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Engine is designed to run at ~ 190. I don’t know what cutoff is, but pcm will not change from open/closed loop, until it reaches temp. If it doesnt (or until it does), it will not be running at optimal efficiency (ie crappier mpg).
so although there is no catastrophic risk (that I know of) by running cooler than design, it isn’t ideal.
I don’t have an infrared yet but I can tell you that I just let the ECT get as warm as it will go, still 176. I monitored the entire time and the fan jumped back and forth from lower to higher speed the entire time. I turned vents from full heat to full ac, defrost to vents to floor, and the fan never changed. Steady faster slower faster slower, about 15-20 seconds each cycle. The upper radiator hose is very hot, the lower is completely cool. It’s currently 46 degrees outside. As many times as I’ve tried purging an air pocket, inclined, squeezing the radiator hose, I feel fairly confident it’s not that.
I don’t have an infrared yet but I can tell you that I just let the ECT get as warm as it will go, still 176.
Originally Posted by getterdun
Does your OBD tool show CHT?
The truck's computer has a reading for cylinder head temp and engine coolant temp. The truck only has a cylinder head temp sensor. The engine coolant temperature is inferred, from the cylinder head temp sensor, and readings from other sensors. Compare the two readings. Cylinder head temperature should always be higher than engine coolant temperature.
Originally Posted by aut192
I monitored the entire time and the fan jumped back and forth from lower to higher speed the entire time.
What you now know is that the fan clutch and fan are working. The fan clutch is supposed to engage when air temperature around the fan clutch is around 200. I've also heard that number could be 205. Don't worry about the exact temp. The important thing is that the fan clutch is fine. That's the temperature in the air, which changes with airflow through the grille, and obviously if the hood is open.
Originally Posted by aut192
I turned vents from full heat to full ac, defrost to vents to floor, and the fan never changed. Steady faster slower faster slower, about 15-20 seconds each cycle.
You have a mechanical fan. It reacts to air temperature, much the same way your thermostat reacts to coolant temperature. With aftermarket electric fans, and OEM electric fans, turning on the HVAC will trigger fan operation. Your truck will not do that.
Originally Posted by aut192
The upper radiator hose is very hot, the lower is completely cool.
Assuming that you have a brand new, working, 190 degree thermostat, it's open and not stuck closed. This also allows us to presume that the water pump is moving coolant, so that is working. And we know that the cooling system is working as designed, since the fan does spin, the fan clutch engages, and you have a hot cooling hose with a cool return hose.
Originally Posted by aut192
It’s currently 46 degrees outside.
This is a screenshot from my car, taken today.
The ambient air temperature was 52.
The intake air temperature was 84.
Driving at 7 miles per hour.
Fan off.
Engine Coolant Temperature was 174.
I'm not worried. This is normal.
Originally Posted by aut192
As many times as I’ve tried purging an air pocket, inclined, squeezing the radiator hose, I feel fairly confident it’s not that.
You do not have an air pocket. An air pocket causes overheating, and no heat in the cabin.
The only thing left for you to confirm is the cylinder head temp vs coolant temp readings, with a thermometer. The mechanical parts of your cooling system are operating as designed. You could do a little more research and learn about the cylinder head temp sensor. Maybe even wonder if it's working correctly, or if the harness is corroded which causes bad signals.
I wouldn't worry about "overcooling" in the winter. Other people have had this concern in the past. I don't think anything ever came of it.
Last edited by Chinatown Boy; Feb 1, 2024 at 10:59 PM.
There's a lot of information about open and closed loop system operations. A search on the web will confuse you more.
Without needing to understand it, I can set up the ScanGauge II to show open loop and closed loop. I suspect that better quality code readers will allow this display as well.
Scan tool says ECT stays right around 174-176 at all times.
The bigger picture is that your truck is not overheating, the heater and air conditioning work, and that all of the mechanical components are functioning as designed. You will be fine.
Here's what my truck looked like today, just before lunch.
The bigger picture is that your truck is not overheating, the heater and air conditioning work, and that all of the mechanical components are functioning as designed. You will be fine.
Here's what my truck looked like today, just before lunch.
Ambient temperature at 53.
Speed of 40 mph.
Fans are off.
Engine coolant temp is 173.
I think most will agree that running cool is better than overheating. But the goal / proper temp for these should be maintaining ~ 190*. If you are unable to reach and maintain that (and didn’t intentionally mod for some other temp), then something isn’t working as designed.
Snap shot of temp without knowing other details (examples: if warmed up or not, or what tstat is installed) doesn’t mean much on its own.
Open vs. closed loop
