Go BottomTC35D temp woes
 | Larry in MI.
Join Date: Posts: 1 
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2001-04-04 26331
I made the necessary fix to the TC35D bypass problem. Everything worked fine for about 3 weeks. Yesterday I was tilling the garden and the temp. gauge went from normal to the cold mark suddenly. I decided to give it a rest for the day. Today I noticed the same problem, the engine warms up, the top radiator hose warms up, and the engine temp. gauge never moves from the cold peg. I removed the wire going to the engine block temp gauge and shorted it to ground. The gauge on the dash immediately went to full scale. I suspect the engine temp. gauge went bad. Does anyone else have a better plan for this problem???
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-04-05 26345
I'd measure the sensor resistance with an ohmmeter. There probably are some specs that give cold, and maybe hot, resistances. If specs are not available, I'd guess that the sensor always should show some continuity, and measured resistance should change going from cold to hot coolant. I'd also verify that the sensor is getting voltage when the gauge doesn't seem to be working. If the gauge moves when the sensor wire is grounded, then the gauge probably is OK. Care should be taken when grounding electrical components without load unless called for in a manual test. ....
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 | BillMullens
Join Date: Jun 2000 Posts: 649 Central West Virginia 
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2001-04-05 26349
Could it be the thermostat opening? If this were the case, if you continued working, eventually the thermostat would close and the temperature would return to normal, then if would open again, etc. Also, have you checked your antifreeze level? Trapped air and/or low level will cause temp gauges to do funky things; sometimes a low level will show "cold" on the gauge because the coolant isn't contacting the sensor, when actually the engine is running too hot.
Bill ....
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| Larry in MI.
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2001-04-05 26364
Thanks Tom and Bill. I checked the coolant level and it is fine. When I grounded the temp. gauge wire it was very brief and I knew I was taking a chance. I am very experienced in electronic circuits and should have thought to check the resistance at the temp. sensor. Normally temp. sensors are nothing more than a temperature dependent resistor housed in a thermally conductive protective casing. I checked it tonight and I believe it is within a reasonable range. It reads about 270 ohms cold and warmed up to 254 ohms. This tells me that the sensor is working and within reasonable tolerances. The only other thing that I can think of that would cause this problem is the thermostat sticking in the open position. Judging from the smell of the exhaust the engine is running cold again. What are your thoughts?? ....
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| david swann
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2001-04-05 26367
I think you are right on. Your symptoms match your diagnosis
David ....
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| Michigander
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2001-04-05 26372
When the service tech came to replace my thermostat in a vain attempt to cure my temp problem. He snipped off a little pin on the edge of the thermostat before he put it in. He said that sometimes this will catch on the spring and hold it open. This was obviously not the problem on my TC40D but you may be having that problem now. I have not put the extra valve in yet as the weather is warmer. My dealer called yesterday to let me know that his contact at NH told him a service bulletin would be coming soon and he would be out to correct the drain hose issue ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-04-06 26377
The sticking thermostat idea sounds as good as any other. Similar to Michigander's comment about the snipped off tag, I found the gasket was installed on the wrong side of the thermostat. However, the problem was excessive by-pass, and the engine wouldn't come up to temperature in cool weather. However, you might think through the original problem. Specifically, how fast the temperature gauge goes from warm to cold. A measured decline would be normal, following opening of the thermostat and entry of cold rad coolant into the engine. However, the gauge maybe shouldn’t go back to full cold, even with a sticking thermostat. An engine warming at idle doesn't product a lot of heat. If the thermostat started out closed, it wouldn’t open fully as it came up to temperature. Cold coolant from the rad would keep the thermostat from fully opening. The flow of cold coolant from the rad would be restricted, and maybe insufficient to completely cool the engine coolant. A rapid gauge decline still could be wiring, depending on how the gauge is set up. The gauge on my 1710 reads full hot when the engine switch is off. With the switch on, the gauge goes to cold and rises as the engine warms. Several times the instrumentation has lost power, which produces a hot reading on my 1710. Your tractor may read cold if the gauge loses power. You might want to ensure the sensor line has voltage and the instrument panel lights come on when the problem is present. Also checking to see if the upper rad hose follows the gauge and goes from warm to cold may be a good idea. Anyway, this is more an approach to thinking about the problem than a diagnostic procedure. I think I’d just replace the thermostat if I had any doubt about it. They aren’t very expensive or difficult to replace (except for whoever replaced the one in my 1710).
....
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| BillMullens
Join Date: Jun 2000 Posts: 649 Central West Virginia
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2001-04-06 26381
Larry, did you notice when checking the sensor output if the resistance varied linearly? I'm curious if the gauges/sensors could be the type that some autos use (Ford is notorious for this); there are gauges on the dash, but they really operate like an "idiot light"; if you notice, the temp and pressure always show one spot or another. Not picking on Ford; I installed a mechanical oil pressure gauge in my Shelby Dodge and left the factory gauge in; the factory gauge had no connection with reality. It just moved about at random, but I would have never known this without the mechanical gauge. The idea of checking the top radiator hose temperature and relating it to gauge temperature is a good one!
Bill ....
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| Larry in MI.
Join Date: Posts: 1
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2001-04-08 26478
Michigander was right on the money. The thermostat had this small "flapper" valve in it. The little metal flap thing had moved over and was holding the thermostat open. I simply cut the the little metal flap thing off and reinstalled the thermostat and everything works fine now. I didn't even have to replace the gasket. Now if I can just fix the hydro leak where the loader hooks on I will be good to go! ....
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| gary mason
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2001-04-09 26511
I had my tc35d out this weekend with air temps in the high 80's. The temp gauge came up to the middle of the green area withing a few minutes of driving it down the road at full RPMs. Stayed there consistantly all working time.
Is this just a cold weather problem?
gary ....
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| Larry in MI.
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2001-04-09 26531
Hi Gary. It was in the low 70's here when I made the fix. My dealer was able to look up the thermostat problem on whatever computer tech line they use. At the time I did not have that problem so I fixed the bypass problem. Everything worked fine for a few weeks and then the cold engine syndrome appeared again. The thermostat problem only showed up after 10 hours of use. If you ever looked at one you would understand how it is a random issue. This little metal flapper (for lack of a better word) sits beside the seal that opens and closes in the thermostat. If everything goes exactly wrong the little metal flapper will get stuck between the thermostat seal valve and cause it to stay open from that point forward. Thermostats are designed to open and close depending on the temperature of the coolant in the engine. When the thermostat is constantly held open by this flapper valve the engine never gets a chance to warm up. This was a very long non-answer to your question. The only way to tell if you have a problem is to determine if you have the defective thermostat by visual inspection or by asking your dealer. ....
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