Case 450 3056051

[Case450bTC]

I will measure my dipstick tomorrow for you, was the final problem with yours the valves on the torque converter housing, i have exactly the same problem after exactly the same issue, bogged to the frame.
I have put a second hand tranny in, new charge pump, new filters, oil changed 4 times. Can drive for 1/2 hour until it gets hot then looses drive

 

[Tinkerer]

Welcome to HEF, Case450TC !
Have you checked the oil cooler bypass like Coy has advised ?
Is the oil cooler clean ?
Not just the outside but also the inside of the tubes.
If they are partially plugged for some reason you will have an overheating issue.
Does the radiator fan blow out towards the front, or pull air towards the engine ?

 

[Case450bTC]

I have taken the line off the oil cooler and run engine while it was cold and the oil was going through the cooler no problems, fan blows out. Haven’t checked the flow while it is hot.

 

[Tinkerer]

A fan belt with a hard glaze on it can be hard to detect. The stupid things can slip at high RPM's and not squeal or make any noise.
Partially plugged tubes in that cooler could be another thing to check if you haven't already done it.
I assume you changed both of the filters. Yes?

 

[Coy Lancaster]

Another problem you could have is the torque converter is slipping.