peugeot 205 diesel overheating at speed

I have a peugeot 205 diesel, It only overheats (red temperature light
comes on) when I am in fifth gear and driving over 70 miles an hour or
when I am in fifth gear and driving up a hill where I need to have the
accelerator peddle pressed to the floor to keep the speed at 60. The
coolant is clear, not muddy coloured and I have recently bled the
system of air. The engine is not using water either, the water level in
the expansion tank remains relatively constant. The car never overheats
when sitting in traffic. How can I fix this and stop the car from
overheating.

 

It sounds like it’s blocked up somewhere - probably the radiator.
If it was the thermostat sticking then it would over heat in traffic
too.

Try flushing it out with that rad stuff and then use a hose pipe in
the rad to flush the bits out.
Simply draining it then filling up will not clear a blokage.

And

 

wrote in @q16g2000cwq.googlegroups.com:

seized brake calipers?

 

The brake calipers have been siezed but I was able to work them free
without having to replace the sliders. Is the engine overheating a
common fault associated with siezed brake callipers? Should i be
replacing the sliders, since they have seized in the past?