by Hib Halverson
A common modification for a ’16-’19 CTS-V’s LT4 is a change from the stock, 194° thermostat to lower temperature unit. A good choice for a high-performance street application is a Weapon-X 180° thermostat (PN SD180LT1). The goal with that change would be to lower engine coolant temperature (ECT) during highway driving as well as during aggressive driving at higher speeds.
On an LT4, a ‘stat change is pretty easy. You drain the radiator, close the drain then remove engine cover. Disconnect the upper radiator hose and the steam hose that runs between the thermostat housing and surge tank. Then remove the three housing bolts and pull out the ‘stat.
The housing and the thermostat assembly are all one part. The thermostat “core” is part of this assembly. Grasp the housing in one hand and then push the other end of the assembly against spring pressure and twist the bottom metal cap. The cap will come off. The springs will come out. Then, the thermostat core can be extracted from the housing.
Put the Weapon-X 180 in place of the OE thermostat core. Put the springs back in place. Then push, twist and lock the bottom cap. Install the thermostat assembly back into the the engine, install and hand tighten the three housing bolts. Torque each bolt to 10-Newton-Meters or 89-inch-pounds. Finally, reconnect hoses, reinstall clamps and put the engine cover back in place.
Now you’re going to refill the cooling system with whatever water/antifreeze coolant mix you choose. Double check the radiator drain closed, fill the system until the coolant level gets to the bottom of the surge tank fill neck. Start the engine and idle it for about four minutes while adding additional coolant to keep the coolant at that level. Next, run the engine at about 2000-RPM for a couple of minutes, then let the engine idle and check the coolant level, again. Add coolant as necessary then shut the engine off. Let the engine cool to ambient temperature–usually I let the car sit over night. Check the coolant level and adjust as necessary then reinstall the surge tank cap.
We’ve had Weapon-X’s 180 ‘stat installed for a couple of months now. There were no problems installing it. No problems with leaks and, on the highway, the ECT is 180-183°. I have not run the car on a chassis dyno with the 180 installed, yet, but in driving where I’m running the engine harder than I would just cruising on the highway, the ECT is lower than it was in similar situation with the stock thermostat. The cost of the part was 60 bucks which is a lot less expensive that some alternatives which consist of the whole assembly rather than just the thermostat core by itself. The Weapon-X 180 is also 10 bucks less than Katech’s thermostat cores.
Weapon-X also sells a 160° version of this thermostat. For more information, see the Weapon-X web site.