My conclusion was heat soak. After many temp readings from temp gun I determined the best place for a temp sensing unit is NOT the rear passenger head. Put it in the intake by the thermostat housing and runs steady 190-200. Pete

You've highlighted something here.

What alot of people don't know is that your cooling jacket is set up as a "manifold system" just like one of those roll out perferated hose lawn sprinkler systems. HOw it works....and what that means if you have ever observed one of these....they have strong flow at the source (next to the hose inlet) and very weak flow at the end (fartherest from the source).

This analogy is perfect for understanding the cooling manifold function. At points near the front of the engine and thus water pump....strong flow and pressure. As you move away from the source and at the far back reaches of the manifold the flow is diminished just like the lawn sprinker! Because coolant flow is paramount in removing BTUs....the rear cylinders will always be hotter than the front (unless compensated for) and the rear bung sensing location will always read higher coolant temps than anywhere else in the system. Think about it!

With the advent of the modern aftermarket water pumps that are high volume...this usually aleviates some, most if not all this differentiation between the front and the back. Or course...you see round trackers drill, tap and connect directly to the front waterpump from the rear of the heads all the time to compensate for this physics lesson fact as well.