Coolant temperature

Hello, specialists.

When I bought my V8, it didn't come to temperature at all. So I was the first to change the cooling water thermostat. Then it came to temperature, but in my opinion simply too high. (Temp.-display between 1 and the first zero of 100 degrees). Especially in the summer I had to always manually the 3. The fan level was switched on and thought that this would be u. U. at the viscofan.
But now that it is rather cold, the cooling water temperature remains so high.
To be sure, I measured the resistance of the donor and that was almost 100 degrees at 135 ohms. This value is lt. Rep. book within the framework.
What I'm terribly surprised is the fact that the top cooling water hose from the yl. head is really hot, but the return (below the cooler) becomes max hand warm.
The question is, isn't the new thermostat defective?
Who has documents about the cooling water circuit or. Can I get any help here?
I'm grateful for all the tips.
Best regards from peter