This is fairly common to newer Marklin steamers. It was mentioned in the October digital club newsletter regarding bridge ramp and approach grades. My br 38 included. As it can be impossible to eliminate all spots on the layout where derailing can occur due to length constraints, I have been able to improve it by bending the copper spring on the axle to apply more downward force on the pilot truck.

On other rolling stock from other makers the wheel spacing is often a source of derailment (large wheel spacing and small flanges). But it is probably not possible to adjust wheel spacing in this case...

To add to marklinist5999. Last evening I experienced a small non Marklin steamer without bogies derailing in a curved turnout. It was a in the left turn in a left turning turnout (if that makes sense..). On closer inspection it was clear that the front right wheel hit the edge of the rail, in what I believe is called the heart piece of the turnout, causing the engine to jump up and derail. The problem was solved by modifying the metal slightly (in the turnout) in order to make a smother passage.

In English, for reasons I don't know, this is known as a 'frog'.
Maybe it is because it causes wheels to jump ...

Guys,

Thank you so much.
So the switch is indeed on an incline and I thought maybe theslicht variation lelevation was causing the problem- I put the switch in a different position so that while still on a incline it is flat to the tracks preceeding and following the actual switch- in other words the loco, which as suggested is long and that can cause the fr4ont or rear bogie to derail. Anyway, that didnt work which was really annoying as had to do quite a bit of work re-working that part of the layout.

So I am starting tosuspect that infact it is the frog of the switch.
I will work on that see if it works.

I now obsessing about getting this to work- it is driving me bananas!!!!!

And happy new year!!
And thx again for your thoughts.