Cavitation damage

[sdwarf36]

I know its a concern in the 7.3 Ford Diesels-and a few others-but i never read anything about VWs suffering the same phenomana. Heres the inside of the water pump on the motor i'm doing. its NOT from the impeller hitting-its a bunch of little craters- no scraping at all.

[rabbitman]

Was that running a cast or stamped impeller?

[maxfax]

Was that running a cast or stamped impeller?

X2 on that....   I have a few of those around that are cavitated. The pits aren't typically the whole way around...  A stamped impeller bouncing around in there more typically causes marks like that..  The Cast impellor coming loose generally makes the scrape marks..     It could still be cavitation, that particular piece is a somewhat low grade aluminum casting I believe...

[sdwarf36]

Its the iron impeller. I'll get a better pic-but they are definitly holes + not scrapes. Theres even a few down in the neck of the pump-where theres no way an impeller could touch.

[truckinwagen]

I will bet that it is corrosion and not cavitation, I doubt that the pulses from combustion would do that kind of damage there without destroying many other parts of the motor first.

the aluminum used in the cooling system of our motors is very susceptible to the acidic nature of an unkempt cooling system, I have seen thermostat outlets eroded all the way through from corrosion caused by many years without a coolant flush, or even change.

[dyoungen]

sdwarfe36: The cavitation that happens on the Ford 7.3 happens on the cylinder walls, not the water pump. I have a 6.9 and due to the thicker cylinder walls I don't have that much to worry about like the 7.3

[maxfax]

I will bet that it is corrosion and not cavitation

Bingo!  That's the word I was looking for earlier..   IF you have holes the whole way down the neck I'll bet that's definitly what happened..   

[smutts]

My bet is that it is a combination of the two. Looks the same as my water pump.
Possibly the cavitation isn't enough to eat the metal directly but it could be enough to disturb the anti-corrosion mechanism/ chemistry of the antifreeze, allowing corrosion. Or Not!

Did you ever drive the car without a pressure cap? Doing so allows horrible things to happen with cavitation.

[sdwarf36]

The more I read about cavitation, the less likely that this is what it is. Everythnig pointed to cylinders-mainly wet sleeve-resinating with combustion cycles shooting air bubbles off them + bouncing about the water passages.
 Whatever it is-sure looks strange. "bout the only thing I am sure of is it not from the impellar hitting.

[truckinwagen]

again, it looks like erosion due to an overly acidic cooling system.

if the coolant is not changed often enough it can get quite acidic and eat all sorts of parts, I saw a subaru head that the coolant had eaten through the head into the intake runner, hydrolocking the motor(all the aluminum cooling system parts were heavily eroded) but it was driven close to 400,000 miles without EVER changing the coolant.

and remember a good flush is necessary when changing coolant too, get all the acid out!

-Owen

[VW Smokr]

Agree that the damage in the picture looks like corrosion working.

That said, many VW pumps/mounting plates have excessive casting flash in the intake or outflow portions, causing partial restrictions that can exacerbate cavitation. It's very quick & easy to spend a little time with a die grinder, Dremel, drill, etc. and a burr, then sandpaper flap wheel, to smooth out any flash that can impede flow. (Obviously, in smoothing things out at the inlets/outlets, one needs to keep from altering any actual impeller-to-housing wall dimensions.)

Such cleanup has definitely made a difference on several motors I've worked with (VW & non-VW), even to the point of correcting chronic overheating issues. Seems like it allows for the coolant to circulate more easily, thereby making the engine temperatures more even in closed thermostat mode, and reducing heat more quickly once the stat opens.


J.R.
SoCal

[burn_your_money]

Did you ever drive the car without a pressure cap? Doing so allows horrible things to happen with cavitation.

Can you elaborate on this please? Don't you run without a cap if you are using Evans coolant?