Water Pump Carnage
 

I'm starting another thread here to go along with my Head Gasket thread but this topic deserves its own space.

Last night after removing the Jesus bolt (to change broken lower timing chain guide) I found what has probably caused all this mess and that the entire head gasket replacement MAY not have been necessary.

Obviously for an overheating car, the water pump should have been at the very top of the list of things checked. Because it was such a requisite check, I relied on TWO different auto shops to tell me that the water pump was not the problem. I would normally would have assessed this myself but the car had to be towed and I didn't have access to it.

One (a very well known BMW tuner shop in town) had the car for a week and I got on the phone with the acutal service tech several times. I now assert that he lied straight to my face about what he had checked/observed. In any case, the end assessment was 'bad head gasket', notwithstanding his direct quote "you have the metal impeller water pump so I know it's not that".

Ultimately, whoever the fault goes to...we all missed the forest for the trees.

From what I have researched, most of the stories you hear about BMW water pumps with plastic impellers exploding refer to the molded plastic models in the early 2000's. But I think BMW switched to PPS Composite a long time ago. So the Genuine BMW Water pump (Saleri I believe) with a composite impeller is considered perfectly robust and and much more reliable.

Here's the Saleri I just pulled out with 18k miles on it. Granted, the car did 'overheat' at one point but I just can't IMAGINE what would cause this type of destruction. Even if there were a manufacturing defect, how does the wheel get sheared into two halves like this?

Further and perhaps more worriesome, I have to figure out how to locate and remove the plastic chips that are floating around in the cooling system. Anybody got experience with that?

https://i.postimg.cc/76cJKPBw/6pump.png

well, leave it to Xoutpost to come up with the best possible answer I have heard to date as to why this happened.

Cavitation

https://xoutpost.com/1103127-post10.html

by our very own TiAg5.

repeated 'loss of coolant' caused cavitation around the impeller which was not designed for the shock waves cavitation produces. (if I am reading this correctly).

- Re broken plastic pieces...I guess you can use a small vacuum to suck it out.

- Or use a garden hose and flush it.

- Re WP: I have been happy with HEPU, the HEPU in my 1998 528i was installed in May 2006 at 90K, it is now at 185K and still fine, I plan to replace it soon.

- Plastic impeller was used to save weight by BMW, but used in the "wrong" place. This is not a place to put plastic in there.

I wrote the cooling overhaul for my 1998 528i years ago.
Scroll down to Step #11 to see how the garden hose was used:

ENTIRE COOLING SYSTEM REPLACEMENT Tips and Tricks (Very Long, Enjoy!)

Thanks for the tips. this is very helpful. whether i am able to pull off this level of 'flush' remains to be seen as the car is currently in the garage, which i will not be able to flood.

This may be a situation where i have to get it running, then do some of this cleanout later. That said, given the manifold and cylinder head are off, i am hoping i can drain the block drain and see some plastic come out. Who knows.

i will probably wait on doing an extensive and thorough cleaning of the cooling system mainly because i first need to know if these head bolts are going to hold. If they don't, this car goes to the junkyard.

i DID find a couple of chips that had drained from the radiator...but certainly not the balance of what is missing.

another interesting note: I just picked up the OE Saleri water pump at Napa this morning. it's in a Saleria Italia box and the impeller has GERMANY stamped on it and the little circular date code like on all the other BMW parts. I was kinda shocked honestly. Unfortunately it was $80, but when i get my warranted Saleri pump back from FCP, i may put that one in the Napa Box and return it ;)

Flush the system with hose on reverse. Eg into the outlets from the heater cores. You'll recover most of the offending bits that can cause a problem.

You may be able to add a strainer in some location to catch pieces that get dislodged after engine is back together.

Very good thread to share as few people are going to think of impeller self destructed as a cause of overheating

cavitation is often the cause of serious impellor damage, however it is often and the end of the blades and not the middle. There's not enough detail in the picture to assess that, you should be abe to see a porous surface at leading edges or inside corners where the vacuum bubbles impode and chip away the material.

in this case a bad fit in the pump housing and/or debis between impellor and housing seems possible too

@Russianblue I hope you're not serious about pulling the switch and return. I've been on the loosing end of that a few times. NOT cool.

He's saying putting identical brand new part in the box. Not a janky clone. He bought a local copy but will get an identical one he won't need anymore from warranty.

@RB you can also return the FCP part for store credit vs. new part. (you prob have to print and fill out the form vs. use the online form).