I'm an experienced tech. 40 years of building and working on domestic and foreign cars.

I have a one owner 2016 LR4 that I bought with 100k miles on it. I have all the service records. It was well taken care of.

It had a full cooling system refresh... water pump, all hoses, front and rear hard lines, etc done 5k miles ago. Also had front suspension refresh and all the other known ailments taken care of.

I did spark plugs, air filters and oil change three days ago.

This morning my wife got a low coolant notification. I looked and the expansion tank was empty. So I filled it. Ran it. Watched it with the cap off to see if any bubbles or if it immediately empties, etc... seemed good. Then I pressure tested the system for four hours. Held pressure.

Wife took it to work which is a 45 minute drive. I went to check it there and level in expansion tank was where I filled it earlier.

I also used UV light and could not see any coolant leaks.

So..... maybe a bad bleed and an air bubble worked it's way through? A leak somewhere when system not under pressure?

Is there a place these will leak that I won't be able to detect with a uv light?

Did I jostle something during the plug change maybe?

 

probabaly an air bublle in the system somewhere. Last time you fiflled it did you go through the painstaiking factory bleed sequence. I always just vacuum fill these LR4s as there are many stories of air trapped in the systems. Also if you have the rear heat/air, some have reported leaks back at the spare tire area where you might not notice. Finally, I would carefully check the V. Especially if the front crossover was not JLR oem pipes when renewed. rear heat manifold sometimes leaks as well and coolant doesnt make it to the ground. burns off around the trans, exhaust, lingers on the skid plates etc...

 

I have never serviced the cooling system on this yet. I would hope the tech who replaced the water pump and hard lines did the correct procedure. But, who knows. I do know all parts are JLR.

If I don't get any more loss I'll chalk it up to an air bubble. If I do then I need to start digging.

 

Found it. Thermostat seeping at the seam. So I'll be replacing that along with any compromised hoses I find.

 

thermostat housing is a 2 part deal; I would order both pieces as they typically stick together and become brittle. the lower piece can crack when taking them apart.

 

Yeah. I ordered the thermostat and hose.

Now it stopped seeping at the thermostat though. lol

Not sure what caused it to seal back together.

I'll replace it anyway because I'm worried it will just blow apart now.

 

These're notorious for leaking, even just slightly, at any point they can. Also never have had good success with bleed filling these circuits, always use a vacuum lift shop air system for perfect fills, too many places to get air trapped somewhere any other method.

 

Yeah. I've seen they are and I have a vacuum fill system. So I'll be good.

 

Took me all of 30 minutes to remove the thermostat. It came off the bottom hose fairly easy.
The rubber seal in the bottom hose is still fat and rounded in the connector. So I'm wondering if i should even bother replacing it.

Heres a couple pics of the old thermostat at where it was leaking at the seam. Compared to the seam on the new one.





Also it really helps to have this hose clamp tool. Saves you lots of time than fiddling with channel locks.

 

Spent an hour today putting the new thermostat in and vacuum filling. Easy peasy. Vacuum filling is the bomb! Zero issues. Don't know how I never saw that before but it saves so much time.

Had so much time left over she got polished after the job.