Sounds like an air lock problem. I would be tempted tp park the car on a incline with the front of the car being as high as possile, top up the water bottle and squeeze all the main hoses with the ignitition off. Check the water level again and see if it dropped, start the engine and slowly bring up to running temp. then change all the temp setting on the heater controls to full, minute later back to cold, minute later back to hot and then check the water level, if you feel confident to squeeze and check the 2 main rad hoses for heat and squeeze them a few times to release air.
(BE VERY AWARE OF ALL MOVING PARTS UNDER THE BONNET -
IF YOU ARE UNSURE OF WHAT YOU ARE DOING AT THIS POINT
THEN DONT DO IT - SAFETY 1st EVERY TIME)
This can be done with the expansion bottle cap off while you are checking for air locks, Do not rev the engine as I may cause hot water to gush out of the header tank/expansion bottle. If there has been an air lock, top up lost water to correct level, refit the cap and take for a spin, open and close the heater controls at different speeds, when the car is parked allow the water /coolent to cool before retopping/checking and taking off the header tank cap.
Allways keep an eye open for oil in the water.
Other causes are the rad fan themostat switches for the fans, one of which you have changed.
Blocked radiator, what cooler/state was/is the coolant in.
Is heat emmiting from the heater matris into the is=nside of the car oh, possible/partially blocked heater matrix if not.
Please be carefull through testing of moving parts and hot fluids.
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Topic: car overheating at speed (Read 948 times)