everyone hates the thermos... i bought a supercheap 14" fan (biggest i could fit) and bolted it straight to the radiator bracket... 30 degree day, on sand, low range first gear revving at 4000-5000 rpm for about half an hour, and sat on a little over halfway for most of it. idle for about 5 minutes and was back to 1/4 on temp gauge.
IMO buy a quality fan though, dont do dodgy and cheap like me
BTW, i didnt do the upgrade to help cooling (my old fan was fine for that), i did it to be able to turn it off in water crossings after i snapped a blade on my old fan and put it through the radiator in deep water