> It was fine for a daily drive of 1 mile each way @ 25 mph.
> But on the highway @ 55 the cooling system was just too
> clogged with rust.

That is the opposite of what I'm experiencing, but Loren's suggestion
makes sense that high speed air velocity may be enough to keep cool,
but the radiator lacks capacity during stop-and-go with only the fan
pulling air through the radiator.

Loren mentioned that the radiator may not be able to be flow tested.
So, how does one diagnose a clogged radiator to decide if it is the
problem and should be replaced?

The radiator in my 85 Westy was replaced in 2006, and only the blue
BMW coolant has been used (50-50 with distilled).  What is the average
lifespan before corrosion of the radiator?

Thanks,
Travis