I think I've solved the problem, and I feel pretty stupid about what I found.
More and more, the symptoms kept pointing to an overheated transmission. But why would the transmission overheat when the engine wasn't? It's probably due for an oil change, but certainly not critically overdue. So I had resigned myself to having the tractor hauled to the dealer, 100 miles one-way. I don't like asking mechanics to work on dirty equipment, so I decided to clean it up yesterday and get it ready for the pros.
While washing the dust off engine, I noticed something that I'd never noticed before. In front of the engine radiator, behind the transmission oil cooler, there is a screen. The screen fits tight against the front of the engine radiator and is painted black just like that radiator. The transmission oil cooler is a natural aluminum color and there is a small air gap between the two. The oil radiator was clean, save for a tiny amount of dust.
But that screen was clogged. It looked like a clothes drier lint filter after the first drying of new towels. The screen lifts out easily. I cleaned it off and replaced it. I finished giving the tractor a bath and let it drip dry for a couple hours.
Then I went out and started it up, and started working it. I ran it for over an hour grooming erosion out of my driveway and I had no problem. Recent attempts to work the tractor have only lasted about 15 minutes or so - just long enough for the transmission to get up to working temperature (or so I theorized - I've never seen any idiot lights warning of high trans oil temp.) I haven't been able to get more than 15-20 minutes work out of it for last several times that I've attempted, so working without shutting down for over an hour leads me to think the problem is solved.
I don't know why the engine wasn't running hot. According to the engine temp gauge, it was normal. Even though the oil cooler was unobstructed, there would have been little airflow through it because the fan wasn't able to draw air through the engine radiator.
If this was the problem, I'm very disappointed that there was no transmission overheat idiot light indication. A hint like that would have been very valuable. Now I want a temp gauge for the transmission.
More and more, the symptoms kept pointing to an overheated transmission. But why would the transmission overheat when the engine wasn't? It's probably due for an oil change, but certainly not critically overdue. So I had resigned myself to having the tractor hauled to the dealer, 100 miles one-way. I don't like asking mechanics to work on dirty equipment, so I decided to clean it up yesterday and get it ready for the pros.
While washing the dust off engine, I noticed something that I'd never noticed before. In front of the engine radiator, behind the transmission oil cooler, there is a screen. The screen fits tight against the front of the engine radiator and is painted black just like that radiator. The transmission oil cooler is a natural aluminum color and there is a small air gap between the two. The oil radiator was clean, save for a tiny amount of dust.
But that screen was clogged. It looked like a clothes drier lint filter after the first drying of new towels. The screen lifts out easily. I cleaned it off and replaced it. I finished giving the tractor a bath and let it drip dry for a couple hours.
Then I went out and started it up, and started working it. I ran it for over an hour grooming erosion out of my driveway and I had no problem. Recent attempts to work the tractor have only lasted about 15 minutes or so - just long enough for the transmission to get up to working temperature (or so I theorized - I've never seen any idiot lights warning of high trans oil temp.) I haven't been able to get more than 15-20 minutes work out of it for last several times that I've attempted, so working without shutting down for over an hour leads me to think the problem is solved.
I don't know why the engine wasn't running hot. According to the engine temp gauge, it was normal. Even though the oil cooler was unobstructed, there would have been little airflow through it because the fan wasn't able to draw air through the engine radiator.
If this was the problem, I'm very disappointed that there was no transmission overheat idiot light indication. A hint like that would have been very valuable. Now I want a temp gauge for the transmission.