Strosek Ultra

Referring to Mr. Brown's love of economical water pumps I have to share the following.

Some time ago I spoke with Frank Herrmann at GEBA about the Porsche 928 water pumps and the problem with metal impellers that damage the engine block. GEBA is a very large supplier of water pumps to the german auto industry. This is his answer translated from German by Google.
Åke

We know of the pumps for the 928 and we have heard of these problems too.
We haven't had this problem with our pumps yet, as the impellers are pressed onto the shaft with great force and can no longer change their position.
In addition, our dimensions are always approx. 0.2-0.3 mm below the original dimensions.
We can imagine that this problem is caused by a worn out bearing shaft!
There is then a movement both in the axial and in the radial direction, which with the small gap dimensions then leads directly to contact with the engine block.
But of course these are only assumptions, as we have not yet seen a pump where the impeller grinded on the engine block.
The main reason for using plastic is certainly that no post-machining is necessary!
I mean that in relation to the dimensions of the impeller itself and also in terms of the distance to the engine block! (see drawing in the appendix).
This increase does not affect the efficiency of the pump at all!
External tests on pumps with a similar design have shown that a change in efficiency only occurs at a distance of more than 1.5mm.
the distance with the OE pumps is normally between 0.4-0.8 mm!
There is absolutely no need to worry about the efficiency here.

FredR

Åke,

Some interesting info there. When I was trying to evaluate the cooling system performance many years ago the biggest problem I had was not knowing the water pump performance curves. If as the GEBA chap states the clearance can be increased to 1.5mm before efficiency suffers then all I can say is that it confirms my suspicions that pump efficiency must be very low- somewhere in the order of 20% hydraulic efficiency I suspect. Given the hydraulic duty is very small this is of no real world consequence.
At least with that impeller dwg I should be able to estimate the pump performance curves given Covid boredom if I can find my pump design handbook! I assumed the pump might be delivering about 150 litres per minute at 6k rpms and a head equivalent to 10 psi so if by any chance you have the GEBA pump curves in your files that would be very informative to me.

For those that may be interested a pump delivering 150 litres/min and developing 10 psi head at an efficiency of 20% will need just over 1HP to drive it- I suspect that number will not be too far off the mark unless my ability to calculate such has fallen off a cliff!

My first Porsche OEM water pump failed 20 years ago at about 85k km. I then fitted a rebuilt water pump from the States and that failed after about 60k km. On both pumps the plastic impeller left the shaft and the bearings were fine - the impellers did not hit the casing- they formed cracks in the hub and let go. I do not know what a reasonable life expectancy is for pumps but I might have hoped for 100k miles on a Porsche OEM pump. I currently run the LASO pump with plastic impeller so we will just have to see how that fares.

For sure a steel impeller can be pressed on much tighter than a plastic one- whether we should believe what GEBA say is another matter. Experience is what counts and whereas it would be good to know of such in a positive light I feel I would need more convincing before buying in to the concept at this moment in time.

buccicone

Should start a survey “sticky thread” on Geba/Laso/OEM just like the 996 Forum with IMS failure.

ROG100

I sold one GEBA pump and it failed withing 6 months and I had to replace it under warranty - not a good track record.
Most issues with the metal impeller moving on the shaft were related to older designs and rebuilds of rebuilds which compromised the interference fit. Mostly over 5 years ago.
Porsche, and then Laso, changed to plastic impellers. I have not seen or heard of one instance on either of these pumps where the impeller has moved on the shaft.
Laso pumps, (because that is all I sell) based on the quantity I have supplied, and the reported failures represents less than 0.25% failure rate. While not perfect is still pretty dam good.
The failures all were leaks from the cartridge seal and evident by coolant seeping from the weep hole.

Retail wise - no one buys a Porsche pump from us, even though we offer them on our web site. So I cannot offer any comment regarding their track record. I have no reason to doubt that they are good, as GB states.

Jerry Feather

I wonder why the iron (I think it iron) impeller and maybe even the pulley can't simply be pinned to the shaft?

dr bob

The impeller "moving" is some combination of impeller actually losing grip on the shaft, and the shaft itself moving as bearings wear and finally fail. Greg shared a bit of guidance, saying that the outer (drive end) needs to be supported by a roller bearing, while the inner (impeller) end needs ball bearings to manage thrust. As mentioned elsewhere, the switch to plastic impeller was to mask the symptoms of poor bearing selection in the design.

