Water Pump Corrosion

[totalshell]

hurrah found the post with photos.. http://www.trialscentral.com/forums/index....amp;#entry75662

once i whipped the impeller off the 'corosion/cavitation' was just as bad all around the impeller seal

[b40rt]

Useless piece of information - boat / ship propellers of all sizes suffer from cavitation.

[stork955]

That photo looks like corrosion. Especially as its around the perimeter of the pump housing and has traces of coolant/crusty stuff in it. Cavitation will usually be around the impeller area and quite clean. Nothing to do with boat propellers!

Cheers,

Stork

[b40rt]

That photo looks like corrosion. Especially as its around the perimeter of the pump housing and has traces of coolant/crusty stuff in it. Cavitation will usually be around the impeller area and quite clean. Nothing to do with boat propellers!

Cheers,

Stork

Boat propellers don't suffer from cavitation ! I think you'l find they do.

[slapshot 3]

Any propeller or any sort will suffer from cavitation when it's in water and going quick enough....simple physics really

[jse]

Cavitation is the proper word to describe the problem, not corrosion. Thanks.

I have noticed that most quality motorcycle coolants state; "50/50 cooland and de-ionized water to prevent cavitation".

I'm guessing that the recommendation for de-ionized water is to address corrosion, not cavitation issues. I looked at the photo of the pump housing and based on the areas of damage I'd guess corrosion, not cavitation (the process of formation of vapor bubbles of a flowing liquid in a area where the pressure of the liquid falls below its vapor pressure, and the rapid collapse of the bubbles produces a minute, but locally strong shock wave that can produce pitting). I've seen cavitation damage to impellors (and sometimes at the end of the discharge tube) but usually only the metallic ones, not the plastic ones that are generally in use in Trials bikes now. Perhaps the seam from the o-ring to the inner housing chamber is a good place for metallic salts in the coolant to collect?

Another area where cavitation is a problem on motorcycles is in shocks, which is, in part, why they are pressurized as high shaft speeds will cause cavitation at the piston face. Not such a problem with Trials shocks as the shaft speeds are usually lower (so pressurized to about 140-170 psi) but a real problem with roadracers that run much higher shaft speeds (and are usually charged to 200+ psi).

So, my guess is corrosion due to contaminants in the water.

Jon

[shercoman2k8]

I was fiddling the other day and topped up my coolant with river water, ran it through a filter though! On startup I noticed that the water coming from the overflow turned cloudy when hitting the exhaust, what causes this and is it ok?

[stork955]

I'm guessing that the recommendation for de-ionized water is to address corrosion, not cavitation issues. I looked at the photo of the pump housing and based on the areas of damage I'd guess corrosion, not cavitation (the process of formation of vapor bubbles of a flowing liquid in a area where the pressure of the liquid falls below its vapor pressure, and the rapid collapse of the bubbles produces a minute, but locally strong shock wave that can produce pitting). I've seen cavitation damage to impellors (and sometimes at the end of the discharge tube) but usually only the metallic ones, not the plastic ones that are generally in use in Trials bikes now. Perhaps the seam from the o-ring to the inner housing chamber is a good place for metallic salts in the coolant to collect?

Another area where cavitation is a problem on motorcycles is in shocks, which is, in part, why they are pressurized as high shaft speeds will cause cavitation at the piston face. Not such a problem with Trials shocks as the shaft speeds are usually lower (so pressurized to about 140-170 psi) but a real problem with roadracers that run much higher shaft speeds (and are usually charged to 200+ psi).

So, my guess is corrosion due to contaminants in the water.

Jon

Gday all, good explanation! So the upshot is that if you have a hole in your water pump, check out the underlying cause first - corrosion is a coolant related issue and can be sorted, cavitation is something we just have to live with. Unless you can re-design your pump. Its interesting to note that plastic housings and impellers dont seem to suffer from cavitation damage, prehaps this is because the plastic is more pliant and can absorb the shock of the cavitation where the alloys resist and suffer. Anotther important thing to keep in mind is that most manufacturers recommend a flush as part of coolant changing, this is possibly to help remove corrosive deposits from area like the joint face of the water pump where it collects and "sits". Either way though we end up with a hole when it goes bad. At least Aluminium is repairable to a certain extent.

Cheers,

Stork

[baldilocks]

I was fiddling the other day and topped up my coolant with river water, ran it through a filter though! On startup I noticed that the water coming from the overflow turned cloudy when hitting the exhaust, what causes this and is it ok?

You have probably overfilled the system and water is not recommended as far as I know.

drain the system, it takes about 5 minutes, and replace with a coolant suitable for Aluminium engines with a corrosion inhibitor

[peterb]

Had to add my tuppence worth here - more so for Stork really, I used to size up and specify Fisher control valves for various petrochemical fluid control applications, taking cavitation, or flashing into account as this can cause significant damage in the valve body and downstream piping. Cavitation occurs when a liquid changes state to a vapour state usually from an increase in fluid velocity at the point of or just downstream of the greatest flow restriction. At this point, the flow velocity is at it's greatest creating a substantial decrease in pressure which can drop below the vapour pressure of the liquid creating bubbles that tend to implode on the surrounding surfaces that causes significant surface damage.

