I been working on a 92 4X4 S-10 with a 4.3L engine and 5 speed manual transmission. I have encountered something I never have before. The engine will not heat up to operating temperature. I have put about 4 thermostats in it all with the same results. I am putting 195 thermostats in it and have gotten them from GM, Autozone, Napa, and Advance.The engine will reach about 160 and that is it. I have checked the coolant with an external gauge and the gauge in the truck is real close. It will however warm up on hard pulls and in the summer when the weather is warmer.It still has the stock radiator and fan. My brother bought it new and I dont remember it running that cold. All the other S-10's I have worked on ran about 190-200. I have an 89 S-10 and have always done the work myself. I dont pretend to know it all but if I can be of any help to anyone I would be glad to. Thanks for you time and any advice you might have.