I also wonder how much to the drive-end radial load is from static tension from the belt vs. dynamic tension from the crank trying to spin the pump via the belt. The pump is driven by the back of the belt so there needs to be enough total tension to maintain adequate friction for the pump drive. But no more.


For the impeller slipping, I can't see why a rollpin couldn't be fitted there.

The Forgotten On

The new Porsche pumps have always been good as far as I can tell. My 81 still had the original one working just fine until the head gaskets went after 37 years and 160k miles.

However now we have the choice of a few suppliers that sell plastic and metal impeller pumps.

I personally do not think the aftermarket pumps are held the as high of a standard as original OEM Porsche pumps. That however is my opinion based on my own experience and my observation of the castings.

As such I would never fit a metal impeller pump due to the possibility of it machining the volute in the block. The worst that can happen with the plastic is that the impeller eats itself or falls off the shaft.

This was mitigated as far as I'm aware by the extra bronze bushing present in all the new plastic water pumps.

As others have stated it would have been nice if they stuck the proper spec bearing in the first time so they didn't treat the symptom and instead treated the cause of the pump failures outside of the seals failing occasionally.

Strosek Ultra

Fred, I do not have any further technical information concerning the GEBA pumps.
I once checked the distance between the plastic impeller and the engine block using model clay. The pump was Porsche original and the gasket all new 0,5mm thick.
I found the distance to be 1,0 to 1,1 mm.
Åke

GregBBRD

All water pumps fail, sooner or later.

Anyone that sells or installs water pumps on a regular basis needs to figure out what works for them...and follow that path.

Roger sells Laso and has a low failure rate. I can't get one to last for 30,000 miles and got tired of "eating" the labor to change them.


928 International sells Geba and Mark Anderson says he has very low failure rate. I've seen so many blocks damaged from cast iron impeller, I can not bring myself to use these.

I sometimes can "miss" the obvious, but if all that was required for Porsche to continue to run a metal impeller in 1989 was to tell their manufacturer to "tighten up" the impeller press fit, it seems like they would have tried that....

I've had tremendous success with factory water pumps, so I encourage my clients to use them (I discount them so heavily that I could make more money selling a Laso, BTW.)

For the people that are changing a water pump on their own cars:
​Muddle through the information and do what makes sense, to you.

rexpontius

Hi Greg, what is the failure point you see on the Laso pumps? is it the bearing that fails or does it develop leaks? Or even worse the impeller comes loose from the shaft.
I installed a Laso pump in my 86.5 rebuild project and the life expectancy you mention makes me worried :-)

thanks
Kind regards
Michel

chart928s4

At this point we should know the OEM supplier(s) for 928s. Porsche certainly doesn't make their own. Every major parts maker sells water pumps. Most OEMs have at least 2 suppliers for critical parts though Porsche seems to have had mostly Bosch parts in the 928 days. Bosch makes water pumps, but so do Magna, Conti, Delphi, Denso, Hitachi, Aisin ... who is it?

ROG100

IIRC I found the original water pump (a few years back) supplier in Germany - GPM - only supplier that I am aware of.
I talked with them about the 928 pump but they would not sell to the aftermarket - only Porsche.
Rebuilds were done here in the States and suffered the same issues as other aftermarket 928 pumps.

GregBBRD

On the most recent Laso, with the plastic impeller, just leaks and bearing failures (once the bearing gets "steam cleaned" by the seal leaking, failure from the grease being washed away doesn't take very long.) I wish they would identify the most recent version with some sort of external marking. Without this, I'm pretty much forced to remove and inspect any Laso I see, to make sure there is not one of the "early" versions with a metal impeller. And once it is off....is it worth the chance to re-install it, regardless of which version it is?
The good thing....I have not seen a plastic impeller come loose or fail. Have not seen the drive pulley come loose. They seem to have that figured out.

rexpontius

Thanks for the info Greg, will keep an eye on it. Fingers crossed :-)

chart928s4

Thanks Rog. These guys I guess. I never heard of them but they are pretty big ($3B in auto parts sales). https://www.nidec.com/en/corporate/n...oup/nidec-gpm/