I hope you're right. I have a ford in the driveway that runs great but I cant keep water in it due to a small leak on one head. I acts much like you describe. A very small leak would not necessarily have any noticeable effect on the way it runs. It could however make a bubble that could interfere with circulation causing it to overheat at hwy speeds and blow water out. Even an inadequate radiator should work better with a 50 MPH wind blowing through it, shroud or no shroud. My CJ came with a 3 core rad and a 160 degree thermostat. It wouldn't make enough heat for the heater to work. When I destroyed it by punching the fan into it (another story) I replaced it with a 2 core and put in a 180 degree thermostat. I can Idle around all day in 90 degree weather without overheating. If I speed up at all it goes immediately from 190 down to 180 or less, At 60 MPH it cools right down to 160. (manual gauge with bulb in manifold) I have a six blade flex fan and no shroud. BTW, whatÆs the deal with the Mexican 4.6? Is it like a stroked 258 or something else?