Arthur- the 4-prong MB sensor I'm using decreases resistance as the temperature increases (approx. 970-ohms @ 44C and 186-ohms @ 100C;
sensor range: 870-ohms;
The Derale's radiator probe also decreases resistance as the temperature increase (apprx. 5.5Kohms @ 44C and 2.24Kohms @ 100C;
sensor range: 3.26-ohms
Derale preferred trigger point: 3.3kohms @ 93.3C
BTW- what 4-prong MB sensor are you using?