I went to my local Ford dealer, and they had no idea what cavitation was. They thought the additive was to prevent rust. So I went a few towns away to a Ford truck dealer. They said the older trucks should have the green. The newer trucks should have the other light color coolant because the seals were different. They said the older truck seals would not handle the newer coolant. So who is right?????????They also said the green they sell is made by Texaco and is the same you buy at Pep Boys or AZ etc. I still have green in mine with the Motorcraft additive, because It was just changed before I got the truck not long ago. I use the test strips and it looks fine. This is my first diesel so I have no past experience with it. Maybe I should replace the engine with a jet iengine. I bet they don't have cavitation problems.

 

I'm still not convinced about the 'vibration-causing-cavitation' theory.

Mopartom

 

Mopartom,

Not wanting to sound rude, but believe it. I worked on John Deere engines for 20+ years, have been around Cummins, Cats, among others, and cavitation affects them all. Coolant additives or conditioners of some kind are necessary in them all to prevent cavitation.

 

Sorry, I'll be more clear. I don't doubt it is a problem with diesels as people here say. I know what cavitation is, and I know at least one of the circumstances that causes it. I just haven't yet been convinced that vibration is another cause of cavitation. It could be my problem understanding it, so maybe someone could dumb it down a little for me.

A little more . . .

Little more . . .

Mopartom

 

This isn't a perfect description (so I hope nobody yells at me too badly)
When the engine is running the cylinder walls are expanding and contracting very quickly and the whole engine is moving. The coolant is fairly viscous (slow to move "at least relatively") so when the metal wall moves the liquid phase of water lags behind for a split second. In that time the wall moved but the water hasn't. This creates a local low pressure area. If it’s extreme enough the coolant can boil when the water catches up with the wall the pressure rises and the vapor bubble implode (cavitation).
Since the vapor point is a function of pressure and temperature the hotter the coolant the more likely, or more severe the cavitation. And the coolant that was against the hot wall just a second ago is going to be pretty hot.

Other theories I've heard of are:
"Air bubbles" starting at the water pump and then traveling into the engine and imploding. If the pump was causing the coolant to cavatate you'd have to replace the pump not the engine. And it wouldn't be #7 or 8 which is very far from the pump failing.

Cavatation can also be caused it water is at a high rate of speed and has to turn a sharp corner, like when a large valve is closing (I've stood on an 96" butterfly valve when it was closing against 100+ feet of water, now that’s some serious cavitation) but the coolant in our engines isn't going that fast and I've heard of damage to more then one spot on the engine. If it were caused by a poor piping design the damage should be very localized, and specific to that engine. From what I understand (which is always changing) this happens on almost every diesel engine at some level and it happens in more then one location. So it not likely to be a poor piping design.

I hope that helps, the explanation isn't perfect but its how I convinced myself the vibration theory was probably right.

 

Popping you knuckles is a form of cavitation.

Have you ever seen a prop on a boat motor that has suffered cavitation?

Both cases it is from a vacuum. You can also make diesel fuel cavitate in an injection pump if a vacuum is present.

http://www.arrowheadradiator.com/cav...ng_systems.htm
Cavitation is a weird phenomenon. Mostly its the really old 6.9s and the pre powerstroke 7.3s that need to worry about it. Ive run a diesel on the same coolant for 130k miles with no cavitation. At the time I was unaware that a problem could develop. That engine is still running fine.

 

A little factoid.

 

OK, here is my $.02 worth. Cavitation is not an issue in gas engines because the gas burns and, comparatively speaking, the pressure is fairly low. In the case of the diesel engine the fuel literally explodes when it is injected into the superheated air in the cylinder. The pressure pulse produced can cause some of the coolant on the other side of the cylinder wall to vaporize inducing the cavitation.

 

I read some of this forum a while ago and got scared of cavitation, so I went to my local pepboys and after looking through all the fuel and coolant additives and not seeing something that mentioned cavitation, I talked to the guy behind the counter, and he said that whatever stuff I have, it's fine if it's green. After reading this forum over, I see that he was wrong. Luckily it's a low mileage engine and I've only had it for a few thousand miles (but I have no idea if the guy i bought it from knew about cavitation).

I snooped around online for coolant filter/conditioner kits for a 6.9l, and i found evanscooling.com, which makes NPG and NPG+, which claim to be god's gift to cooling systems (transfer heat faster, last 500K, prevent cavitation, etc, etc...). Has anyone used this stuff?