120hp Johnson Outboard??

[THEFERMANATOR]

If you have the white housings, DITCH THEM IMMEDIATELY! OMC issued a bulletin years back about overheating caused by the white housings. The white t-stat housings have a guide on the end of them to help center them in the seat, but all it did was cause overheating as the rubber got older in the seat and wouldn't let them move out when the valve would drop pressure. The black housings are the only housings you are supposed to use now. Inside they both use the same vernotherms, and open and close at the same temp. Clean out the valve that SKOOLS posted, and make sure the linklage is hooked up working to it. Next get a set of the black t-stats and diaphrams and your problems will most likely be over. Also the stats should open up at 160, so it sounds like the springs inside your stats are work hardened from the years anyways. Also pay attention to how the valve comes apart as the valve can be installed 180 degrees out and it won't function properly that way.