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John Deere 6620 temp gauge says hot. Engine runs fine.

A

andy r

Member
I noticed the temperature gauge on my John Deere 6620 sidehill was running hot. I question whether it is right and if the gauge has went bad? I know what a hot engine does - once the automatic tightener broke which I believe was on the fan. The engine heated right up and made the radiator cap release. The gauge is in the top category but the radiator is not boiling over. I had just washed the fins on the radiator to remove bean dust. Also, the coolant had been topped off. All of the belts are on and tight enough (fan, water pump, and rotary screen). When running I can see coolant rushing across the top of the radiator when the radiator cap is off. Coolant is 50/50 mix. Certainly I do not want to harm the engine, but I can't see anything wrong. I want to finish my last 40 acres of soybeans. Just remembered that I did change the alternator at the beginning of harvest so maybe I need to recheck that belt as I believe it runs the water pump as well. Could I have a stuck thermostat? Should I take the thermostat out? Thanks for your ideas.
 
Believe it or not thermostats aid in proper water flow besides regulating the temp.....leave it in....if it's working correctly. You can test it on your kitchen stove with a pot of water, a candy thermometer for the proper heat range and a string....just hang it by the string embedded in the butterfly to housing interface, submerge in the water, when it falls off check the candy thermometer. Look at the stamping on the pellet and you have your answer. Harbor Freight has non-contact Infrared Thermometers for about 25 bucks...one of the better tools in your tool box.

On checking the fan belt, and you did say you changed the alternator which means you did diddle with the fan belt tension, check for proper tensioning like Den suggested. My test is to see if I can turn the fan without turning the engine over. If I can, the belt is too loose. Proper tension does matter, especially on high volume air movers like tractor engines.
 
The idler pulley arms for the belt tensions get dirt and/or corrosion in them. Make sure that they move freely and apply penetrating oil to the arm shaft. Springs can get weak or break as well. If you have a thermal gun it never hurts to double check temps such as the thermostats.
 
Do not remove the thermostat, just as Texasmark said. I would replace the sensor for the gauge - but if you're in a hurry- I would check the engine temperature with an infrared thermometer. Or drop a thermometer probe down into the top of the radiator when you see the coolant circulating. You are right: if its not boiling over, its probably not overheating. Mark.
 
The fan drive is separate from the water pump - alternator drive. OP should check belts for wear for all. They can wear to the
point of allowing things to slip.
 
On my 6620 the gauge has to be a little above the line for operating/ hot for boil off. Could be anything but belts, tensioners for the fan could be an issue. Or the belt for the pump. One time a mouse had chewed one of the wires for the sender and that gave a false reading.
 
4455 temp gauge would show it was running hot just doing some light disking and unloading corn from the cart into a semi. Did everything, had the radiator cooked, new thermostats, coolant,belts. It was the micro processor in the gauge cluster. $1500 for the gauge cluster and it barely gets to the middle of the temp gauge.
 
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