The title kind of says it all. I have an 2008 f350 diesel and I was driving down the road while it was -12 degrees Fahrenheit and all of a sudden the fan ramped up all the way. Then the engine temp gauge slowly crept up. I had to drive going 50MPH or above to keep enough cold air going through the radiators fast enough to keep the gauge from red lining. Any ideas what could be the problem? Coolant level is normal, no pending or stored codes, and the coolant temp was hovering around 170 degrees. The millage is 156,000 adn the truck is in good shape other then this.

 

170degrees is not near hot enough for a PSD. You should be running close to 190 degrees, although that is probably not going to happen at -12. I see 182 to 185 when it is that cold here in MN. with the factory thermostat. Normally I run a Mishimoto 200 degree stat in the winter, but didn't get it installed this year. I would make sure that the temp reported before start up in the morning shown by a scangage or other monitor is close to the outside ambient temp to make sure the sensor is correct. Assuming the sensor is accurate I think you either have a bad stat or possibly a bad fan clutch, it should not be running 100% at 170 degrees. Are you getting any heat from the heater and are your radiator hose just warm or hot? With the fan on at 100% and the temp gauge red lining you may also have too weak an antifreeze mix, causing it to freeze up, not likely but possible, or your water pump impeller could be loose on the shaft and not moving coolant as it should. I guess I don't quite under stand a coolant temp showing 170 and also redlining the gauge all at the same time.

 

I had a Toyota once that every winter I had to remove the t-stat.
for some reason they would stick. And not open during the winter. “ go figure”
but like jetjockey99 I bet the issue is the t-stat.

best of luck

 

There are more variables feeding the cooling fan operation than just engine temp -- using just engine temp is NOT how the system operates -- the PCM is using many others to drive it (e.g trans temp, outside air temp) -- really need a scan tool / instrument that can monitor and change the variables to diagnose the underlying problem.

 

Ya I have a monitoring tool. But I think I've narrowed it down to a bad anti freeze mixture or a bad pressure valve to the radiators. It can't be a bad fan clutch because the fan only comes on when the trucks begins to overheat. this problem has only come up once before and it was also below -10 degrees. So I think its just that the anti freeze is sloshing up because it's so cold, I'm going to get it tested tomorrow.

 

North Indiana been in the single digits. My truck isn’t completely warmed up until 195ish.

 

The fan comes on as commanded by the ECU, it is part of the sequence as the motor warms up - no concern unless it stays on for extended periods of time.