It maybe that the unsuitable fan is the problem ... designed for another vehicle with a bigger radiator possibly, so blocks too much of your rad ..... I have a standard rad and fitted a Davies-Craig electric fan to the front of it ((surplus off my racecar) ... just a manual switch on the dash and fitted in case of exceptional circumstances as others had reported overheating in traffic...have never had to use it in two years .... temp stays fine and stable whatever ... recently did a 1500 mile road trip via all types of roads and traffic, two-up and all camping gear and luggage for 2 weeks on board without a blip.
On here somewhere there's an interesting vid of someone who did an airflow test having tufted the bonnet and rad area ... there's a lot of air just never goes through the rad .... just bypasses it completely due to not being able to get away from the engine bay ... air needs an 'exit strategy' every bit as much as it needs an 'entry strategy'
K
