Exhaust temperature specs/operating range

[muhoo]

My 1998 E350 seems to be getting hotter and hotter all the time. I can feel the heat through the doghouse, and didn't used to be able to. Coolant temperature is normal.

The turbo and EBPV is covered in bright red rust (I cleaned it off, but I have to wonder why that happened), which has never been a problem before.

I checked that the EBPV is fully open, which it is, and it doesn't seem stuck. I may have an exhaust obstruction or plugged muffler, I dunno.

What is the normal exhaust and/or oil temperature at WOT? I don't have an EGT but I buddy has a laser touchless thermometer I could borrow. What would be normal readings, and what would be out of spec?

Thanks.