Depending on your location in NM, a straight grade may or may not be a good choice.
You can buy a bottle, send it off for VOA info, and then decide if it's a good choice or not, but personally I'd stay clear and just use a decent inexpensive 15w-40 or 10w-30.
The old 6.9IDI was spec'd for 10w-30 or straight 30, but that does not apply to the PSD.