Thanks Richard, thats where I'm headed but then I noticed the test port and had to ask question. I know on a 727 you can install in the rear test port on pass side and it will give hottest temp, but cannot find any fluid flow diagrams to tell me on 400. I know with test ports you have to be careful not to inhibit fluid flow by installing a probe, so thats the info I was looking into. I'll be looking into my fittings box tomorrow, since I seem to have more selection than my local Earls dealer .