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Southern Illinois | Having hydraulic heating problems on a Magnum 250 CVT. Planted lots of beans this spring and one day of double crop. The next day it ran 20 min and the hydraulic oil alarm came on. Had a spare tractor so didn't mess with it.
New filters this spring, cooler is clean. Drove it about 5 miles today and the oil got to 180. Temp gun said nothing on the tractor was that hot. Trans and hyd filters were 120 and I could put my hand on them. Transmission and rear end were 110. I changed the temp sensor and changed the one for the transmission by mistake. I wasn't aware they show the trans and hyd temp separately, maybe that's a CVT thing. Just sitting at half throttle the hyd temp went from 160-190 in 15 min. No hyd load, no driving. I verified the cooler temps again. 100 in 75 out. Air temp 77.
I found the hyd temp sensor in the big tube that comes off the bottom right side and goes up to the charge pump. I plugged in the temp sensor I changed earlier and it read air temp as it should have. Then hyd temp was reading 190 but the location around the sensor was not hot to touch.
My only other thought is to go through the hyd cooler bypass. The older magnums I had done them on had a mechanical valve. These show an electric bypass valve in the parts book (searched with the serial number so I was sure I got the right one). Looks like they just have a spool and a solenoid and a few orings on them. How hard of a job are they and where are they on the machine.
I am open to any other suggestions to what I might be missing. Once I found out they show trans and hyd temp, the transmission temp was not climbing. Is the next thing to do is change the hyd temp sensor, it is easy enough to get to but I will make a small mess, but that's okay. I just feel like since it worked one day and we were rained out a few days then it didn't work points to electrical and hopefully a cheap sensor. Thanks everyone
Edited by ag4life 7/31/2025 19:52
 (Screenshot 2025-07-31 195436 (full).jpg)
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 Screenshot 2025-07-31 195436 (full).jpg (26KB - 7 downloads)
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Magnum 250 CVT hydraulic cooler bypass
