HEMTT Radiator Fan not Engaging

[dk8019]

Guys,

I think I may have an issue with my fan on the M977. I recall when I first got it, that the fan would kick on during normal operation, pulling a huge amount of air. I don't believe it is turning on now, and the coolant temperature has been working it's way up above 200F. Any thoughts, and which manual to start with for testing? I imagine it can be manually engaged, just not sure how.

Thanks!

 

[JDToumanian]

TM 9-2320-279-20-1 has troubleshooting for the fan clutch and fan clutch valve...

"Engine temperature must be approximately 195 degrees F and air pressure between 100 and 120 psi before fan control valve can be checked. Remove hose from fan clutch to fan control valve. If air comes out of fan control valve fitting, replace fan control valve. If air does not come out of fan control valve fitting, replace fan clutch."

Basically, the fan clutch is released by air pressure. With the air tanks empty, the clutch should be locked. If the engine is cold and you start it, when the air system pressure builds, the clutch should release and the fan should freewheel because the control valve allows air to the clutch which releases it. When the engine gets hot, the valve shuts off the clutch's air supply which engages it.

My truck seems to run fairly hot too, by the gauge at least, so I need to do a little troubleshooting of my own. It doesn't help the situation that 3/4" of the pointer travel on the temperature gauge covers 130-180 degrees, but 180-240 degrees, arguably more important, gets only the last 1/4" of travel at the far right of the gauge. Because of this non-linearity, it's hard to tell exactly what the actual temperature is. The thermostat is a 180, and the fan control valve is fully closed (fan on) at 202 degrees and fully open (fan off) at 189 degrees. That's per the NSN data for the thermostat and fan control valve. My engine certainly doesn't feel hot, but I want to get an infrared thermometer, or use a lab thermometer to make sure.

Regards,
Jon

 

[dk8019]

Thanks Jon, I read through that section yesterday as well, I cracked the line leaving the fan control valve, and there was pressure on the line when the engine was hot. I think I'll drain the air tanks this morning, as well disconnecting that line and verify the fan clutch locks up. Should know more today!

 

[dk8019]

Jon, sure enough, it locks up with no air. I'll see if I can't locate a new control valve, but I may simply bypass it for the time being.