The high pressure line is a high pressure hydraulic line. The can leak from the attachments to the fittings. The will leak where the line is damaged Or if it as a very old line they can crack.
Your heater core has a leak, have the station pressure test your cooling system if it does not hold pressure you a leak in system
The problem is a leak inside the high pressure oil system. When it is hot the leak expands and causes the truck to not start.
The guage goes up when the vehicle is overheating. Possibilities to start checking are: air pocket in cooling system, sending unit is defective, cooling fan not working, guage is broken, head gasket leak, cooling system leak.
Pressure testr the cooling system and obseerve where leak originates
Pressure test system and watch for leak
pressure test the cooling system
because the leak releases pressure?
A coolant pressure test is used to detect a leak on the coolant system.
You would have a leak in the coolant system somewhere and you need to have the system pressure checked.............
If you do not visibly see a coolant leak, have the cooling system pressure tested. If the leak is not obvious it could be internal.
Have cooling system pressure tested to determine origination of leak