I need help on my 93 D250 LE with the 518 4 speed HD tranny. I am the second owner. The first owner gave me all the paperwork including the window sticker.He ordered it with the super-duty tranny oil cooler,which is located under the bed on the drivers side.It has a fan above the cooler,and a sensor where the fluid goes into the cooler.When the truck is running and I disconnect the connector and jump the connector the fan kicks on. My questions are
1. When is the fan suppose to kick on
2. Is there a way to test the sensor
3. Is ther a seperate fuse for the fan(I checked the fuse box,all is good)
4. what would cause it to go bad or not work- A year ago I have heard the fan kick on,so I know it use to work.
I just had the tranny rebuilt 30 miles ago,due to that massave spring in the O/D unit go bad and collapse. I do not want to drive it much till I fix this problem. Thanks for the help..........

 

Mine kicks on when the fluid temp gets to about 180. It goes to the small cooler by the radiator first and then thru the under bed cooler, usually runs cooler than that unless I'm towing up a hill. For reference, my water/tranny fluid cooler on the passenger side of the engine is no longer there. Was removed for the twins.I swear that the fluid runs cooler without that in the system. seemed to be adding temp from the water based on what I'm seeing now. downside is it takes forever to get the tranny temp up in cooler weather. My gauge sensor is in the pan and the temp is usually below 100 degrees until things get good and warmed up, then runs about 130.

I am thinking of running the fluid thru the under bed cooler first then up to the front cooler to see what that does.

 

If it is the fan/cooler set up that came from the factory it will come on at 210 degrees. Aftermarkets are set up to come on @ 180 degrees. Bypass it with a switch on the dash.