I have a cooling issue as well on my 511 with filled block. If I use a flex fan and shroud, it cools fine in the driveway and driving down the road. When I installed the twin spal 12" fans(1100cfm/ea) with an aluminum enclosed shroud, it would cool in the driveway fine, but out on the road would run 218* in the heat. I have since installed 12" spal paddle fans(1600cfm/ea) hoping to pull more air thru the radiator. I think these enclosed aluminum shrouds like yours and mine don't allow enough air flow. My shroud has free flow holes in it as well. Waiting for the summer heat to see how it does. Again, when I reinstall the flex fan and shroud it over cools, so there is an issue with that enclosed shroud or maybe you need a bigger better fan. Look at A1 Electric, they have a nice spec chart of all the spal fans they sell. Hope this helps.