Fan clutch?

[jeepit]

Noticed my coolant temp guage fluctuating yesterday while towing. From just above 190 then down to 180. The weather temps were between 30-40 degrees. This morning when I started the truck I noticed the roar of the fan with the fan clutch engaged. Isn't it only suppose to engage when the air temp is hot? Could this be why the guage was fluctuating?

 

[SRadke]

They commonly engage at cold startup for a short time. Your temp fluctuation was likely caused by the thermostat.

-Scott

 

[PBJ2500CTD]

This is normal. The clutch will be engaged during the first few minutes of operation when cold. The fluctuation seems to be a "feature" with the gen 2 trucks. My 98. 5 and 02 have both fluctuated. The 98. 5 was load related while the 02 just happens when it wants to. I have changed a number of thermostats with no real change in temp fluctuaions. Another possibility could be a radiator cap issue and/or air in the system.

From the FSM:

It is normal for fan noise to be louder (roaring) when:
...
Cool silicon fluid within the fan drive unit is being redistributed back to its normal disengaged (warm) posiion. This can occur during the first 15 seconds to one minute after engine start-up on a cold engine.

 

[1995Dodge...]

Food 4 thought on eng temp's & thermostats.

DIESELSITE 203* Thermostat... .

WHY IS 203* BETTER THAN 195*?

Diesels run most efficiently at approximately 200o or above. A factory equipped 192o/195o thermostat will maintain an operating temperature at approximately 165o-170o. The Powerstroke has such an efficient cooling system, that this low flow when the thermostat is slightly open is normally enough to keep the engine cool. The downfall to this is that the engine -- when our trucks are not under load --never begins to reach its optimal operating temperature. Our 203o thermostat maintains a minimum operating temperature of 190o. This brings the operating temps up from as low as 170o to as high as 203o depending on the operating conditions of the truck. This is closer to the operating temperature range that is preferable in our trucks for optimal efficiency.



When our trucks are under load and are producing higher combustion temperatures the 203o will allow the engine to run even closer to its optimal operating temperature. If the truck is under load and reaches the 203o setting, the thermostat is then fully open. This means you are at the maximum coolant temperature that the truck will reach. Your maximum temperatures are only a few degrees higher than in stock configuration, but these are degrees that you want for better performance. The best benefits come when the same truck is under a light load and would have a hard time reaching this optimal temperature. As stated above, you will never reach this optimum temperature with the stock 195o thermostat. The end result of installing the 203o thermostat should be slightly better fuel economy, less smoke, and maybe a few extra "ponies" to go along with it.

 

[DonTX]

My "fluctuation" got worse and worse. Finally when starting for the day, it would go very high, then very cold. Turned out the thermostat was "sticky", took a lot to break it open, then it got doused doused with cold coolant. A new thermostat settled it down to normal.

 

[EricBu12]

My new 09 has a very stable temp. I tow a 15K trailer and no matter what, climbing hills, pushing wind, or running easy. . it never gets one needle width above 200deg. . . dont go below it either.