When the engine is running, and the coolant level is correct, the water pump forces coolant into the cylinder head and all is fine.
When the coolant level is low, the water pump still forces coolant into the head (the thermostat is the main system restriction in most cases), and the coolant temperature may be fine, but as soon as the engine is shut down, the coolant runs to the bottom of the radiator and lower part of the engine crankcase.
If the coolant level is low enough, the bottom deck of the head no longer is covered with coolant, and the metal temperatures in the valve bridge and seat insert skyrocket.
The high temperatures in instances of hot shutdowns with low coolant levels cause massive thermal induced hoop stress on the valve seat insert. The hoop stresses can cause the insert to fail in compressive yield.
Essentially, the lack of coolant on shutdown causes the insert to shrink because of the thermal stress. When this happens, the press fit of the insert to the head base metal is lost, and the insert drops, usually on startup.
I don’t profess to know what material Kioti uses for their inserts, but there are different materials available with different cost / performance trade offs.
I went through this failure mode some thirty years ago when working on a similar valve drop issue for the Diesel engine manufacturer I worked for.
The issue never was on the radar screen until we had a rash of valve drops. There was a radiator quality issue at the same time.
We fought the valve drops for months, but couldn’t duplicate it in the lab until we devised a dyno test where we filled the coolant just shy of the deck, ran the engine till at normal operating temp, then did a hot shutdown. Bingo. The failure was immediate and 100% repeatable.
Running 100% antifreeze can probably lead to a similar failure. The silicates in some automotive grade antifreeze can drop out in the hot valve bridge drilled passage. If that bridge coolant passage then plugs with the silicate, and I have seen it happen when the assembly plant forgot to add water to the concentrated bulk antifreeze delivery, the bridge and valve seat temperature will increase, cracking the bridge, and possibly overheating the seat, resulting in a seat drop.
Sounds like a Mercedes diesel to me. I've seen a number of similar issues with their diesels in the 80's when content laws to keep America competitive with European and Asian manufactures dictated that a certain percentage of parts of a foreign manufacturer's auto HAD to be made in the U.S.
The first time, I had a Benz diesel overheat and it was loosing coolant. We could find NO active leaks, AND we spent hours trying to figure out why.
I finally found it was due to the rubber gasket between the radiator top /header, and the aluminum core! When the T-stat would open and the engine was at temp it would leak past the rubber O-ring type seal AND blow water past the seal over the engine. (We did not use coolant to test for leakage, because until we found the cause no sense to waste more money throwing away coolant. The radiator was NOT sealable and could NOT be repaired for any amount of money. BOTH headers were PLASTIC 'crimped' to the core. Man, what an abomination.
We got a brand new metal headers radiator and sent the very happy customer down the road. Every other shop for miles had tried to figure it out too. Guess I'm just persistent and lucky!:mur:
Second case was again something cooling system related on a turbo diesel Benz. This time it was failure to cool the cabin. After long struggle it turned AGAIN the crap part usages by Benz. The climate control box under the hood was subcontracted to Chrysler, (you know, bankrupt, then bailed at taxpayer's expense- who can figure out why?!)
Part was at least close to 3-400 dollars from the Benz dealers, IIRC. It would crack at the bottom section, which of course was some different material than the 'brain' section above, then the climate controls and it's massive number of hoses would loose vacuum and the whole climate control was rendered non-functional! Yippee. We ended up keeping one of the pricy units on the self. They were a sure sell part when we'd see big diesel Benzes roaring into our drive wanting instant cool between rounds of golf!:confused3:
Working on diesels I learned a lot about what they can and cannot tolerate. Extreme cold they essentially never get to 'normal' temp on the temp gauge. Extreme heat from a poorly installed block heater and loss of coolant, (as stated by me and numerous others here), will cause rapid failure, especially as Finn1 stated earlier.
Add one more factor to the equation: when too little coolant is being circulated through the cooling passages of the head it not only jumps to litteral 'warp' temp, it does so because an aluminum head on a cast iron block expands and contracts 5 times faster than steel. This means even if a head had a chance of surviving a blown out block heater from increased internal pressure built in the cooling passages, the engine HAS to dissipate the extreme overheat at the head, and something has to give since there is not enough coolant to blow off to the reservoir tank, as the system is designed to do under normal circumstances.
I strongly suspect the dealer and Kioti rep took one look at the engine and concluded the same thing I have. Owner installed block heater caused leaked coolant to point of no return. Block heater, weakest link; gave way when pressure built throughout engine resulting in cracked head, lost valve seats and blown out cause of the 'crime' failure of block heater - spit it on ground as evidence of bad install. Crime solved, case closed, next!
OH, and Kioti rightfully walked away... Seek recompense from block heater installer, NOT Kioti.
Sorry for long post but it's sometimes really difficult to get people to see reality, especially when most of the relevant facts are held back by the OP. English version- such is life!
