I can't speak to the Mastiff but i have a K-9 that i bought the Ridgeback oil temp guage for 9.99 off e-bay. The problem with the Ridgeback gauge is it is to long (about 3/8) it will screw into the oil tank but bottom out, not tighten. SO. I went to the local hardware store and bought a rubber grommet much like the o-ring that the gauge comes with only thicker about 3/8 thicker now it will snug down:2thumbs:
just sayin'