I don't understand........this has happened twice to me. The upper hose is somehow blowing itself off the fitting, in tact with clamps still on. Result of course in total loss of coolant. The first time this happened to me a few months ago (maybe a year) , I eventually discovered a bad water pump "weep" hole that was allowing coolant leak after I replaced the thermostat and reconnedted eveything. Changed the water pump and been driving fine since. Yesterday, got the engine overheating message again, puled over, shut it down and inspected to find that upper hose completely off the fitting again. ???? huh?? It's as if someone is sneaking into my locked garage and slipping the hose off if I didn't know better. What kind of pressure is there in that upper hose that would cause it to blow itself off there with seemingly tight stainless steel double clamps????
BTW, there is no other evidence of coolant leak anywhere .

 

ps... this is 2009 xf 4.2

 

Lots of hoses can you post a picture of what actually came off?
.
.
.

 

The actual upper radiator hose to tstat inlet

 

Thanks for the picture. Any chance you have abnormal pressure in the cooling system?
I would for sure try a new hose at first. I have had several "problem" hoses in the past that just would not cooperate.
No matter what I did.

Can you pressure test the system while the engine is cold? Might give a clue to what's happening as it's a rare problem?
.
.
.

 

Two years ago, when I installed new hoses, and installed fresh coolant in our former XF, I had the same thing happen. Fortunately, I was on a "test ride", and only a block from home, so I dashed in the driveway, and shut it right down. This had me think, as I was pretty sure that had I not gotten the clamp on properly, in the first place, it would have blown off right away. But this happened after the car had been running for about 10 minutes.

That got me scratching my head, wondering what had happened, and initially beating myself up, thinking that I foolishly had not installed the clamp correctly. But it appears that it also happened to you......strange, to say the least.

 

It's happened to me twice now on this car. And I know how to clamp a hose. I have boats and clamping hoses is life or death. It's really weird because the hose is like new. And there isn't a lot of room in there for it to back completely off by itself. It takes effort to push it off that fitting with the clamps loose. I am perplexed. So now I have added coolant after reattaching the hose and going thru the bleed process. There are no other leaks and the car starts right up and sounds good, oil looks good. But I really don't trust this vehicle whatsoever. It has now become an "extra" car, parked in the garage to only be used if emergency.
How in the heck is that hose coming off?

 

I know it's somewhat of a "long shot", but possibly the neck of the radiator got wet and "slimy" from some previously undetected seepage, which made it slippery, and a pressure surge caused the hose to slip off?? I could see that possibly happening, with the OE spring style of clamp, but with the band clamp(s) that you have now, I don't see it happening. Let me ask this, when you re-installed the hose, did you wipe the radiator's neck thoroughly, and maybe the first inch or two, of the inside of the hose, to make sure any trace of coolant, which is slippery, was gone?

 

Should not cause that because I use and have seen instructions for hose installation recommending that coolant be used as a lubricant to aid in installing the hose?
I also regularly use silicone grease to help with tight small hoses and have not had them blow off either?
Still a mystery and certainly not reported?

Any chance you can measure the coolant pressure? That way you can cold test the hose to see if it will hold under pressure?
Maybe the cap is holding too much pressure?
Of course that's weird too and usually they fail in the other direction.
.
.
.

 

Actually I don't know how, or have tool to measure coolant pressure. But it is so weird to happen twice, about a year apart. Honestly, I am baffled by how that hose can come off on its own twice. Removing that hose deliberately for any kind of service is or can be a physical effort. I question if I am sleepwalking and going out there in the night and sabotaging my own car. Yes, I would expect to see some other coolant leak somewhere or a bulging hose, but nothing.......The ONLY thing I can think of to ask is if the heater or dccv is somehow malfunctioning and causing excessive pressure in the system? The first time this happened I vaguely remember that my wife said she was having trouble getting the air conditioner set at her desired temp and was randomly pushing and adjusting climate control settings shortly before the hose came off. Also, what if the tstat did not open? I know that should cause an engine overtemp condition, but it the tstat remained closed, would it inhibit upper hose flow to the point that the hose decided to relieve itself by blowing itself off the fitting?

 

guys, I wanna go back to this. So I have reinstalled the upper hose which I believe is the coolant "in" to engine line. and I have mostly bled the system. I have not yet measured engine temp with obd but I notice that when I let the engine warm with the climate control on full hot max fan, the outlet hose out of tstat housing or "outlet pipe" remains cold to the touch. Logic tells me this indicates the tstat is not open and therefore that outlet side would remain cold. If that was the case, would that cause the upper hose to pull itself off the upper radiator fitting as has happened recently? I do have hot air from the inside vents

 

For the price of a stat, I would definitely change it and see how it goes. It's a fairly easy job if I recall from my last 4.2 XJR.

 

I would be looking at the coolant fill cap. That cap has 2 operations one to release pressure when hot and the other to release the vacuum pressure when the engine cools down. That operation allows the coolant to flow to and from the coolant reservoir when needed when the engine heats and cools. h