[Bob S]

Dave,
You asked about temperature differential between radiator inlet and outlet. Here is a long answer to your question. I did a bunch of testing of that awhile back and concluded that due to other variables it doesn't mean much. For example: With a thermostat that is just partially open, flow rate will be quite low. In that situation, since the water is moving slowly, its temperature will increase a lot while flowing through the engine, and will likewise drop a lot while flowing through the radiator because it's in there for a relatively long time. With an open thermostat (or none) water flow is fast, so there is less time for gaining or losing heat. The temperature differential through the engine and through the radiator will be much less. That doesn't mean that less heat is being transferred. The total BTUs being being dissipated by the radiator may be about the same. If each gallon flowing through the radiator gives up just half as much heat, but there are twice as many gallons flowing through, the total amount of heat being dissipated will be about the same. With warm air, high flow rate, and low engine load (not much heat being generated), the temp differential might be as little as 5 degrees. With cool air, low flow rate, high load, the temp differential can be many many times greater. All this is not to say that there is no point in measuring those temperatures. Just keep in mind the other variables and that there is no single "should be" temperature differential.

Bob