Peugeot turbo diesel overheating on the highway Questions.

[Goce]

I want to ask for advice before a start disassembling and diagnosing it, probably someone has had to deal with this and can give me some advice many to avoid overlooking something simple, by my reckoning most likely is a stuck thermostat but could be a leak or a failed water pump.The car is 605 2.1turbo diesel (XUD 11 ATE) this engine combo has been in my family for the better part of couple hundred thousands kilometers and is never overheated, coolant has been changed regularly and is less than two years old. This morning on my way to work on the highway looked at my temp gauge and is at 95 degrees celsius it usually stays at 80 degrees, tried slowing down, then speeding up, manually turning the cooling fans on, it would not drop below 95, stopped at the first gas station bought some antifreeze but the expansion tank is full, and there is no pressure, got back on the highway it started climbing to 100 degrees and decided to turn the heater on full and the temp started to droop and with the windows down and the heater on full it stays at 85-90 degrees, the car had cooled down at work and was able to get out of the city by the time engine came to operating temperature and reaches 95 degrees then i switched the heater on full again, on straight it would hold 100 km/h without overheating on uphill anything over 7-80 km/h it will rise to 95 degrees, this engine it has the thermostat on the lower hose right at the water pump in a very tight place and i have to drain the entire system to gain access i even may have to remove the passenger axle, if someone has had similar experience even with a gasoline engine and has found out what was the problem please write, any advice is appreciated.

[Bean]

Is the rad getting hot?  I would check rad temps, and even rad hose temp post tstat to see if it's a stuck tstat - or if you maybe have a plugged rad? 

Rabin

[Goce]

The upper rad hose is warm and the top of the rad is warm, not to hot i can hold my hand on in for minute, the thermostat is on the bottom hose next to the passenger axle, had a look after i parked it, it has couple of drops not sure from where they came and are they coolant.

[SRDT]

The thermostat is not even on the hose, the thermostat housing is part of the huge external water pump.

If it was perfectly fine yesterday the rad is probably not plugged, too bad the thermostat wasn't stuck open.

If you don't like where the thermostat is located look a the XUD11BTE fitted on the 806, they put it on the usual place.

[Goce]

If it was stuck open i would just put the new style with the fuel filter on, but now i have to remove this one i may just replace it, in the meanwhile i removed the thermostat from the spare engine and tested it hot water and it started opening at 77 and was fully opened at 85 degrees, i'm thinking removing the old thermostat and testing it in hot water is my easiest way to know is the thermostat my problem.

[Goce]

Just wanted to update this thread in case someone has similar problems this can help, this morning i decided to start by removing the thermostat, to start my diagnosis, and as i pull it out everything was clear, the thermostat has failed apart, so no need to test it, the thermostat failed little crooked so was allowing little flow this explains the hot upper hose, in the picture you can see how the thermostat fails, and is the factory thermostat dated 92 and all the heat cycles made the metal fatigue.

[Goce]

New update on this thread, the replacement thermostat that was also from 92 failed this time opened. Basically the engine would never get over 70 C and i had almost no heat inside, so i bought a new one installed it and now is running as it should. Let's hope this thermostat lasts, its new. The inspection pit made changing it much easier, i also flashed the system and fill it with new coolant.