Cujo8 - This is from an article in the tech tips section of inliners international. "In pure big truck form the 261 has a larger thermostat housing holding a double acting thermostat. This is designed to circulate water through the block and head before the thermostat opens to allow hot water into the radiator. Thus, no internal steam hot spots during warm ups, especially in winter. This is particularly important with very cold coolant. Vital engine spots can become very hot before the total coolant becomes hot enough to open a normal thermostat on the front of the block." You can tell it's a thermo housing from a 261 if it has 2 holes drilled for the smaller hose fittings in addition to the large one that feeds from the radiator. It is slightly larger than the 235 housing and it contains a hard to find by-pass thermostat. 4onthefloor turned me on to this for waterheating my intake and I couldn't be more pleased with the results. Thanks again!
