Cavitation?
 

I was just wondering if there is a cavitation issue, that anyone knows of, with engines such as the 617 etc.?

Ive never heard of it
 

I've read about the cavitation issues with truck diesels, cummins, freightliners etc., but i have never heard it mentioned at all associated with mercedes auto diesels. I'm sure that the MB coolant is the same for all MB cars, gas or diesel, so I doubt that it has the anti-cavitation additives (SCAs) needed for american diesels.

I suspect this may have to do with how the coolant circulates within the engine, and how the coolant contacts the cylinder sleeves, but I dont know enough about this stuff.

My understanding is that "cavitation" is the phenomenon whereby coolant becomes super heated in microscopic portions of the coolant and boils causing a microscopic vapor bubble which instantly dissipates...this results in super high pressure at the bubble ...as this occurs where the coolant contacts the cylinder sleeve, the extreme physical forces result in microscopic corrosion and development of pores in the sleeve, eventually resulting in coolant penetration into the cylinder. (or something like that?!?!?). Does the coolant in MB diesels not come into contact with sleeves??

Anyone else know about this??

Cavitation can be a problem in any "wet liner engines", ones where the cylinder liner is in direct contact with the coolant. I've only encountered it in Catapilar and Cummins engines. The om617 engines are "dry liner" and do not have a problem with cavitation. Do not! use any of the anti cavitation addatives in an MB cooling system as they tend to form a layer of minerals on wet cooling system surfaces. This can inhibit heat transfer.

I figured there wasn't a problem with MB engines, just wanted to know if anyone thought or knew different. Cavitation seems to be a big problem with many of the newer US diesels. Ford (International), Cummins, Cat, etc. all seem to have a problem if the SCA's aren't monitored.

I would think the first place for cavitation to occur would be in the water pump impeller, on the suction side of the vanes/blades. The next place would be where there were significant flow discontinuities in the coolant passages. After that you might get something better described as two phase cooling, which is something that improves the heat transfer capability of a surface. The thermal management of the engine may have been designed to take advantage of allowing microscopic steam bubbles (phase change) to occur on the surface of the cylinder wall. Before the bubble can grow to a significant size, the flow through the area washes it away, and as it surrounded by cooler water, it collapses. As soon as the bubble leaves, another is formed. Designing the cooling system to take advantage of this phenomena will allow a smaller surface area to remove a given amount of heat. It may also require higher fluid velocities, which would allow a smaller total fluid volume. Each of these would save weight.

That it might also cause difficulties with the corrosion life of the cylinder liners is an indication that the engine was designed to take maximum or maybe too much advantage of this concept. If the fluid velocity is sufficient to wash away the steam bubbles as they begin to form, and the bubbles collapse in the bulk volume of the fluid, there should be no real problem. If the bubbles collapse on the cylinder wall, they can act to erode the oxide layer away as this is typically less adherent or hard than the base metal. Since there are no oxygen depleting chemicals in normal anti-freeze, another oxide layer forms immediately, is removed, and so on. The process of forming corrosion/erosion pits is started. If this is happening at a steady pace, it will also generate current flow that makes dissimilar metals extremely unfriendly to each other, and you get galvanic corrosion as well.

It would seem the head would have the highest temperatures, and have the greatest problem with two phase flow issues.

Anyway, this is an interesting thread, and for those of us who have never heard of SCA's, like me, what are they?

Have a happy New Year, Jim

SCA=supplemental coolant additive, this is what prevents cavitation in engines that have a problem with it.

Evans says there waterless coolant has no cavitation problems.

See Evanscoolant.com

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