Three weeks ago, I'm on my way to work. Mileage to work is 15 miles one way, about 20 minutes travel time and the OAT was 68°. 120,000 miles on the clock. Initially, after about 3 miles, I noticed no heat to get the fog off the windshield. Temp guage was moving but not like normal. Figured it was a heating system problem. Got about half way to work and the fan goes roaring. Looked at temp guage and it was not normal and was below where it normally is. Guage never got to normal operating temp. Had 4 stop lights to contend with and the fan is still roaring with no overheat condition indicated. When I got to work, I raised the hood and I could feel the heat. Saw a small amount of fluid on the ground. Looked under the front and the lower radiator hose was completely off. WOW! No coolant in the radiator or about half the motor. I thought the motor was toast. Let it cool down for 4 hours and filled with water. Started right up. Sounded normal. Drove home and everything was normal. Well, almost everything. About 5 years ago I studded the motor but did not change HGs and I had a slight puking issue before I studded the motor. All was good for about a year then I had a slight puking issue show up. As long as I did not stand on it and kept the coolant just so I could see it in the tank, when cold, it would not puke. Plus I would see a constant 20 lbs radiator pressure, even after the motor set overnight. So I had a slight HG leak that was manageable.
After running the motor hot, I no longer have a HG leak. The high engine temperature, experienced during that trip, finally sealed the HGs. No more puking, the radiator pressure lowers to zero overnight and my EGT is about 150° lower than normal. The motor runs great. My big concern was did I fry the FI seals. No indications yet.
I attribute the motor surviving and not coming apart to 5 things: it was a cool morning, the fan did what it was suppose to do, no sustained high speed driving (above 60 MPH), 14.5 quarts of Royal Purple 20W-50 synthetic oil and 1 quart of Archoil 9100 friction modifier. The transmission did not suffer any damage as it has 22 quarts of Royal Purple synthetic ATF (+4.5 quart deep pan) and 35 ozs. of 9100 friction modifier.
The motor will officially melt and distruct at 350 degrees. If you stay below that they may survive. I wouldn't test that theory to many times though.
That was the wierd thing. When the lower hose comes off a lot of coolant drains. I assume about half. With what coolant that was left in the motor, I thought it would make steam and send the temp guage out of sight. Niether the water or tranny temp guages went full max. In fact they never reached operating temp during the whole trip.