Originally Posted by Fourn3833
most engines today run at about 200 degrees so teh fluid is no cooler than the radiator it runs thru
The thermostat is in the engine block and that opens to allow water to flow if the temp at the t-stat is at or above 195F. If it's cooler, as it would be when the engine is first started, then it's closed and the water does not flow to the radiator. It doesn't take long for things to heat up though, and the ideal sitiation has the engine block at 195F - for efficiency and for emmissions purposes.
Can't say I've measured the water in/out of a rad to know how much cooler it is at the bottom - 150? Cooler?. Temp sensors like you may have on your dash are in the engine block (usually in the head but not always) so they should stay constant if the t-stat is working properly. The fan will turn on when the 'natural' airflow isn't enough to keep things cool, and at highway speeds the fan usually won't run.
You'll notice it's constant in the 10F winter and while towing in 95F heat with the A/C on, so I'd imagine the rad can dump a lot of heat when it has to.
the proper routing of the trans cooler lines is trans to the cooler in the radiator then to the aux cooler and then back to the trans.