Engine overheats with no indication
 

My son has a newly acquired 2015 LR4 6 cyl. with 65,000 mi. that he has wanted forever it seems.
Yesterday while driving home the engine started to buck and shake. He pulled over and there was appeared to be steam coming from the engine compartment. He saw coolant sprayed over the engine in places. I asked if there was any warning and he said none at all the engine temp was normal and no warning lights. Its at the dealer he bought it from and it appears like a cylinder head gasket. The mechanic he talked to said that this can happen where the engine indeed overheats but there is no warning! He indicated that is one of the things he says that he really dislikes about these trucks. Is this true?
Any thoughts or suggestions greatly appreciated.
Tom

The mechanic worked on it for 7 hours he said and is almost positive it's the thermostat. It did overheat and at least one head gasket is blown.
They have a 2016 LR4 on the lot with 66K miles and they are going to put that engine, a V6 also, in his truck. Should take about 10-14 days they said.

So if the thermostat fails, in this case closed, will the temp gauge and warning not work?

Failed thermostat does not affect the engine coolant temp sensor. If a thermostat fails in the closed position, you would almost certainly see the temp gauge rise before any damage to the engine occurred, and certainly before the coolant system ruptures (the steam your son saw).

What you describe here is a common situation with these cars, but not due to thermostat failure. It’s due to failure of one of the plastic “crossover” coolant pipes (there is a two-piece pipe at the front, and a single piece pipe in the rear). The pipe ruptures and the system is suddenly without coolant at all. It most often ruptures in the valley of the engine, where you cannot see it, but coolant will typically flow out near the water pump. When the rear pipe ruptures (also cannot see it because of the location of the pipe), the coolant can dump onto the exhaust producing a lot of steam.

There have been many, many reports of this problem, and in most cases, no increase in temp was detected on the dash gauge. This is perhaps because the coolant temp sensors are designed to sense changes in the temperature of the liquid coolant, but once the coolant is gone, they are not so good at detecting hot air.

Before the new engine is put into the truck, make sure the coolant crossovers (both front and rear) have been replaced. At 66K miles, they probably were not done yet. If there is any doubt, just have them replaced. Then plan on doing it again at 120K.

Thank you very much for responding. The mechanic was pretty sure there was a blown head gasket. This issue seems to be due to poor engineering. The crossover coolant pipes are made of plastic perhaps as a casting would be much more difficult and expensive; I understand that, but why in the world is there not a reliable engine overheat warning system? Fortunately, this is all covered in the two month warrantee he has.
The new engine has 60K miles on it and I will be sure the crossover pipes will be replaced. The salesman/owner of the dealership told us they replaced a front and back part that tends to fail on the engine in the car which I now assume was the crossover pipes.
Yes, I have read posts here where the very same thing happened to others.

I’m sure there was a blown head gasket - that’s the first thing to go once it overheats. I just think it probably overheated from a burst crossover rather than t-stat failing closed. On that new engine, check to make sure they replaced both parts of the front crossover. It’s a 2-part pipe and it’s the part that goes into the block that fails. The supercharger needs to be pulled off in order to change that lower piece, so sometimes people will take a shortcut and just replace the upper half. That won’t cut it.

Good luck with it, and really great that the warranty covered it.