The Stant thermostat, fit the existing housing. I took my car to a auto shop, because weather i couldn't work on it. The shop didn't have any issues putting Stant thermostat into OEM housing.

 

Thanks for that

 

I happened to just now see this thread and thought I'd comment on it. My 2000 SL engine temperature behaved quite similarly to the OP's vehicle many years ago. My thermostat would get slightly above the 1/4 mark on the temperature gauge and stay there after warm up. I would have to crank my heater all the way to the right to get any decent amount of heat in the winter. I finally put in a Stant thermostat probably close to 10 years ago or so, and the temperature now reads as in post #19 above (3/8 on the gauge or slightly higher). That is exactly where it should be, and now the heater is blazing hot when cranked all the way after the engine is fully warmed up. Stant thermostats work well (and my experience indicates that they seem to last a long time also), so I highly recommend using one in your old Saturn S-series if you can find one. I can actually watch the temp gauge go up and down once the car is fully warmed up as the thermostat cycles back and forth allowing maximum coolant flow through the radiator and subsequently reducing the coolant flow through the radiator.

 

Thanks for that report!