Hey all...2006 model...186k.
I recently had the fan clutch, radiator, thermostat, and serpentine belt replaced.

Since having it done, half of the days (not consistent) my engine doesn't want to warm up unless I'm driving. (It's been in the 20's and 30's here) For example: If im sitting in a parking lot with it idling, the temp needle only goes quarter of the way up. But if I start driving, then it'll warm up to normal temp and runs great.
Here's the other odd behavior: When it's still not warmed up, the engine fan will kick on HIGH (sounds like a Mack truck) for the first few seconds of acceleration, and then it turns off. During that time, the acceleration is noticeably slower. Once the fan turns off, power feels back to normal.

Is the thermostat they put in faulty? Maybe the new fan clutch faulty? The fan spins with resistance when the engine is off, so I assume the new one should be working properly.
Or...could it be something as simple as air in the system? Or something I'm not considering?
Thanks in advance.

 

Low coolant can cause your symptoms, as will a bad fan clutch.

Were OEM parts used?

 

The coolant reservoir is topped off. So assuming it's full.
Pretty sure they used parts from local autoparts store.
So you think it's maybe fan clutch again, not thermostat?

 

Non OEM parts means can't count on them especially the thermostat. Reservoir can be full but radiator not due to a failing radiator cap. Don't guess! Check (safely).

 

If there wasn't antifreeze in the radiator, wouldn't I be having opposite symptoms? Overheating? However, if the thermostat is stuck open, then I can see having issues like im seeing?

 

Not if there is partial coolant. For example a common symptom of low coolant is poor or no heat in the cabin this is because even though the engine itself will be getting hot there is not enough coolant to transfer the heat. Same thing happens with temperature sensors. Yes if the engine severely overheats then everything gets hot and the gauge needles goes into the red.
Yes it will.

My guess is the aftermarket thermostat is no good, but that's a guess not a diagnosis. A fan that is running on high when it shouldn't doesn't help.

 

My guess is also a bad thermostat.
I don't believe it's possible to install it backwards but it can be installed upside down (there's a port with a jiggle plug in it that has to face upwards)

 

I agree.
I stopped at the shop today, and he said he put in a ‘fail safe’ thermostat, which fails open when they fail. Apparently he’s had several come back lately not functioning properly. My money (and it was my money) is that mine failed too. I told him I want an OEM one, and he said no prob.
Hopefully that’ll fix the issue. It’s prob stuck wide open and engine is struggling to warm up until I’m moving on highway.