This regards my diesel vanagon. It's not running hot, but the radiator
fan has never come on to my knowledge, and the temperature tends to
creep up in the 90+ heat in long lines of traffic. I want to get this
situation fixed before I get behind some miles-long accident jam.

I am looking for instructions to determine if the fan or the sender is
faulty.

I also understand that later-model senders are set at a different
threshold, and that I might benefit by installing a later model sender.

Also, aren't the later-model fans more robust? If I'm going to be
installing AC in the van, should I go ahead and look for a fan upgrade,
if it will fit?

Thanks,

Jim