THERMOSTAT

550 746 45A THERMOSTAT is what keeps your engine's coolant flow in check. Its primary role is to get that big diesel warmed up to its sweet spot operating temperature as efficiently as possible. Once it's there, this little guy opens up, allowing coolant to circulate through the radiator to shed excess heat. It's all about maintaining that narrow temperature window; too cold, and you're burning extra fuel and getting premature wear; too hot, and you're looking at major engine damage.

When one of these starts acting up, you'll usually notice it on the dash. The engine temperature gauge might take an age to climb to operating temperature, or it could be all over the map, especially when the rig is really working hard. A common tell-tale sign is the engine running consistently cooler than it should, which means it’s burning more fuel and not running as efficiently. Or, on the flip side, if it’s sticking closed, you’ll see that temp gauge creeping into the red, and the cooling fan will be screaming its head off more than it ought to, trying to compensate.

Swapping one of these out isn't usually a marathon job, but it's important to get the right temperature rating for your specific engine, not just any old THERMOSTAT. After you've got the new one in, the biggest thing folks sometimes forget is properly bleeding the cooling system. Air pockets in there can cause all sorts of headaches, making a new THERMOSTAT look like it's not doing its job, or worse, still letting the engine run hot. Always give the system a good burp to make sure all the air is out.