JD 3720 Cold Start Issues

jloven · Jan 9, 2015

All of the sudden I can't seem to get our 3720 to crank. We have plugged the block heater in for several hours (overnight) and temps are in the low 20's now but when I turn the switch, nothing happens. The glow plug indicator comes on and stays on along with the warning light (! light). You can hear the click-click-click but the glow light never goes out (over an hour of waiting presently). Have the battery jumped and getting 14.8 volts at the terminals. Would it be that the glow plugs are not heating or a sensor somewhere is not closing in the starting circuit or something else?

beenthere · Jan 9, 2015

"Will not crank".. To me that means the starter doesn't turn the engine over i.e. crank.

To some, it might mean the starter turns the engine over, and over, but the engine will not fire and start.

Sounds like you may have a bad battery issue, or poor terminal connections that a cleaning might fix.

jloven · Jan 9, 2015

Will not crank in this case means there is no closure of the starter solenoid, nothing happens when the switch is turned fully clockwise. What is preventing the switch to engage the starter solenoid is the question. Not sure what sensor(s) are involved or if it could be the glow plugs are not heating the cylinder to a temperature adequate to allow the starter to engage??? We have the battery jumped and have 14.8 volts on the fuse buss, eliminating the battery and terminal problem. Called the closest dealer, and all he could suggest is to roll it out in the sun....I think its something electronically is not allowing the starter to be engaged. Also, the dash lights are not coming on and off like they typically do.

kennyd · Jan 9, 2015

If this is the original JD "Strongbox" battery than I'd bet that's your problem. There are tons of threads in this forum about them...yes I know you jumped it and have the correct voltage but maybe it goes shorted internally when trying to deliver the proper current.

Spindifferent · Jan 9, 2015

I would try a known-good battery before anything else.

Beltzington · Jan 9, 2015

jloven said:
All of the sudden I can't seem to get our 3720 to crank. We have plugged the block heater in for several hours (overnight) and temps are in the low 20's now but when I turn the switch, nothing happens. The glow plug indicator comes on and stays on along with the warning light (! light). You can hear the click-click-click but the glow light never goes out (over an hour of waiting presently). Have the battery jumped and getting 14.8 volts at the terminals. Would it be that the glow plugs are not heating or a sensor somewhere is not closing in the starting circuit or something else?

It may not be the cold. There is a starter relay (not sure if that is the official name) that will sometimes cause similar indications. Sitting in the seat directly between your knees on the console is an access door that is clipped closed. Open it and you will see three small square black relay modules, blow all the dirt from around the relays, if you haven't done this recently it is most likely full of dust. Then, I believe it is the far right relay, but it may be the center, pull the relay and clean the contacts and reinsert. See if it starts. I had do this allot until I cleaned the contacts with a fluid.
Good Luck

LoudonNH · Jan 9, 2015

20 degrees is not cold enough to keep your tractor from starting. If it were cold enough to give you trouble, the motor would still turn over but might not fire off as soon as you expected. I agree with the others; you probably (hopefully only) have a battery issue.

Also, I'm not sure how your pre-heater functions; the one that operates with the ignition key. We have three Deere's that all function differently; one works when the key is set to on and shuts off on its own after a few seconds. Sometimes we have to cycle it several times before the motor will fire off in the cold weather. Another functions when you push the key in and has an indicator light that glows while it's on and the third works that way but without an indicator light. Each tractor seems to behave differently in the extreme cold.

All this offered for whatever it's worth...

Cocre · Jan 9, 2015

The only way to eliminate the battery is to remove it and place it 50 feet away so that you will not be tempted to jump start the tractor. Try a known good battery, it will most likely crank. I know my 3320 did when I had some very odd issues trying to start the machine years back.

jloven · Jan 10, 2015

I checked the starter relay this afternoon by swapping with the other two identical relays but did not seem to make any difference. Also checked the 30 amp fuse and it was good. Battery is less than 1 year old and we jumped it straight to the starter and it turned it over just fine, just wouldn't start probably due to the fuel relay not opening. In any event I guess I will load it up tomorrow and take it in for repair. Without the schematic it's impossible to know what is in series with the starting circuit. I am still betting it's some sensor or switch that is not working properly.

beenthere · Jan 10, 2015

Hope they find the problem easily.
For future problems, might be worth the $$ to get a copy of the tech service manual as it will be a good source for trouble shooting. Less than an hours time at the dealer shop.
Thanks for the update on the battery being a year old.