I use Bars leak in all my tractors, and also ones with thermosyphon (no water pump). However, Gene is correct that you can muck up a radiator if you don't use the Bars leak correctly.
Here is the right way.
Get the tractor up to running temp where she is cycling the coolant. Pour in the Bars leak. Put the cap on and run her for at least 30-40 mins, work her if you can. Take a ride, but keep her running and up to temp.
That will thoroughly mix the bars leak and more than likely fix your problem. However, if you don't get her up to temp and don't run it for at least 30-40 mins at operating temperature, you will have issues.
Sometimes I hesitate to suggest Bars leak on the thermosyphon, because people tend to be lazy. If you do it right, it is fine. If you cut corners, Gene is spot on the money.
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