Ford Bantam 1.3 Rocam weird overheating problem

Hi All, new to this forum, but this is now where I am forced to try and get
some guidance on the issue I have. My Bantam has now stated with this
weird overheating problem about 3 months ago. I would not call myself
technically disabled but this issue has really confused me. In OCT 2019 I
had to replace the water pump as the bearings was shot. After that drove the
car with no issues. Then in May 2020 had to replace the thermostat housing
as it was starting to from the flanges. So that was then replaced. Again drove
the car and all was normal, but then as I said  this year FEB the issue
started. What is now happening is that if you drive the car in town everything
seems honkey dory. As soon as you drive on an open road for a short while
and then return to drive and stop conditions then the fan kicks in indicating
the car is hot. This seemed strange to me as it never used to do it. Here is
the confusing part. The time the fan kicks in , one can feel that the waterpipe
going into the radiator is very hot, the pipe exiting the radiator ( bottom one )
is cold. The radiator itself is also nice and cold.... SOOO, then I changed the
thermostat again, thinking I might have bought a bogus part. Problem
persisted. Then I thought to replace the CTS and still no joy. So in total now I
have replaced the thermostat twice, the CTS twice It does not loose any
coolant. The level stays constant so there is no leaks in the system. Then I
took  it to check if possible head gasket or cracked head. The guy then
checked and said everything is OK. He then suggested we remove those
restrictors from the 2 small pies connecting to the water bottle, because
according to him, this could be blocked. Once removed we checked it and
they were not blocked. Nevertheless we left it removed. I then drove the car
for about 3 weeks and it seemed OK then. Recently I decided to put those
restrictors back because now the morning warm up time takes a lot longer to
reach normal operating temp. Then as soon I fit them back - the issue is
back again. This really confuses me why a car can drive for 12 years with
those restrictors and all of a sudden is now causes overheating ( OK I have
to say the overheating condition only caused the needle to go 3 quarters ). I
like to keep things original so according to me those restrictors should be in
the system regardless and the car should NOT overheat. I have also flushed
the radiator during this fault finding time. And I have always kept my coolants
ferly  clean. I am now at a point where I am tiptoeing between replacing the
water pump again or the radiator but I really don't ant to spend unnecessary
money playing the guessing game. Sorry for the long description but I
thought it good to give as much detail from start. Anyone got some advise on
this?