cavitation- a deep dive.

[Geoff Weeks]

Not to muck up Larrys 300 build thread any more I am going to start an new one.

1st I would like to say that I wasn't trying to be disrespectful to anyone (esp Paul) but did want to understand the thinking.

I did a deep read on the subject, and found we are both wrong. Liner cavitation has nothing to do with the water pump at all. Not design, not placement on the block, not how well it bleeds itself of air, nor air itself.

We were both partially correct and partially wrong.  Paul is correct that vaporized coolant, not air, is the cause. It isn't due to flow or pressure however, according to what I have read on the subject.

 Liner cavitation is caused by high frequency sound wave from the liner itself, cause by the combustion and movement inside the liner. When these high frequency sounds get transferred from the liner into the coolant, they make high and low pressure points in a wave, as the liner resonates. When at the low pressure stage of the wave the coolant can vaporize and when at the high they "burst" back to liquid.  This, over time can etch the liner in a tale tail pin hole shape. 

 For this reason, cavitation damage is limited to one plane of the liner, and 90 deg around the liner there will be none, it is all in how the liner resonates.  This also explains why it occurs more or less evenly across all liners in the engine without regard to how close or far they are from the water pump. If it were caused by vapor pockets circulating in the coolant, we would expect the damage to be random around the outside of the liner. It is also why some manuals state "with minor cavitation damage, the liner can be reused if turned 90 deg in the block".

Centrifugal pumps can not pump air efficiently and even less so with a liquid "head" above the outlet. As stated it is why they are not "self priming".  For this reason, there is a way provided to expel air when the outlet is below the top of the impeller housing. Eliminating any trapped air is important, but has no effect on liner cavitation. It can effect the pump itself and other parts of the engine. It is partially why all trucks for over 50 years use a "bottom fill" system (shown in the 300 thread as a Marmon attachment) so the coolant rises from the lowest point in the engine and pushes out the air as level rises.

Paul stated "I must have an open mind to learn" and I do, which is why I ask anyone to back up their statements, I can't learn if I don't know the "why". An open mind lead me to a few hours of reading on the subject. I have already apologized to Paul in the 300 thread if I seamed a bit too "confrontational" but I need to understand the "why" of something to be able to retain it. His 

If you want more info or possibly a better explanation then I can give, do a web search for "causes of liner cavitation in heavy diesel engines" and select the ones Not from some YouTTube, but from engine mfg.  

To quote Paul "

 

So cavitation occours when the liquid, in this case water, separates into gasses

Oxygen and hydrogen in the case of water

This happens when the delivery side of the pump isn't restricted enough or supply side is to restricted "

It isn't that the coolant separates into Oxygen and Hydrogen or even that the mixture of antifreeze separates at all, but rather that it changes from liquid form to gas form while still being coolant, this happens at the minute scale where the wave caused by the high frequency sound from the liner meets the coolant on the outside of the liner. Much like an ultrasonic cleaner does.  It does this while at pressure inside the block. Cummins low flow has a block coolant pressure of ~45psi @2100 rpm! That engine still has liner cavitation issues. It isn't that the flow is restricted in any way, either on the low pressure or high pressure side. 

Until I read up on it, I never really gave a thought to why it is on one side of the liner and 90 deg it doesn't happen, I knew that to be true, both from reading and pulling liners out of engines, but now I know the "why" and it help me to better understand the problem.

Likely more than most want to read or know, but I did put in the time to understand it.

The most important point I learned is the "vapor bubble" is both created and destroyed at the liner itself and not the result of being moved about by the circulation of the coolant. 

Edited 3 hours ago by Geoff Weeks

[other dog]

That's what I thought, I just didn't say anything...

 

 

 

🤣 

All I know is that I went to the dentist one time and he said "you have a cavitation here, you need to cut back on the M&Ms" 😀 

[67RModel]

So based on this analysis what is the conclusion as to why some engines suffer more so than others due to cavitation issues? Is it the specific harmonic that a particular engine creates inside of itself as well as the engine's specific liner design / material?

Also does cavitation affect parent bore engines? Or does it but there is so much material between the wall of the water jacket and the wall of the cylinder that it never becomes a problem?

Edited 2 hours ago by 67RModel

[67RModel]

I was considering purchasing a 40-60hp Ford farm tractor of mid 1980s to mid 1990s vintage. They all had the same 3 or 4 cylinder wet sleeved engines. And from my research there was was repeated mention of cavitation and/or "porous blocks" in those series/vintage of Ford tractor engines. I don't know if those two terms are synonymous or different issues that are conflated by people that don't actually know. Anyway I decided I didn't want to take a chance on something that was coming up on 40 years old that had known issues when they were brand new.

[Geoff Weeks]

4 minutes ago, 67RModel said:

So based on this analysis does what is the conclusion as to why some engines suffer more so than others due to cavitation issues? Is it the specific harmonic that a particular engine creates inside of itself as well as the engine's specific liner design / material?

Also does cavitation affect parent bore engines? Or does it but there is so much material between the wall of the water jacket and the wall of the cylinder that it never becomes a problem?

I went looking for the causes, not solutions but you bring up good questions. I would add one more, does a dry liner engine have a similar problem as a parent bore? Do either of them have a problem at all? You don't hear much about dry lined engine leaking coolant between the dry liner and block/crankcase. I know it happens with freeze cracks.

It would follow that the places in the block that hold the liner would effect the resonance of the liner. So a liner pressed in at the very top and bottom might resonate differently than one with the top press fit is lower in the block.

The irony about learning is: the more you know the more questions it brings up!

Mostly I hear about it in wet lined engines, but those are often the most powerful engines as well, so the cylinder pressure and piston speed may be a factor? 

I bet there could be a collage level course on the causes and solutions alone!

[mowerman]

lol I have no argument,,, here… I’ve never even heard of an air pocket in the water pump till now… like most people… assuming after running an engine a few minutes after new water pump ,,, air is all pushed through to the radiator 

[Geoff Weeks]

7 minutes ago, 67RModel said:

I was considering purchasing a 40-60hp Ford farm tractor of mid 1980s to mid 1990s vintage. They all had the same 3 or 4 cylinder wet sleeved engines. And from my research there was was repeated mention of cavitation and/or "porous blocks" in those series/vintage of Ford tractor engines. I don't know if those two terms are synonymous or different issues that are conflated by people that don't actually know. Anyway I decided I didn't want to take a chance on something that was coming up on 40 years old that had known issues when they were brand new.

IDK, I know a neighbor had a problem with a IHC. It was wet lined . Coolant filter and SCA's were the std answer in trucks at that time. He, like many farmers never gave it any thought until there was a problem. Never used SCA's or coolant filters. 

[Geoff Weeks]

2 minutes ago, mowerman said:

lol I have no argument,,, here… I’ve never even heard of an air pocket in the water pump till now… like most people… assuming after running an engine a few minutes after new water pump ,,, air is all pushed through to the radiator 

If the MFG was any good, they likely would have done the "thinking" for you and provided a way to vent most if not all the air. Cat 3406 has the bypass to the 'stat come down vertical, so a small hole at the top of the higher pressure side will vent to the T stat housing. 

 If the mfg did provide a method either internal or external, it is important not to plug what they put there.