Do thermostats have a break in period?

[demian5]

When replacing thermostats here is what you should do.

After replacement and topping off the fluid, turn on the heater so the heater valve is open and run the engine with the cap off for about 5 minutes and top off the fluid. I like to run at about 2000 RPM and hold for about a minute to get air out. Top off fluid and put cap on, and top off the reservoir (if equipped).

I put a large fender cover over the grille to prevent air from going through radiator for cooling so this goes faster.

Run vehicle and hold at about 2000-2500 while watching temp gauge, on newer cars, connect a scan tool and monitor the ECT sensor temp. Let idle here and there and raise engine RPM back up until the temp gauge goes up. With a new t stat sometimes the gauge or reading goes higher than normal the first cycle, but stick with it until the thermostat opens.

When the thermostat opens you will see gauge drop a bit or temp go down, run the engine for a couple more minutes at idle then shut it down. I like to confirm temp with a temp gun as well so i know what the gauge reading is at.

After the engine cools, check the coolant level in the cooling system (radiator or expansion tank) and top off the reservoir.

Some vehicles have a coolant bleed port that needs to be opened when filling the engine with coolant, or some vehicles like to have the front of the vehicle jacked up. The goal is to get the air out of the system. This is usually accomplished by having the filler part of the cooling system (radiator cap) higher than any other component in the cooling system.

[Mike72gmc]

On some vehicles, make sure that when bleeding the cooling system that the heat is turned on. Some vehicles have a valve that restricts or stops water flow through the heater core. Not necessarily needed in this case but as a general rule of thumb so that the whole cooling system has the air flushed out. Air in a cooling system is bad. Last note, use radiator shrouds as they force the air through the radiator rather then recycle air around the engine compartment.