I've got a '06 TL with about 130K miles. After a short drive, I left it idle for a bit. My temp was above the mid point on the gauge, roughly the 60% mark from the bottom.
Checked under the hood and both fans were indeed running. Turning on the heater but only lukewarm air was coming out.

Got worried and turned off engine only to see just the passenger fan running. I know that fan are working, but confused at to why temps got to that point where fans were running full speed.


What should I diagnose first? Based on my quick research I should:
- check coolant level
- burp coolant system
- possibly thermostat is failing
- water pump?
- leaks in the coolant system?

 

I'm not very knowledgeable when it comes to cooling problems. I've never had cooling issues with any of my cars so I've never had to go through the rigmarole. What I'm pretty sure of is that the fans will kick on, and adjust speed, based solely on the temps that the coolant sensor is reporting. So they could be spinning like mad - but if there's air in the system, or the water pump wasn't working (or working well enough) you could still see the fans on even when the coolant wasn't necessarily moving so well, or the coolant in the radiator at the time was relatively cool, but just not being delivered to the engine.

I think if I had those symptoms I'd start with a coolant flush and thermostat replacement and see if that helps. Leaks should be relatively easy to spot from the ground. In the unfortunate case that the head gasket is leaking, you should notice some coolant consumption - e.g. reservoir or even radiator running low.

Best of luck.

 

An air pocket in the cooling system could falsely indicate overheating. So yes your first priority is making sure the coolant is at the proper level, not leaking, and properly bled.

 

Did you recently change coolant, open up the system? My first guess is an air pocket due to lukewarm heat when the engine is running hot. I would start by bleeding the system and seeing what happens. If no change, continue moving down your list one by one. I would also check the coolant temp sensor to be sure it's operating within spec.

 

Thanks, i'll have to go step by step in diagnosing this.

Is it possible that the heater control valve is leaking coolant or failing? I've noticed since about a moth ago that the heater would sometimes pump out only lukewarm air.
On certain occasions, I would need to increase the climate control value into the 70s to get any hot air going.

 

No, but I've noticed leaks on the passenger side underside, close to the right wheel well.
Sort of clear not colored, but oily. Always thought that this was the leaking steering rack, but now that I think about it could be coolant.

 

Factory spec coolant is blue and should not be oily. What you're seeing is most likely leaking PS Fluid from the pump or rack.

 

Sure that is not condensate water from AC?

 

That was possibly coolant. My mechanic found that radiator was leaking coolant.
After the radiator replacement it seems to be running just fine.