overheating after stopping 10 min

testing a friend's Disco - 300 TDi

coolant level checked, drove the truck for more than 1 hour with no problem: temp gauge stays at mid position, cabin heating functions

stop the engine for 10-15 minutes, after restarting the temp gauge moves towards the red line, no more cabin heating, slightly undoing the two bungs expells lot of vapor

wait a bit, feed it 1.5 liter to drink and all OK again (until next calling point that is)

radiator and thermostat were changed last month for new units, no bubbling in the tank with engine running ... any idea ?

edit: don't know why, call it feminine intuition, but my suspect is the thermostat, I'll try to get another one to test (can't try with mine as I lended my disco so the friend goes to work)

thermostat?

water pump?

core plug?

head gasket?

just took out the water pump, seems fair and recently changed I suppose (nice shiny long nuts)

a core plug would leak somehow I guess, so there would be rusty traces and I see none

not sure about 300tdi but theres quite a few core plugs on the 200 block and not all can be seen easily.

one at very back of block is quite prone iirc so worth a look there is also one behind the timing case but this is a lot harder to get to. If you're having to top up the water each time then its either air lock or losing it somewhere. Wouldnt really think thermostat unless you can see leaks.

Have you checked all coolant hoses are tight and not leaking? did you bleed it properly (fill through expansion tank, radiator bung and bung near thermostat)?

have you checked for oil in water? if so then head gasket is the possibility.

could be one of lots of reasons so worth starting at the easy (hoses/bleeding) and work your way down (gasket).

check the expansion tank cap for leaking, swap it for another.
also check the vent pipe from stat housing to 3 way connector, to rad top, and header tank. this can be prone to sludging up an wont allow air in system to vent from stat housing.
fill and bleed using correct procedure

just finished re-fitting everything now going to carefully bleed the circuit and check every hose and jubilee clip before I take it for a drive around

@nrgserv: I wondered what was "inside" that 3 way valve, before filling the coolant I'l have a look inside those small venting hoses

result probably tomorrow as I am truly tired of this one today !!!

Have you tried the p gasket

I think the prize goes to nrgserv !!!

the 3 way gizmo was blocked by something I would describe as looking like the fibers left by a scotch-brite scrub sponge when it wears away

the stat housing itself was (seemed) clean but I found the same material on top of the housing in the recess where the vent tube initiates

some road test and if OK I'll flush the complete coolant system as these fibers might be elsewhere and later clog the radiator or the engine waterways

edit: a friend said he already saw that and it might be the leftovers from some "magical" product supposed to cure radiator leaks ?

still working ok?

so far, yes, the guy took it back and already drove 300km
I told him to check the coolant level every day for a week or two, he said the first morning there was some air below the top bung so he poured a cup, nothing this morning ...