Does this kind of behavior present itself in the 603 when the headgasket has gone south?

Yup.

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

The behavior observed by the OP is somewhat typical of the 603 under load, however, the climb past 105C. is definitely extreme.

As mentioned, the thermostatic fan clutch in front of the radiator is a key component in keeping this engine below the red zone. Once the engine hits 100C., the fan should be fully engaged and making quite a bit of racket in moving a significant amount of air.

If the fan clutch checks out, the real question is the age and condition of the radiator. If the radiator is original, it most certainly is a contributor to this behavior.

The suggestion that the head gasket is compromised without any supporting evidence other than higher than desired temperatures under load is simply a WAG that is worth nothing.

He lists the radiator as having been replaced; although he doesn't say how long ago. So unless the condenser is completely plugged with 25 years of crud the mystery deepens.

Is the radiator hose still filled with pressure after sitting overnight?

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The radiator is a factory replacement by behr and it is less than 6 months old. The hoses are not still pressurized after sitting overnight.

I'm hoping not. I ordered a engine oil analysis so I should know soon enough.