I went to start my 2018 Disco with 67k miles and found my coolant tank empty with the alert on the dashboard. When I attempted to start the truck, it struggled to start, and when it shutoff I heard hissing coming from the exhaust coupling right behind the transfer box. Any idea for why there would be pressure building up in the exhaust system to cause it to continually let off air pressure through a coupling for at least 2-3 minutes after a failed start?

I am posting two videos, one of the attempted start, and the second of the exhaust coupling hissing while the truck is not on.

Thanks for any ideas.

 

What engine? What are the codes?

 

It is the V6 gasoline engine. I have a Bluetooth BlueDriver code reader that I used to use on my older jeep, I just plugged it in and it did not pull any codes. I am not sure if this code reader is compatible.

 

No ideas about the exhaust hissing but if you lost your coolant you might want to check your crossover pipes for leakage.
Have you had those plastic parts replaced yet? Known to fail at your mileage and can cause catastrophic overheating that the temperature gauge can't monitor (because the temperature sensor is on the section that doesn't have coolant in it when the crossover pipe fails).
You may not see the leaked coolant as it can pond on top of the engine below the supercharger.
You could try to see if it;s wet there by using a small piece of paper on the end of long skinny flexible wire pushed down below the supercharger.
Alternatively, you might see the coolant on top of the skid plate.

 

None of those parts have been replaced. I am going to research it and take a look at it in the morning and post back. Thank you for the advice.

 

Mine was leaking enough to empty the overflow tank repeatedly and I couldn't find any drips on the garage floor.
One day I was loading the cargo area while parked on a steep incline and found red coolant drips on the pavement below the skid plate
After removing the skid plate I could see places where coolant had sprayed.
My crossover pipes have now been replaced with aluminum aftermarket and LR parts.

 

Who did you have do the replacement work? I just watched a YouTube video by Lucky8 and saw their full aluminum replacement kit online for $440. Is this similiar to what you did?

 

I posted the parts list if you can please search this forum. I had mine done by an independent shop in Denver.
Included some crossover pipes, outlet pipes, thermostat and housing, some hoses, and supercharger and other belt while they were at it.

 

I found it:
This is for a 2017 Si6

Besides gaskets, the original repair used:
011038 Water Outlet Plug
049990 Tube, Thermostat to Engine
033994 Tube, Water Pump to Thermostat
045239 Throttle Body Heater Hose
The above parts are Genuine LR
090630 Tube, Coolant to Upper Hose
092992 Coolant Outlet Pipe
117568 Thermostat Assembly with sensor
122710 Crossover Manifold Rear
The above 4 parts were Metal by Euro Amp brand

The failed parts were:
090630 Tube, Coolant to Upper Hose
092992 Coolant Outlet Pipe

And were replaced with genuine LR parts which weren't available at first repair:
186859 Tube, Coolant to Upper Hose
186917 Coolant Outlet Pipe

The following 2 metal Euro Amp parts were not available in metal from LR and were not leaking after the repair so were not replaced during second repair:
117568 Thermostat Assembly with sensor
122710 Crossover Manifold Rear

Note:
When using aftermarket metal parts, the genuine LR O-rings were used. Don't use the O-rings that come with the aftermarket parts.

 

As others have said, crossover pipes are a common culprit. If it was them, never a better time to fail than with the car off.

With cold temps across the country, also wanted to ask if you had the proper coolant/water mix and didn’t burst a plastic coolant line somewhere with freezing water