is there a special test to check how oil pressure is in a van?

Answer 1

yes, its called an oil pressure test ;)

remove the oil pressure idiot light switch from the engine and put in either an eletric sender for an electric gauge, ot a small pressure line for a manual gauge.

rule of thumb is 10 psi at idle and 10 psi over that per 1000 rpm

Answer 2

Yes. You remove the oil sending unit and install a master or mechanical gage and check the oil pressure that way. To get an accurate check on the oil pressure let the engine warm up completely.