I have a 2011 LS460L with 114k miles. Everything has been great until driving to the airport the other morning cruising on the freeway and it dings saying it’s overheating, I look at the needle and s**t! It’s in the red. I immediately start pulling over and all of the sudden the needle drops to normal in 2 seconds. It was about 60° outside and earlier I turned the heater on and it worked fine, then maybe 20 min later it’s blowing cold air. I didn’t think too much about it besides I’ll mess with it later. Then the overheating happened. Once temp dropped back to normal… I tested the heater and it worked fine and the car stayed normal temp the rest of the trip. Coming back, the needle creeped up to 3/4 of the way, I throw on my signal thinking here we go again, and then drops. Doesn’t raise once the last hour and a half drive. I’m thinking thermostat but someone else said maybe sensor. I want to drive more to investigate but I don’t want to screw it up.

 

Did the thought to check the antifreeze ever cross your mind?

 

This is a great way to permanently damage your engine. You are low on coolant likely a leaking radiator but can be other components like a leaky water pump. Open the hood and look for pink deposits/residue (assuming your car has the proper coolant).

 

Ain't got no coolaid in it!

My bet is the rad and or valley plate

 

yes it’s full

 

coolant is full and no signs of leakage.

 

Check that the water pump is moving coolant consistently

 

Inconsistent heat almost always means low coolant, sans some sort of electrical failure. Coolant in the reservoir doesn't mean there is enough coolant in the system.

 

Check both engines' cooling fan motors, there is a TSB for that.

If both engine cooling fan motors check out, then check the engine coolant temperature sensor.

 

Cooling fans don’t do much when driving at highway speeds.

 

I just had this issue I had the valley plate leak repaired on my car back in February and this same thing just happened last month; Problem was air in the system waited until next morning removed coolant cap filled up reservoir cranked engine let it run with cap off it started bubbling waited until bubbles stopped problem solved. Hope this helps.