Water pump impeller blades scraping

[blue2000s]

I'm half way through replacing my water pump. I figured 12 years is probably pushing it. It's not that hard to take off with the car on jack stands. I pulled it out through the opening in the passenger compartment.

What I found was that the bearing feels nice and tight, no play at all, but it looks like the little finger of the gasket was bent into the impeller and scraped away the outer edges of the blades. I thought this was interesting enough to share.

Don't freak out that my coolant is green. I put in an additive that turned the pink to green so that I could track down leaks with a black light.

Scraped Blades



Bent Gasket, I didn't bent the finger out, it was like that



New water pump


Question: the idler pullys has a slight bit of rock to them. They don't grind or squeak at all. How much play is in a new idler?

[Steve Tinker]

There should be no play in the idler (or tensioner) pulley bearings.
The bearings themselves are replaceable, but you can opt to buy the complete pulley from Porsche - being a cheapskate (my father was a Yorkshireman) I replaced just the bearings in the pulley housings....
Be aware that after replacing the waterpump and belt, there is a good chance that the idler / tensioner bearings will fail due to the extra tension on them: don't ask me how I know !!

[Frodo]

That's kinda weird. The "little finger" part of the gasket---that should have been covered by the base of the water pump, right? If that's the case, how could it have bent out like that, scraping the blades?

Are you sure that finger didn't just stick to the pump when it was removed, bending outward at that point? Of course, if that's the case, it's hard to explain the grinding down of the impeller blades.

[blue2000s]

Originally Posted by Steve Tinker

There should be no play in the idler (or tensioner) pulley bearings.
The bearings themselves are replaceable, but you can opt to buy the complete pulley from Porsche - being a cheapskate (my father was a Yorkshireman) I replaced just the bearings in the pulley housings....
Be aware that after replacing the waterpump and belt, there is a good chance that the idler / tensioner bearings will fail due to the extra tension on them: don't ask me how I know !!

I found a couple of places that sell just the bearing. $20 each so not expensive. Does anyone have any specific places they like to get them?

[blue2000s]

Originally Posted by Frodo

That's kinda weird. The "little finger" part of the gasket---that should have been covered by the base of the water pump, right? If that's the case, how could it have bent out like that, scraping the blades?

Are you sure that finger didn't just stick to the pump when it was removed, bending outward at that point? Of course, if that's the case, it's hard to explain the grinding down of the impeller blades.

I thought of that but the aluminum surfaces that were exposed to coolant are a little darker than the surfaces that were dry. The surface that should be covered by the finger is dark. I think it was bent while assembled. There is no play in the bearing at all, so I don't know what else would have scraped the blades.

[JFP in PA]

The impeller is not scraping on anything, what you are seeing is tip erosion caused by cavitation forming at the vane tips at higher RPM’s, which is a normal event for these pumps.

[blue2000s]

Cavitation makes pits, not scratches.

[JFP in PA]

The bits breaking off during cavitation create the scratches as they drag across the vane tips...............

[pothole]

Originally Posted by Frodo

Are you sure that finger didn't just stick to the pump when it was removed, bending outward at that point? Of course, if that's the case, it's hard to explain the grinding down of the impeller blades.

Yup, that's what I think happened, too.

[blue2000s]

Originally Posted by JFP in PA

The bits breaking off during cavitation create the scratches as they drag across the vane tips...............

Maybe...

See how it is discolored where the tab would be. Is that something you typically see?

[JFP in PA]

No, not really, it says the gasket was not correctly in place. But I have seen the same type of vane erosion (and worse) on pumps where the metal gasket was were it belonged and could not have been a factor in the vane wear.

The only way to know for sure if the gasket was a factor is to remove it, lay it on the old pump, and see if the gasket "finger" can reach far enough to have casued the wear, and the gasket itself should be beat to Hell as well.

[Steve Tinker]

I agree with JFP - in fact, the gasket "finger" would have worn away completely if it was in rubbing contact with the impeller vanes - one very thin sliver of steel causing all that damage to six seperate vanes seems extraordinary.

[Dale_K]

I think there is a certain amount of thrust load on the pump shaft when it's working in the car - think of a boat propeller. The water pump is sucking from the rear and tends to draw the impeller in towards the motor. Is there any fore/aft play in the shaft?