Auto fan randomly working in 379 with Detroit 60

Try a new fan switch solenoid. They tend to act up a little before they fail. When they fail your fan will be stuck on.

 

Mine did..until it didn’t. Lol, I hit the manual switch and that’s when it decided it didn’t want to shut off anymore. Mine acted up about two days before it completely failed.

New solenoid should be somewhat inexpensive. Had mine replaced at Kenworth and it was $150.00 parts and labor.

 

I'm not sure on a Detroit but on a cat the fan comes on for engine water temp at 217 degrees. Not any sooner, at least for water temp. So are you surenits getting warm enough to kick the fan on? Factory temp gauges in Pete's are notorious for being inaccurate

 

On my Kenworth it was located on the firewall, left side. I’m sure if you go pick one up they can tell you where it’s located.

 

Again I'm not familiar with a Detroit but a cat has one sensor for the gauge and another for the ecm. Possible sensor for fan control one ecm isn't reading correctly or bad connection in harness.