What would be the symptoms of a single disc thermostat failure in a two disc system? My JD 790 hoe is running on the hot side but cools very quickly upon idling. I have checked coolant level, blew out radiators and checked temps. On immediate check when HOT, it was 210 below the thermos and 190 above. Could I have one of them failing causing low flow? I may go get 2 180's in the morning and see what happens as it was hot when I left this evening.
Is this the thermostat housing that is a bulge in the cast iron neck several inches from the engine, with a rectangular cover? It should take almost a complete blockage to get those kind of temperatures, I'd think one thermostat working would be enough to keep both sides of the thermostat virtually the same temp. The temp drop from top to bottom of the radiator would be high in that case just like if the radiator was plugged on the water side. I'd check the thermostats at least. How long since the coolant has been changed and what drained out with it?
Yes, the housing is remote from the head and rectangular. It's the same engine as in JD 2000 series farm tractors just juiced up (165 hp). Its a new machine to me (last fall acquired) and low hour (3800). Problem I have with checking temps is hydraulic cooler dumps heat into engine radiator so I could be getting overheat from 2 places. Pump was 185 F at high temp check. Seeing the 210 below the thermo's is what got me to thinking one is stuck. Down here with our temps I'm not real fond of a 190 thermo as there isn't much room to play above it. I can't get to the top and bottom tanks to get a temp differential reading but looking at the core under the cap it doesn't look too bad.
Update on overheat problem. I got a new 180 F thermo and pulled coolant manifold off. It is only a single disc system with one of the possible ports solid with a small hole in the center for I would assume a low flow bypass. Today was a little cooler and the machine ran a bit lower accordingly but not much. I now am starting to wonder about something in the hydraulic system instead. I am clearing lite timber with it so not really overloading it unless one doesn't want to come out of the ground. I'll recheck with temp gun next week when our ambient temp is higher.
Are the fan belts good and tight ? Any chance they may be glazed and slipping even though they are tight ?
I think I have finally figured out the cause of the overheat and hopefully the fix. The hydraulic system is going onto high pressure during no load and deadheading. I unplugged all the pump sensors one by one and found that the pump outlet pressure sensor seems to be the culprit after it heats up as unplugging it unloads the system. I have a new one ordered and will see if that fixes it. I will also check the belt but on changing out my harmonic damper ring, it seemed to be holding the fan well.