405 Diesel apparent overheating

Noticing whisps of steam from the air vents, I diagnosed Heater matrix
leak. Added a radiator weld additive, which seemed to cure immediate
problem temporarily. Changed the matrix, bled the system, run car to allow
fan to kick in 3 times and then idle for a few minutes. Allowed to cool,
opened cap, topped up to max level and took for 50 mile test drive. Once
cool, opened cap, everthing OK!. Drove for a week, approx 500 miles.
Checked coolant level when cold. Upto top of expansion vessel. Bled system
and continued to drive. Checked two days later level OK. So continue to
check levels on daily basis, with having to vent pressure from cap before
removing. With continued checks, noticed that eventually relieving through
radiator cap is evident whilst running. However, no indications from
gauges, smell or feel that engine is overheating. (This week stuck in
traffic for 2 1/2 hours with no signs of overheating. At the weekend,
after 8 hours from turning engine off, when checking fluid level, had to
release pressure (coolant cold!). Its got me baffled as the system seems
to be working OK. Pulled over the other day, let idle for 5-6 minutes,
cooling fan kicked in and didn't restart within the next 5 mins. No
evidence of oil in the water and no water in the oil. Head gasket
immediate thoughts, but why has the car not seized, or shown signs or
smeels associated with overheating. Any suggestions?

 

Hi Pugman,
I have had a very similar problem to this. It was found to be the head gasket
which was presurising the cooling system. In my case the coolant was being
forced out through the threads on the header tank screw top but no signs of
overheating or oil in water etc.

Regards
Dave G