How do you replace a thermostat on a 1977 442 Oldsmobile?

Answer 1

It's at the front of the engine, under the housing that holds the large upper radiator hose. Two bolts [1/2" socket size] and the smaller bypass hose must be unfastened. This is a good time to replace that short bit of bypass hose with new. Don't break the thermostat housing bolts off - if it requires too much torque, get help from an experienced mechanic. Sometimes, working back and forth with spray lube will remove stubborn fasteners.

Once the fasteners and bypass hose are free, tap the housing loose, and it should come right off, spilling a bit of coolant... unless you cleverly drained some out first at say the radiator drain cock.

Right there in the intake should be your thermostat, easy to pry out. Scrape away the old gasket remnants and put in the new 'stat, sensor end down in the engine of course. Form-a-gasket #2 [NOT SILICONE] makes a great sealer for the gasket AND THE BOLTS, which do pass thru into the coolant.

If you must replace the bolts, use the EXACT SAME LENGTH and/or stainless, so that they won't get rust buildup on the inside, which can prevent successful removal in the future.