I've had no issues with the temp going up or any other engine problems.. any experience with this? Is there a way to diagnose/replace myself without getting raped in the shop? Please let me know if you've had any experience with this. Thanks!

 

What is the code?

 

Take the thermostat out and submerge it in a fluid of known temperature. Watch it opens / closes.
This is written in the shop manual.

But just replace it because the thermostat is only $30.
Testing the existing one will cost you more time and money....

 

You can buy thermostat at local parts store for $10 - $12

 

But you shouldn't.

 

People like you keep dealerships in business

 

As a GENERL rule, OE parts, are far superior in every respect over aftermarket parts.

Buying an aftermarket thermostat is totally false economy.

 

You want dealerships to go under?
Exactly.

 

As suggested replace the thermostat. Alhough you did not provide the code most likely it was because it did not reach operating temperature in the proper timeframe. In other words it's getting lazy!

 

For real? I didn't realize that, sorry man. (being sarcastic here)
Actually aftermarket parts have to meet or exceed OEM ratings, most decent brands do that. I certainly do NOT suggest buying a Fram oil filter for your Lexus but you will have great results with Napa Gold or Wix as these parts meet or exceed oem quality specifications.

If you get your car into bodyshop, do you ask them if they can buy paint from Lexus?

 

That's not really the right thread for this side debate, but OEM, OE, and aftermarket parts are not the same thing at all. You are confusing totally different things.

 

I'd buy a Fram. As far as I know, no one can produce any scientific testing that says Fram filters do not do the job they claim to do: meet the engine manufacturer's specifications for full flow oil filters.

 

Lexus OEM oil filters cost well less than $10. Why take any risks whatsoever for a few bucks every 5000 miles? Makes no sense to me!

 

This post has now totally deviated from the OP's problem and topic,

 

The thermostat, and cooling system are also part of the fuel system in that the PCM uses the input from one of the coolant temperature sensors to adjust the fuel/air mixture. You should stick with OEM components for the fuel (system) , and also the cooling (system) since they both need to be accurate. If you get the Toyota part number for an OEM replacement thermostat and o-ring gasket, you can purchase the OEM Toyota components on ebay.com, or amazon.com for less than the dealer would charge. Some Toyota/Lexus dealerships sell components on ebay for a reduced cost.