Dear Professor Nuzanbolts;

I have some questions regarding cavitation and antifreeze. When I search the internet, there seems to be a great deal of confusion regarding these subjects. Cavitation--as I understand it--is a situation in which bubbles are formed when coolant moves through a water jacket. These bubbles can reside  next to cylinder walls and, as they dissipate, they create a vacuum which, over time, gradually erodes away the metal. Concern over this has led to  considerable discussion in online forums; however, there doesn't seem to  be a consensus of opinion. I would appreciate finding out what you think about the following:

Although online discussions seem to pertain to diesel engines, I assume that cavitation affects gasoline engines as well. Right? Some people are of the opinion that engines with wet sleeves are affected  more than engines with cylinders bored in the block. Is that true?

AntifreezeAn opinion often expressed is that engines with turbos are affected more by cavitation than engines naturally aspirated. What do you think?

Are older engines affected more or less than newer ones?

There is much confusion online over antifreezes. Generally, people seem to agree that antifreeze for tractors should contain additives to prevent or
reduce cavitation.  Do you agree?

Many people believe that coolants purchased at WalMart and comparable stores lack the necessary additives for tractor engines. They say that it  is advisable to purchase antifreeze from the companies that sell the tractors (i.e., John Deere antifreeze for a John Deere tractor).

Some forum contributors suggest that the color of the antifreeze indicates which type is preferable--red antifreeze should be used instead of green,  for example. Does that make any sense?

 Regarding the mixture, generally a 50/50 mixture of water and antifreeze  is recommended. However, one of my tractors has a thermosyphon cooling system and anything stronger than a 25% antifreeze / 75% water mix causes the engine to overheat. Does that mean that my engine is more vulnerable to cavitation  than engines with water pumps?

On the other hand, a thermosyphon system moves coolant through the system more slowly than if the engine had a water pump. Does this reduce the possibility of cavitation?

Are some brands of tractors or engines more vulnerable to cavitation than others? In other words, is engine design a significant factor in preventing cavitation?

How common and serious a problem is cavitation? Can it significantlyreduce engine life?

 Finally, is there any way to determine if significant cavitation is occurring in an engine?

Thank you for helping me to better understand this situation and hopefully avoid it.

The Ole Sheepherder
 

Dear Ole Sheepherder;


I am reasonablly sure t First off, the bubbles that we are concerned about are not formed by coolant flow. The vapor bubble is actually formed on the coolant side of the cylinder wall. Vibrations from piston movement and pressure changes in the cylinder cause the wall to vibrate. It does not matter if the cylinder bore is in the block parent material or a replacement liner. Cavitation erosion can occur in either cylinder wall

Now that we have gotten rid of the air bubble and replaced it with a vapor bubble, I need to make one thing very clear. The conditions needed to make a vapor bubble do NOT exist in gasoline engines. At least not yet, but more turbo charging (supercharging) could change that. The higher pressures and heavier components of a diesel engine are what make this a diesel engine only at the present time. A turbo on a diesel only makes the pressure and vibrations worse.

The information that I use indicates that as the bubble forms, it takes a small piece of the coolant-side cylinder-wall with it. It is just a few molecules at a time, but it also leaves a little sharp edge to the metal. That just makes it easier for the next bubble to form. A four-stroke-cycle diesel running at 1800 RPM has 900 ignition and power strokes a minute or 15 ignition and power strokes every second. As newer diesel engines tend to run faster, they may be more prone to cavitation problems. A few molecules removed every 15 seconds means that it won’t be very long before there is a small pinhole that will allow some corrosive exhaust gasses into the cooling system when the engine is running. The extra pressure causes overheating and really nasty coolant being pushed out the overflow. When the ngine is shut off the pinhole allows coolant into the cylinder and on into the crankcase oil. At this point I should remind you that the glycol used in most antifreeze will attack and eat away at the bearing material in the rod and main bearings.

Lets see, overheating and corrosion in the cooling system, rod and main bearings eaten away. All that sounds really expensive when compared to some Diesel Coolant Additive (DCA) or diesel specific antifreeze.

Wal-Mart antifreeze is fine for gasoline engine tractors. Wal-Mart antifreeze without diesel additives is not good for diesel powered tractors, but with some DCA added, then it is fine for diesel powered tractors. As far as I know, the color of the antifreeze indicates the type of antifreeze. Red or orange colored-antifreeze is an organic, acid-based mixture, and a 5 year or 50,000 mile change interval is recommended. Green or glycol-based antifreeze calls for a change interval of 2 years or 25,000 miles. If green is replacing green then change interval should be 2 years or 25,000 miles. I personally use a Digital Volt Ohm Meter to see if I need to change antifreeze. I place one probe in the antifreeze (not touching any metal) and the other probe on any good ground. A reading of 1 (one) Volt or more means that it is time to change the antifreeze.

The thermosyphon overheating is a new to me. I know my Grandfather never put anything but water in his 1939 John Deere model A. He would just drain it anytime cold weather was predicted. I do remember taking the radiator cap off (non pressurized system) after he had finished grinding feed with a hammer mill. There was nothing slow about how the water was running. It was moving as fast as any water pump could push it, and the tractor was idling. Granddad said he was letting it cool down.

Engine design doesn’t seem to effect cavitation that much. How big of a problem is cavitation? Well if you have a fleet of semi tractors and you are hoping to get 1,000,000 miles on them before you overhaul them, then cavitation is a big concern even if you are just hauling feathers. The only way to tell if you have a problem is to tear it down and look. If the cylinder bore is in the block parent material then a bore hole camera will let you look for pinholes. Of course if you find pin holes, it's a little late.
that the same people that do oil analysis probably offer coolant analysis also. Just don’t ask me how much it costs, as I simply change the oil often.

The now retired Herr Professor Nuzanbolts