is there anyway to test the thermosensor without removing it from the block? i was thinking of starting up the engine without the rad cap on, measuring the coolent temp while taking a reading before the fan relay to see when it would kick in.

 

I wouldn't leave the cap off while the engine was running. a 15 Lb cap raises the boiling temperature of a 50/50 mix antifreeze/water to somewhere around 235-250 Degrees Farenheit. Without it, It's signifigantly lower.

<Mr. Wizard>
The principle is that when something boils, the molecules begin to move around fast enough, ricochet off eachother, and eventually seperate from eachother. When the molecules seperate far enough and are moving fast engough, they become gas, in this case steam. Higher pressures keep the molecules together. This is why water boils at a lower temperature in the rockies... The low air pressure. Hence you'll see longer cooking times for high altitude locations.
</Mr. Wizard>

If I were you, I'd just watch the temp gauge. The fan should kick on and off at about halfway up. Alternatively, you can get an infrared gun type thermometer. They're a bit pricey. I think I've seen them for $50 at the cheapest, but I don't remember where. You point it at what you wanna measure and pull the trigger. Most of them have a laser sight for aiming.

If the fan doesn't kick on and off, pull the wires from the temp sensor and short them together. The fan should stay on... If it doesn't you've got electrical problems.