I'm Stumped...Coolant/Diesel Smell in Cab 2005 F-250

[Dawgman]

I have been trying several tunes to help get some better MPG's for my 6.0, and I'm currently using 8r20. In the last few days, I've noticed the smell of coolant/diesel coming through the vents, and can also smell it around the engine area after turning off the vehicle. There is no visible evidence of a leak on the ground, or on the motor. Also did a trouble code check....None.

After setting it back to the original back-up, I took it to a local diesel shop, and the mechanic checked everything out, we went for a test drive, and guess what?? No smell...So, I'm stumped.

Thoughts?

Ford F-250 6.0
Cal ID VXCF4D3
U7165 crom 8r20
128,500 Miles

[mikel]

Not uncommon for a 6.0 to be losing coolant in any number of places...