn and do significant damage. There's no mystery or question about that.

I made a custom tool to repair this damage and have fixed about a dozen engines with this damage. I've also loaned the tool out to about a dozen additional people. No mystery or question about that.

I believe every one of these failures and resulting damage (that I've seen) were caused by the Laso "Version 2" water pumps....the one with a metal impeller pressed directly onto the shaft. The "Version 3" pumps had an additional bushing between the bearing and the impeller, presumably to increase the press fit. Sadly, there is no difference on the outside of the Laso water pumps between the different versions....so every single time you see one, you need to remove it and inspect it....a real waste of effort.

All of the problems (I've seen) with the drive pulley coming loose have been with rebuilt pumps.....never seen a Laso or a Factory pump do this.

Bearing migration, for me, is more of an "Internet Myth, as I have not seen this issue.

I believe that Porsche changed to the plastic impeller in 1989.

(As a side note, I've only ever seen two plastic impellers come loose from the bronze sleeve they were made around.)

I've got my own theory of why Porsche made this change...

I believe that any and every "change"...especially a change that requires a part to be made from an alternative material...cost money. (I know what it cost to build a mold for a plastic part and also know what it "takes" to hold in place a knurled metal bushing while surrounding it with plastic, inside a mold.) Therefore I dismiss the idea that the change to the plastic impeller was an "economy motivated change".

I believe that the increased horsepower of the GT series engine resulted in the ability for the engines to change rpms much quicker. This faster acceleration of the engine resulted in the mass of the metal impeller being an issue, which mandated the need for the plastic impeller.

In short, I believe that the mass of the metal impeller, combined with the resistance of the water, became an problem....either mathematically or in testing. Porsche mandated the change, for this reason.

I'm done screwing around with metal impellers. Period. Don't care who makes them. Don't care how cheap they are. Don't care how many work or for how many years they work. If the water pump was self contained and the only possible damage if the metal impeller came loose was to the water pump itself....I would not care. However, installing a portable milling tool (metal impeller) with the potential to machine 2-3 millimeters off an aluminum block in mere seconds is.....well, it makes no sense, to me.

Some (many) of the engine blocks, for 928s, are getting very difficult to find. (I've got clients that are actively searching for GTS blocks to install in their own GTS.) How about a metal impeller in your matching number collector 928 block? Putting a metal impeller onto one of these blocks makes no sense to me.

I'm simply not interested!

The following is a personal statement. I'm not "Troll" fishing, not poking at anyone. If anyone has a different opinion, that's fine. I respect their opinion, for what it is. Alternatively, you can respect my opinion. We don't need another thread ruined with and argument about tensioners.

I like the design, function, and history of the stock tensioner. I use the stock tensioner, whenever possible. I will use a PK tensioner on an early 2 valve non-interference, non adjustable cam timing car....if the stock pieces are all junk and the cost of putting it back to stock is too high. Otherwise, I use a stock tensioner. I will not install a PK tensioner on a 4 valve engine, for 3 very specific reasons....which have been discussed at length and never resolved. The end.

FredR

I now have 17 years/100k km of ownership experience under my belt, far less than some and nothing compared to our resident professionals. In that time I have experienced two water pump failures on my 1990 S4 motor.

The first failure was to the factory fitted pump, the original I believe with a plastic impeller that migrated from the shaft. No signs of any bearing issue or seal leak problem. No idea whatsoever why it failed at approx 10 years of age and some 84k km. The second pump was a rebuilt item supplied by our friends at Devek, it saw two timing belts over some 13 years and approx 80k km and when it failed again the plastic impeller migrated and the bearing/seal were still perfect [as I could tell].

I am sure glad that when they did fail they were pumps with plastic impellers. The thrust on the impeller pushes it back into the pump body so not a natural force to want to push it off the shaft,but for the pump to work efficiently the clearance between the impeller blades and the casing has to be minimal. When the impeller is in the process of failing, I suspect it cannot move towards the pump body so it has to lift off the shaft and thus contact with the casing material.

When the 928 was introduced in 1978 Porsche had little to no experience with water cooled engines and presumably had a big learning curve. Assuming the original water pumps had a service life of 10 years MTBF [mean time between failures], this might explain why around 1988 they had a spate of metal impeller water pump failures that damaged/destroyed the casing and thus forced them to change to plastic impellers - most certainly not a cost based decision.

On industrial pumps, the sizing facilitates installation of what we call "wear rings" on both the casing and the impeller. Thus when a pump bearing fails, contact initially happens wear ring to wear ring and in a well managed plant, the vibration will be detected and the pump is repaired before any serious damage happens. It does not take much metal loss to trash the pump hydraulics given the tight clearances need to support high hydraulic efficiency- usually circa 85% in water service.

Had Porsche been a bit smarter they might have introduced a casing wear ring - in effect what Greg's repair does after the fact- but that is severely constrained by the circumstances of what is there to start with once damage has occurred. I was most impressed by the lateral thinking Greg put into this repair procedure but by then it is mitigating the cost of a new casing and the $$'s to fit it. Had Porsche considered this type of failure in the original design, it would be interesting to visualise how they might have gone about such. Perhaps something "push in" along the lines of the rear seal on the thermostat housing?

Beyond that, given the water pump cost/availability issue, I have concluded that a new timing belt should not necessarily constitute "end of life" for a water pump. However, I have concluded that a "wise owner" should consider replacing the timing belt every 6 years [irrespective of mileage] and every 12 years replace the water pump to avoid breakdowns in the middle of nowhere if like me you are not doing mega mileage. If you are covering a lot of ground then such might be controlled by 50k miles for the belt and 100k miles for the pump.

Regarding rebuilt water pumps, I see no logical reason as to why they cannot be rebuilt but like anything else I would want it to be done by a Greg Brown type of fastidious character. However, if such cannot be realised without charging new pump prices then the outcome is obvious. The rebuilt pump that Devek sent me many years ago did OK as I am concerned considering it cost me something like $110 if my memory serves me correctly but I have no idea who did the work for them and trusted their judgement.

My current Laso pump will hopefully serve me another 10 years [currently 2 years old] assuming I am still capable- time will tell and if I get any less than 6 years total service from it I would be disappointed.

Would I fit a pump with a metal impeller- not if I can possibly avoid it. I must say I am completely baffled by Laso having provided such and then to drop it yet still make pumps with a plastic impeller [correct?] for earlier models. Doubtless Roger may know what the logic behind this is but given the market for these pumps logically has to be about equal amounts of both it makes no sense to me to market one and not the other unless I am missing something here.

Rgds

Fred