John Deere 6620 water pump question

Moline_guy · Sep 23, 2016

I bought a 6620 from not too far away, on the way home it was running warm, not into red but close. Engine and top radiator hot, but lower radiator cold. I put in two new thermostats from Deere and same program. With both thermostats in it circulates hot water up to cab heater, but does not seem to move any water through the radiator. Radiator looks clean and had been replaced at some point. When draining and pouring water into and out of radiator it seems to move through the radiator as fast as you can pour. I removed one thermostat and ran it a bit this way and the radiator stays warm top to bottom and there is a lot of movement looking through the open radiator cap. Can i run with one thermostat out? Does a water pump "wear out" that I need to replace the water pump to push the water through the thermostats? Any ideas or suggestions as to what is going on here? Thanks for any help.

casecollectorsc · Sep 23, 2016

Not being smart but wouldn't a radiator be warm on top from hot engine coolant and cool on the bottom from the water cooling going thru the radiator? If you have good movement one would assume the pump is good. Leaving a thermostat out lets coolant move too fast to cool going thru the radiator. Are the fan belts new and not bottoming in the pulleys. Should be able to pull on the fan and turn engine if all is good.

Janicholson · Sep 23, 2016

Not a flame: As the speed of water going through the radiator increases, (and assuming fan operation, and no dirt plugged fins) the greater the heat removed. Delta T is change in temperature. The hotter the entire radiator is, the greater the heat removed from it by the air flow, at a given air temp. Thus removing the thermostat lowers the engine temperature more than having a thermostat in the system. It may not seem correct, but it is truth. The purpose of the thermostat is not to control the speed of water, it is to maintain running temperature of the engine. When approaching any temperature above where the gauge is normally pointing, opens the thermostat more until the point at which it is fully open and flow is not restricted, cooling to the max. A bad thermostat can restrict flow and thus promote overheating. Jim

Steve@Advance · Sep 23, 2016

Circulation through the heater says the pump is working. It is very rare for a pump to not move coolant. It is possible for the impeller to rust away, but takes years of system neglect for that to happen. I've only seen one impeller fail, a plastic one that split and fell off, of course there was no movement at all.

Are you sure it really is overheating? Can you verify the temp gauge is accurate? Did it still show high temp with the one thermostat out?

If it ran cool with one thermostat out, I would replace both thermostats. That would be the easiest and least costly first approach. Then see what happens.

If it still overheats (and you know the gauge is good), look for symptoms of a head/head gasket problem, such as mysterious loss of coolant with no external leak, over pressurizing and blowing coolant out the cap, water condensation under the oil cap, valve cover, dip stick tube.

bigbob1939 · Sep 23, 2016

It is very possible that the impeller on the fan shaft may be loose and not turning as fast as it should or the fins on impeller are deteriorated to where they dont move enough water. I had a water pump do this in a sbc. Bob

jared in wi · Sep 23, 2016

I would check the air flow through the radiator first before diving too far in to the cooling system. There are some additional coolers in front of the radiator. There could be some dirt or debris between the coolers. Also, blow out each of the coolers individually to see if any debris comes out. Make sure that you don't bend over any of the fins.

Jared

MN Scott · Sep 24, 2016

Have to disagree with you. If you remove the thermostats the engine will run hot or overheat as the coolant will run thru the radiator to fast for the heat to be removed. I've seen this several times over the years. Friend of mine decided he was going to race stock cars several years ago. He bought one and asked me to be on pit crew. He had done some work on it himself and the first night out it overheated on hotlaps. He couldn't understand why as he had removed the thermostat so the coolant should be flowing well thru the radiator. I found a washer with a 5/8 hole in my truck and put it in place of a thermostat and problem solved, it ran cool. I have also seen it on trucks mainly were they were starting to run hot because of a bad thermostat or plugging radiator. Guys would pull the thermostat thinking the increased flow would aid in cooling but all it did was change a running hot condition to a boil over condition. The thermostats serve two purposes, allow the engine to warm up to a operating temp and also to slow the flow of coolant to allow time for the heat to transfer to the airflow thru the radiator.

John Deere 6620 water pump question

Moline_guy

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casecollectorsc

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Janicholson

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Steve@Advance

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bigbob1939

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jared in wi

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MN Scott

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