[patrickt]

Here's another small observation which probably doesn't help but I'll make it anyway. If I forget to close off my heater control valve, that sits on the top of the intake manifold and controls coolant flow to the heater core, then in the summertime the engine runs slightly warmer than if I remember to close it off. The coolant that is routed out the intake manifold, through the heater core, and then back to the suction side of the water pump never gets routed through to the radiator so it's already kind of hot. Now, that's not your problem, I just thought I'd mention it. And I know you didn't block off your bypass hose between the top of the water pump and the intake manifold or you would have said that, so that's not your problem. Maybe you have a whopper of an air bubble, but I doubt it. I think it's either engine related or air flow related, that's a WAG.