Took my 2008 4.4 on a short trip today and the truck did not come up to temp. About 36F ambient, 25 min of city driving and it just came up off cold a little bit. The cooling fan was roaring the whole time. When I parked I spun the fan and the clutch felt pretty stiff. Seems like time for a new fan assembly?

Other data points:

• Battery is strong. I did have the fan roaring in the summer back in 2017 at 136k miles when the alternator failed. Currently at 170k, so the reman Denso alternator has 34k miles and a little under 6 years of age.
• I had to top up coolant about an inch or two on the overflow reservoir recently, which was unusual, but it's been probably 20-30k miles since I even looked at it.

Also, found some forum hits about a relay issue causing the fan to run constantly, anyone have details on that? I'd like to do due diligence on troubleshooting but seems like the stiff fan clutch is a strong indicator and I would think 170k is a decent life for a fan.

Cheers,
-Dan

 

I don't have any experience related to your question Dan, but since the water pump is in my near future, seems like I should go ahead and replace the fan too.

Side thought, doesn't the thermostat allow fluid into the radiator for it to be cooled? So even if the fan were going, if the fluid isn't up to temp, it should be held in the engine block if the thermostat isn't stuck open?

 

Great point. Although not sure why a stuck open thermostat would cause the fan to run.

I did a quick check in the driveway today. Cold start with IIDTool running. Fan RPM and PWM signals were doing reasonable things, and the fan slowed down after ~30s like normal.

Will drive a longer trip later and see what happens.

 

10-4, let us know. My thought on the stuck thermostat was more to address the coolant temperature barely coming up off of cold when 25+ minutes of driving. I know my LR3 will get to operating temp, north of freezing temperatures within 5 minutes or less. I'll be interested in hearing what others might have to say as well.

 

Update: Took a couple of additional short trips and one longer one. Everything just absolutely normal. My theory is that for some reason at startup (the one time), the fan and ECUs lost comms and the fan defaulted into max demand. There was enough cooling need to open the thermostat, but with cool ambient temps and the fan maxed out the engine couldn't come up to operating temp. Maybe?

Anyway, that's best I got for now.

 

Thing to know about the cooling fan:

If unplugged it will run full speed, this is because by default (no power) the clutch is fully engaged. Power is what actually throttles it back to slow it down and disengage the clutch.
If the power management suspects a charging issue, the fan is the first to get cut since it can draw a lot.
If you clear engine codes when running, you can often get a false temperature sensor fault. That will cause the fan to run at full speed since the engine can not trust the sensor. It assumes the engine is hot.
If the engine is running too cold, the fan can in fact run at full speed. This is to make the engine work harder and heat up. You would think the increased airflow would cause things to cool down, but remember the cooling fan is moving air over the radiator and has less an impact on the engine itself where the coolant is more or less is a closed system separate from the radiator. So with a cold engine, fan running full the coolant inside the engine should heat up until the t-stat opens and starts to regulate as needed.

 

Can vouch for this one! I did that once and the fan ran continuously until I shut off the vehicle and restarted. When checking codes I had the P0116 code (Engine coolant temp signal failure). Lesson learned —don’t clear codes with the vehicle on.

 

Thanks gents. Didn't clear codes while running this time, but seems clear that it was some sort of momentary fan speed sensor fault.

 

A continuously running fan is also a sign of a bad alternator.
Not saying that's your problem, but it could be.

The thought is the alternator produces a dirty signal, that confuses the HVAC control system, which turns the fan on and off. If the fan stays on continuously, it may be because the HVAC controller is telling it to stay on.
You might want to double check your alternator.

JeffGeneral disclaimer: I might be wrong

 

On a lot of makers if the ECU looses comms with the coolant temp sensor it'll default to full fan speed to protect from overheating. Not sure if the LR3 motor is the same, but we literally just had this happen on a C7 Corvette.