What a memory!

I tend to use 100% coolant in my bikes, not adding any water.

Bye, PeterB.

[jse]

Had to add my tuppence worth here - more so for Stork really, I used to size up and specify Fisher control valves for various petrochemical fluid control applications, taking cavitation, or flashing into account as this can cause significant damage in the valve body and downstream piping. Cavitation occurs when a liquid changes state to a vapour state usually from an increase in fluid velocity at the point of or just downstream of the greatest flow restriction. At this point, the flow velocity is at it's greatest creating a substantial decrease in pressure which can drop below the vapour pressure of the liquid creating bubbles that tend to implode on the surrounding surfaces that causes significant surface damage.

What a memory!

I tend to use 100% coolant in my bikes, not adding any water.

Bye, PeterB.

Peter,

have you had any experience with a product called "Redline Water Wetter"? I've use it in my bikes since I had done some research with it in the roadrace bikes I built. I ran straight de-ionized water as they can't use ethylene and propylene glycol anti-freeze in their cooling systems (very nasty stuff when spilled on a racetrack) but with the Redline (used for it's anti-corrosion agents) the telltale temp tapes registered about a 15-20 degree drop in engine temperature and in a couple of the engines I could dial in a degree or two more static ignition advance for better drive out of the slow corners. It advertises that it " doubles the wetting ability of water", so I assume it affects the surface tension somehow. It also says that it "reduces cavitation corrosion" and I've often wondered exactly how it worked (technically speaking). Any ideas?

Jon

[copemech]

In my poor simple mind, the words Magnesium and Water Pumps have never been associated ! You are asking for trouble from the start!

Add other things that occur in nature, and? Then add imperfections in the castings! Lets not even get into electrolosys issues. Yet just hope the 100% concentrations of coolant contain enough corrosion inhibitors to do the job, and for what time? As it is normally these ingrediants that wear out in the coolants in the first place.

Why one will do it and another not?

I do think Peters suggestion of just running 100% coolant may be very viable, as in the trials bikes normally do not overheat, thus require less than optimum thermal transer rates, while corrosion issues may prevail in any bike, and if things do get diluted over time, well? Just a better start.

Who is to say really, may be luck of the draw on some? Yet precautions are there!

[stork955]

Thanks PeterB and JSE, that is how I remember this from trade school - so many years ago - I didnt have the words...

Im no chemist but is it that running 100% coolant will reduce cavitation by "resisting" the low pressure boiling that causes it? And of course being more viscous than water does any "bubble" that does form collapse more slowly and so do less damage? Thoughts? This has never been a real major issue in Car Cooling systems - the ones I am familiar with anyway. I also wonder now if Boat Props cavitate less in salt water than fresh...

Of course the only reason we need to run coolant aside from that is as corrosion protection and anti-freeze (which causes mechanical damage) so I wonder what these "Water Wetter" products hope to achieve. In a pressurized cooling system water boils at around 110C (?F) so what is its real purpose?

Cheers,

Stork

[peterb]

Hi Jon,

I haven't heard of Redline Water Wetter - not since reading about it in these forums that is. If it is to reduce cavitation, as advised, then the physical characteristics of the addittive would be different to plain water, in effect to alter the vapour pressure of the liquid so that it would flash off at a higher (vacuum) pressure - vapour pressures are usually given in terms of psia, psi absolute.

As far as the Redline Water Wetter working to improve thermal heat transfer, I can only guess that it has an improved thermal transfer over water - like metals, copper conducting heat better than steel.

Bye, PeterB.

[jse]

Hi Jon,

I haven't heard of Redline Water Wetter - not since reading about it in these forums that is. If it is to reduce cavitation, as advised, then the physical characteristics of the addittive would be different to plain water, in effect to alter the vapour pressure of the liquid so that it would flash off at a higher (vacuum) pressure - vapour pressures are usually given in terms of psia, psi absolute.

As far as the Redline Water Wetter working to improve thermal heat transfer, I can only guess that it has an improved thermal transfer over water - like metals, copper conducting heat better than steel.

Bye, PeterB.

Makes sense, thanks for your input. I posed the question to a retired Chemical Engineer friend of mine and I'll see what he comes back with.

In other recent research, I came across a water-less coolant called "Evans NPG+" that's used in racing and other specialized engines: http://www.evanscooling.com/html/npgPls.htm . Boiling point of around 370 degrees F. as I remember, and designed to run without pressure (or little pressure) in the cooling system. When I go to pick up some race gas tomorrow, I'll see if I can get some info from one of the racing suppliers and maybe pick up a gallon and do some testing on it in some of the high-stressed four-stroke racing engines (MX & Quads, as you can't run it in the Roadracers) and maybe try some in my poor old 280 Pro test mule. I'm looking for better thermal stability in the four-strokes under racing conditions and since Trials is headed down the 4S path, it might solve some future problems should they arise.

Jon