The fan seems to be working fine and the belts are in good condition. Not change the temp sensor but could be worth a go. The stable running temp is the bar below the 100 mark. (not sure exactly what this is) the spike saw the needle shot round probably 85-90% of the way so i pulled over. before changing the water pump and thermostat the other day the warning light came on.
tested 1 bar for approx 1 min/90 secs, there was a slight drop initially then it maintained a reading just below 1 bar. Fairly confident there are no leaks.
I didn't leave the engine running for long enough really to see what the temp gauge did, it got hot so i pulled over for fear of warping/cracking heads etc.
After doing the thermostat there was more movement in the temp gauge, got up to temp then it dropped after around 2-2.5 miles then the heater got warm. i'm told this is normal!?
when i had mine the temperature always sat around the 100 mark with slight fluctuations. The needle did rise to 105 but not into the red. the numbers refer to the temperature.
the pressure test you conducted had the results i'd expect with it initially dropping then staying stable which indicates a sealed system.
with the temperature getting up to temp then dropping after a short period of time is perfectly normal as its a indication of the thermostat working as intended.
when a the temperature rises and people panic they switch the engine off to save it........with the engine off how does it then cool down as there is now no air flow through the radiator and the block then goes into a heatsoak mode slowly cooking itself.
sit with the engine at a fast idle 1,000-1,200rpm as this runs the fan faster thus pulling more air through the radiator improving the cooling of the coolant and block. could be a hard choice to make which is why the electric fans are slightly better as you can have a manual overide to keep them running at a faster speed
