PontiacBonnevilleClub.com

Replacing Thermostats with 160 degree and lowering the radiator cap to 4 pounds may make the intake manifold gaskets last longer. If you look at Rockauto.com and look at an older year of vehicle you will find a Motorad Thermostat 160 degree thermostat that should work.

3800s are either old enough to need lower intake gaskets already or young enough to already have the aluminum framed gaskets. People have ran 180 thermos for years but I wouldn't run the engine cooler than that to avoid extra cam or rod bearing wear from the oil/bearings operating outside of their intended design temp. Also the car will stay in open loop longer.

For the UIM failures, unless the TB flange is warped, all you have to do is fill the TB coolant passages with JB Weld.

Disagree on the 160, that is way too cold.

My car's LIM gaskets were replaced at around 60k miles in 2012. They weren't leaking yet but were definitely rough. Stupidly, I did not replace the UIM at the time. It failed at 66k or so. Second one failed at 170k approximately. We are at 251k now.

The car has been running a 180* thermostat and tune this whole time, but honestly I regret doing it every time winter comes around. The car seems to take a lot longer to produce truly hot heat, and even when it's fully warmed up, it does not feel as hot as my other vehicles. There is also condensation under the oil cap even after a long highway drive.

If you do the aluminum gaskets once, you'll probably never have to do them again. You'll just need to mentally keep track of UIMs and probably do them every 75-100k miles. Even if you plug the coolant ports, the EGR still heavily degrades the area around the stovepipe with enough time and mileage. Luckily it's a super easy job with basic tools.

After GM finished making the 3800 engines, the other engines that replaced them were absolute garbage. In order to keep these engines running as long as possible and keep the Head Gaskets and transmissions from running forever it is wise to keep the engine as cool as possible, but still have headroom in case of a warm day. 160 degree thermostat will run as warm as 170 degrees on a warm day. When you shut off the engine the most it will spike is 199 degrees. Let me explain: 192 degree thermostat on a warm day will be as warm as 202 degrees. The plastic cannot take prolonged 200 degrees temperature and that is why these fail. You shut off the engine and it will spike as much as 235 degrees. The little bit of gas mileage difference isn't going to pay for a replacement intake manifold.