Thermistor Replacement

[Brimstone10x]

Hey guys , you all will think Im crazy but Ill give my two cents on the 4300 thermister. yes the thermisters go bad however a large part of the problem is that the fuel shut off solenod gets oil in it and that causes the plunger to take longer to pull in and the thermister trips off before the plunger pulls in. So what I have done on a few of these is to replace the thermister with a circut breaker , I think 5 amp useuly does it . and yes extending the wires so you dont have to remove the load center makes it easyer to deal with. some of these tractors are habitchual ofenders, and get worst in the cold due to the oil in the solenod. Many fuel solenods get replaced because of this for no reson . A circut breaker is way cheeper than a solenod. good luck:thumbsup:

 

[JD755]

Hey guys , you all will think Im crazy but Ill give my two cents on the 4300 thermister. yes the thermisters go bad however a large part of the problem is that the fuel shut off solenod gets oil in it and that causes the plunger to take longer to pull in and the thermister trips off before the plunger pulls in. So what I have done on a few of these is to replace the thermister with a circut breaker , I think 5 amp useuly does it . and yes extending the wires so you dont have to remove the load center makes it easyer to deal with. some of these tractors are habitchual ofenders, and get worst in the cold due to the oil in the solenod. Many fuel solenods get replaced because of this for no reson . A circut breaker is way cheeper than a solenod. good luck:thumbsup:

Just trying to understand what you are doing. Are you saying you only have a circuit breaker in series with the pull-in coil of the solenoid? Are you counting on excess current tripping off the circuit breaker about a second after power is applied? Is it a manual reset you need to reset at every start? Is it an auto-reset that will keep reapplying power and tripping back off? Since the solenoid coil is not designed for continuous power, what is the method of removing power to it after start?

 

[Brimstone10x]

Sorry I should have said auto reset type. yes the breaker trips and power is cut to the pull in coil. I dont have the theroy of operation for that circut in front of me but it works . As I said some will think its crazy but I think the thermister set up is a little crazy as well . Im sure deere would NOT approve of this. or an electrical engineer.:thumbsup:

 

[tglass]

Question? what exactly is a Thermistor? never understood this. more or less a solid state relay or what?

 

[kennyd]

Question? what exactly is a Thermistor? never understood this. more or less a solid state relay or what?

This is easier than typing, sorry: Thermistor - Wikipedia, the free encyclopedia

and http://encyclopedia2.thefreedictionary.com/Thermister

 

[tglass]

Very good explanation. Thanks.

 

[JD755]

Sorry I should have said auto reset type. yes the breaker trips and power is cut to the pull in coil. I dont have the theroy of operation for that circut in front of me but it works . As I said some will think its crazy but I think the thermister set up is a little crazy as well . Im sure deere would NOT approve of this. or an electrical engineer.:thumbsup:

I'll just have to say that is not a good thing to do to a solenoid. Continually sending never ending (during tractor operation) on-off power to it will really shorten its life. Overheating and burning out is a real possibility, along with simply wearing out the mechanism. Yes, I am a retired aerospace EE.

If you really want to eliminate the thermistor, my suggestion would be to change to what Deere used on the x55 tractors like my 755. The pull-in coil is simply connected to the starter. Solenoid has power as long as you crank the engine, and goes away when it starts and you turn the key back from Start position.

 

[JD755]

I'll just have to say that is not a good thing to do to a solenoid. Continually sending never ending (during tractor operation) on-off power to it will really shorten its life. Overheating and burning out is a real possibility, along with simply wearing out the mechanism. Yes, I am a retired aerospace EE.

If you really want to eliminate the thermistor, my suggestion would be to change to what Deere used on the x55 tractors like my 755. The pull-in coil is simply connected to the starter. Solenoid has power as long as you crank the engine, and goes away when it starts and you turn the key back from Start position.

Analyzing the 4300 schematic I find there is an additional relay coil in parallel with the thermistor, and in series with the solenoid coil. When the thermistor heats up and increases resistance, that increases the voltage across the relay coil and allows it to engage. The relay contacts then open the connection to the thermistor. This leaves just the relay coil in series with the solenoid coil. Since the relay coil is a much higher resistance than the solenoid coil it will have most of the voltage across it and leave very little across the solenoid coil. This relay would prevent the power ratcheting action I was concerned about if using an auto-reset circuit breaker in place of the thermistor.

 

[HorseCrazy]

I just registered for the sole purpose of saying THANK YOU!

After months of intermittent starting on my Deere 4300, heartbreak in a blizzard when I need to snowblow our long driveway, etc., banging my head against the wall trying to figure out why my tractor wouldn't start . . . and then sometimes it would . . . well, I finally Googled enough to stumble across mention of that evil little thermistor -- on this site and several others on the web.

Ordered one a week ago. Got by using the "short out the white solenoid wire briefly" trick while I waited for the part to arrive -- which worked every time. Soldered the new thermistor in today. Problem seems to be solved.

I really appreciate all the collective knowledge here. You guys are incredible.

 

[JD755]

Welcome! to TBN HorseCrazy.

Really glad the information was useful to you. Spend some time using the Search feature and you may find lots of other useful information here.