Q: With the recent warmer weather, I’ve noticed my pickup will sometimes run hotter than I think it should. I’m wondering if changing the thermostat to a colder one would help. T. Rumsfeld
A: Assuming the cooling system is full of coolant (a 50/50 mix of antifreeze and water is preferred), leak free and you’re seeing an occasionally high gauge reading, let’s start by qualifying the temperature gauge readings. A neat way to do this is with a non-contact digital thermometer, also called a temp gun. These are now widely available and the cheapie ones have dipped below $20. This tool has many applications one can check brake temperature, air conditioning /heater output, catalytic converter function, engine or transmission temperature, your refrigerator/ freezer’s settings there are endless possibilities!
You can check true engine coolant temperature by aiming the gun at the engine’s thermostat housing. If you find the truck’s gauge and the gun agree, when at normal and elevated temperature, we’ll go from there. The truck’s thermostat is designed to maintain engine coolant (overall engine) temperature at approximately 195 degrees F. At startup, the thermostat is closed, blocking coolant flow through the radiator, encouraging the engine to warm up as quickly as possible. As coolant temperature reaches 195, the thermostat opens, and continuously meters flow through the radiator to maintain this temperature. Should conditions cause elevated temperatures, the thermostat opens fully, allowing maximum radiator participation. As long as the thermostat is functioning correctly (opening as it should), it plays no role in managing temperature above 200 degrees or so.
If there’s any doubt the thermostat is working properly, I’d change it in a heartbeat, with one of the specified rating. They’re inexpensive, and it’s typically a simple job. Changing to a colder value (180 or 160 degrees) may briefly assist a weak cooling system when one encounters a single steep hill (you’re starting out cooler), but the drawbacks are many. Your engine was designed to run best, produce the fewest emissions and deliver the best fuel economy at 195 degrees, in addition to the oil remaining cleaner compared to running at colder temperatures.
Occasional elevated temperatures may be caused by a partially restricted radiator, airflow across the radiator impeded by bugs or debris, an eroded water pump impeller, collapsing lower radiator hose or a slipping fan clutch. Radiator efficiency can be checked using the heat gun, comparing upper and lower radiator hose temperature when at operating temperature (thermostat open). With adequate airflow across the radiator, you should see a difference of over 20 degrees. If desired, a heavy duty (thicker, more passages) radiator can be purchased for less than $200. Replacement could be a satisfying DIY Saturday job renew all hoses at this time as well. If the temperature drop across the radiator looks OK, but the inlet temperature (top hose) is notably higher than the thermostat rating, the water pump may not be providing adequate coolant circulation. For fan clutch information and testing, go to www.haydenauto.com, click training, and fan clutch tutorials. They did a nice job on this.
E-mail Brad Bergholdt at under-the-hood@earthlink.net.
