Oil in radiador, engine runs normal
Check your tranny and engine oil. you are not to have them in your rad. Checking the tranny and oil should help tell you which of them is leaking into your rad.
Plus you don't want to continue to drive it until you correct the issue.
I keep forgetting to point out what is second nature to me, I will try to remember to point out the obvious because you are 100% - some (most) don't know enough to stop driving when they get a flat.
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