Noticed this when the temperature started going down a bit this week. When accelerating in the high away (a bit heavy), my engine temp falls just a bit then goes right back to the middle.
Also I have the air conditioning set so that air from the outside come in and I feel heat that slowly goes away and is replaced by the cool air coming in.

I don't notice anything driving wise, the idle is normal and the driving has not changed. The AC and heat both work. Is this something I should be concerned about?

Thank you in advance for any inputs.

 

Have you had the cooling system worked on recently? If so, time to bleed the system again. If not, you could have a water pump on its way out OR a radiator cap that is failing to work correctly. Lastly, monitor the coolant level in the overflow tank. Are you losing any fluid onto your garage/driveway/parking lot? Perhaps a pinhole radiator or hose leak.

A properly sealing and operating cooling system will show no changes in temp due to how hard you push the motor.

 

^^ +10

Sounds like coolant in the block is low and you have a leak.
If you have a leak, the reservoir tank could be FULL/NORMAL while the engines coolant is actually LOW which explains your situation to a teeeeeeeee!!!!!!!

 

Guys thank you so much!! I know this has taken awhile but I just went to my nearest Toyota Dealership and did a coolant flush and it has gone away. You guys are great, thank you both!

 

NP... ahhw, it was fixed 3months back, yes? Hope so!

 

Glad it was as simple as having some air trapped in the system. Glad you're back to normal and posted about the fix!

 

Sorry I am writing this so late guys. So after about a month and a half of re flushing the coolant the issue came back.
I was so perplexed and angry because I though the issue was fixed once and for all. I was getting sick of diagnosing and taking it back to the shop so that they can try it and give me a "possible" fix.
I pulled the gun and just bought an and .
It has been 4 months now and I can confidently say the issue is gone for good. I rev it to red line on the highway and the temp stays the same.
again sorry for the late update and thank you guys

 

This is just me and I may be mistaken but water pumps are not known for causing this and it is super rare that a thermostat causes it too.

I would bank money on debris caught in the radiator cap (vacuum seal side) not allowing the system to keep the block full and free of air. It happens more than many know.

All of the work done could have easily dislodged it.

Regardless, thanks for reporting and I'm glad it's fixed.

 

Here is a picture of the old thermostat that the dealership sent me.
I'm not sure if its normal but oh well at least I know it was replaced.

 

That's the water pump.

Thermostat below:

 

My bad...confused the two

 

The fact that it was leaking is the point. Any leak *can* prevent the system from refilling when cooling down. As such it was likely low on coolant hence varying temperatures.

You can't have leaks and expect nominal performance.