Cooling issue? Please help. 12.7 detroit 60

bad sensor that's what it sounds to me if it's doing it periodically

 

Check codes, if low coolant code is stored, check wire to coolant sensor. Fan kicks on, and blows wire around at the plug. Making it an intermittent problem. Pyrometer? No idea.

 

I got a 14 liter detroit doing exact same thing. Hopefully we can figure it out.

 

Do you have a boost gauge?
And if you do what are the boost readings when you get fluctuating pyro readings?

 

That doesn’t sound like a boost gauge at all.
Is that a vacuum restriction gauge for your air filter?
Maybe post some pictures of the gauges of what they read would be helpful?

 

Yeah that’s air filter restriction gauge. You didn’t say what year Truck is. You should be able to turn key on and push in override button, count yellow flashe, then red flashes 2 digits codes each. 4 flashes, followed by 3 , for instance, yellow are stored (old) codes, red flashes are active codes, get the codes. Probably just a broken wire or a Loose pigtail plug, When the fan goes on watch and see which wires to which sensor gets blown around. After you fix it zip tie up good, So the wiring doesn’t move.

 

I'm thinking engine temp sensor, or thermostats, or gauges, or bad grounds?