Temperature problem XK 150

The temp rises sharply when slowing down and the car blows out radiator water through the cap. It is fitted with an electric fan from Kenlowe (150 W motor) which is running ok. When traveling normal speed ( 40 plus km/h) there is no problem keeping the temperature normal. The thermostat is of correct type and opens around 78 deg C. The flow of water seems ok and I can´t detect any hotspots in the cylinder head. I measure temperatures between 105 and 110 deg C on the exhaust side of the head, the radiator cap is a 7 PSI cap. The carbs have been adjusted by an expert. The only part I have not mentioned is the radiator… it is the original and should have been rinsed at radiator company but … could the radiator be my problem?
I appreciates all ideas to solve the problem.

Is the fan pulling or pushing? There was recently a post in the e-type forum about someone receiving a new fan that was wired backwards.

The fan rotates correctly and pushing. I made the misstake to forget the fan when I went to negative earth! But the air flow seems weak for coming from a 150W fan.

Time to recore the radiator.
Modern cores are also cooling much better.
I recored the radiator’s of all my cars.

What is the typical cost of a recore?

Can we be sure what ‘pushing and pulling ‘ is being discussed/ agreed

A 150 rad cap should be 4 lbs.
If you have never had an engine overhaul the block will be full of rusty debris reducing movement of water.