The following have been replaced: thermostat, clutch fan, radiator cap, water pump (wasn't running hot until clutch fan was replaced and radiator flush was done) We were told the clutch fan was out but had never run hot until after replacement. Van has newly rebuilt transmission and we believe we have the air pockets out. We have reason to believe it is not the head gasket. Please help with other ideas.
overheating on 1996 Dodge Ram Wagon 3500
by gottoknow in Augusta, GA on March 15, 2011
ANSWER by raiderron on March 15, 2011
Sounds like you may have put the fan back on the clutch wrong, you may have accidently flipped it over and is now not sucking air across the radiator. You can run engine and hold a towel in front of the radiator or a/c condensor and see if it sucks the towel to it. Be aware that when flushing a rad it is not a repair, it is a maintenance procedure, there may be hot spots and cold spots on the core surface that is indicative of coolant not moving freely inside the rad core. Can measure with infrared temp gun to verify.
ANSWER by Johnny Mopar on March 17, 2011
The thermal viscous fan drive is a silicone fluid filled coupling used to connect the fan blades to the water pump shaft The coupling allows the fan to be driven in a normal manner. This is done at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher engine speeds. A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit. This spring coil reacts to the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air temperature from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will remain at a reduced rpm regardless of engine speed. Only when sufficient heat is present, will the viscous fan drive engage. This is when the air flowing through the radiator core causes a reaction to the bimetallic coil. It then increases fan speed to provide the necessary additional engine cooling. Once the engine has cooled, the radiator discharge temperature will drop. The bimetallic coil again reacts and the fan speed is reduced to the previous disengaged speed. If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns when spun by hand), replace the fan drive. This spin test must be performed when the engine is cool and engine off. Engines equipped with serpentine drive belts have reverse rotating fans and viscous fan drives. They are marked with the word REVERSE to designate their usage. Installation of the wrong fan or viscous fan drive can result in engine overheating. Double check belt routing as you may have the fan turning in the opposite direction it was intended to. For the following test, the cooling system must be in good condition. It also will ensure against excessively high coolant temperature. WARNING: BE SURE THAT THERE IS ADEQUATE FAN BLADE CLEARANCE BEFORE DRILLING. Drill a 3.18-mm (1/8-in) diameter hole in the top center of the fan shroud. .Obtain a dial thermometer with an 8 inch stem. It should have a range of -18°-to-105°C (0°-to-220° F) Insert thermometer through the hole in the shroud. Be sure that there is adequate clearance from the fan blades. Connect a tachometer and an engine ignition timing light (timing light is to be used as a strobe light). .Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser) Use tape at the top to secure the plastic and be sure that the air flow is blocked. .Be sure that the air conditioner (if equipped) is turned off WARNING: USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN A DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE CLOTHING. Start the engine and operate at 2400 rpm. Within ten minutes the air temperature (indicated on the dial thermometer) should be up to 88° C (190° F) Fan drive engagement should have started to occur at between 74° to 82° C (165° to 180° F) Engagement is distinguishable by a definite increase in fan flow noise (roaring) The timing light also will indicate an increase in the speed of the fan. When the air temperature reaches 88° C (190° F), remove the plastic sheet. Fan drive disengagement should have started to occur at between 57° to 79° C (135° to 175° F) A definite decrease of fan flow noise (roaring) should be noticed. If not, replace the defective viscous fan drive unit. Start the engine and operate at 2400 rpm. Within ten minutes the air temperature (indicated on the dial thermometer) should be up to 88° C (190° F). Fan drive engagement should start to occur at/between:
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