When you check for pits / holes in the ports of the cyl heads, will you do this under pressure?

sl

The head I had go bad was pretty obvious. It had coolant dripping out of the intake port at #4. On close examination of the port I could see the droplets forming inside. It passed a crack check. That leaves porosity pretty much the only culprit remaining.

Normally a shop uses a device that possitions rubber blocks over holes, to block all the head/block passages, plugs off all but one water opening, fills the head with water and puts air pressure to it through the open port. I don't recall how much pressure they use, I believe it was only 30 psi or so. If the casting is porous it will start to sweat.

Automotive machinists are generally equipped to do this test, though you might have to hunt around for one that will handle a head as heavy as these.

Unfortunately, I have heard of no cure for porosity so we'll keep fingers crossed and hope it's something fixable.

At the dealer I made up a simple testing setup with an air regulator and I found dozens of problems using it. I just blocked off the cap so no pressure got through it unless it was a good pressure cap to hold the 15 lbs. and then hooked into the cooling system wherever was convenient and I never went higher that 15 lbs. pressure and then when I got the pressure up there would cut the supply off and observe the leak down and start looking and usually it didn,t take long to find the trouble.

The 3 cyl ford diesel (and maybe the gas) engines are known for this problem as well. I think those in the know call it 'cavatation'. It shows up in their product at the water jacket in the cly wall. The dealer carries an additive to add to the coolant to prevent this...

also, I tested a set of marine exhaust manifolds by capping off the coolant openings and pressurized them w/compressed air (about 30 lbs) while I had them submerged in water....sl

A D7E operator around here ran the same machine for many years and well over 20,000 hours. He always with out fail let the engine tick over at low idle for 15 minuits before shutdown. The aim was to get the engine as cool as possible before stopping, this was his theory on stopping heads cracking it seemed to work for him. I would have thought the thermostat would have closed to keep the temp up to spec.
my 2 cents wimmera farmer

Cavitation is a problem on most Diesels, but the only place where I have ever heard/seen of it happening is on the outside of liners. The use of a coolant conditioner added to the coolant, or a coolant conditioning filter, or long life DIESEL engine coolant will prevent cavitation. John Deere has a long life coolant that does not require changing for 5 years or 5000 hours (IIRC). Cavitation is caused by tiny air bubbles eroding the metal.
The pitting on his cylinder head is from water setting on top of the piston. I imagine if the pitting was deep enough, it would weaken the material enough where, at some point, either rusting from the inside, or compression and flame erosion would penetrate all the way through, allowing coolant to enter the combustion chamber.

very well explained! thank you...sl

The D7 head that developed porosity for me was cracked before I got the machine. I had both heads welded. One worked out fine. The other was porous after the welding.

Cast iron is unique stuff. It is iron, of course, with graphite interspersed throughout. The graphite is not alloyed with the iron as with carbon steel, but exists as carbon particles. When the iron is heated too hot for too long, the graphite can be burned out of the iron and the casting loses a lot of it's desirable charistics, among them the ability to hold water.

By same token, hot iron cooled in water quickly removes the carbon from uniform dispersion in the iron and the result is "chilled" or "white" cast which is brittle as glass and hard as a whore's heart. it was used for years in plow bottoms and they would wear forever.

Quick and not the best course in metalurgy, it is the best I can do without going back to my old text books. Hope I have helped you get a rough idea of the problems associated with heating/cooling cast.

My understanding of "cavitation" is the formation of bubbles in a liquid medium that form and collapse with the resulting "shock wave" causing the metal displacement (erosion)......same effect with water forming steam in the combustion chamber.

It,s unbelieveable how it can damage things and I,ve seen liners that were eat away almost through the inside wall. The Cat preventive to put in your cooling system is for a pint 8T1589 and a qt. size is 3P2044. They also show a 1/2 pint size and is 6V3542