Did some searching but didn't find anything - I'm wondering if there's a DIY for replacing the coolant (& thermostat too) for an ES300 on this forum somewhere?

Really if you want to do a flush I would take to dealer, I know I hate the daeler ( Toyota dealer not lexus )too but when it comes to coolant and trans flushes those are the only two things I would ever take to a dealer bc they have really good machines that completely flushes every thing out and it is done properelly better then drain and refills which we could do on our own, and I have the Lexus pdf manuel for therm replacement if you want kinda had trouble sending a pdf to other ppl I just cant figure it out but if you know how i could send you a factory guide to relpacing that if you want

yea the suction method is better, but not something that you could do on your own, pretty sure jiffy lube offers rad flushed for like 60$

Oh BS. Jiffy lube? Seriously? I wouldn't let those hacks change the water in my birdbath.

Replacing the coolant is easy. You can get almost all of the old stuff out by first draining the radiator, then open the block drains. Do yourself a favor, stop at the local hardware store and get some clear plastic tubing, 1/4" ID works fine, maybe a foot or so. Stick it over the nipple on the block drain, this will let you run the drain into your drain pan and you won't get coolant splashed all over the place.

Be sure to put the old coolant away quickly, don't let the open pan sit around where an animal might drink it. They love the taste, but it's a very painful death.

Only use Toyota red coolant, mixed 50/50 with DISTILLED water.

why coolant flush? if not done properly may result in air lock/overheating problems. it may be better to do a drain/fill a few times than the normal change frequency.

Coolant flush is not necessary. I've been draining and filling my cooling system for years with no problem. My 94 ES 300 has over 300k miles on it and still going strong. Do use OEM thermostat and fluids though. Definitely, stay away from Jiffy lube or similar chains.

A coolant flush can easily be done yourself, you just have to have a few basic things. One is you will need wheel ramps, or at the very least, a good floor jack and quality, safe jack stands. You will also need one of these. No exceptions, without it, you will have a difficult time removing the air, and will waste coolant as it spills when bleeding out the air.

Things you will need. Spill free funnel, 9 liters of Toyota red or pink coolant. The red needs to be mixed, so buy half of the total you need. 12-14 liters of distilled or deionized water. Appropriate drain pans, a container to mix coolant with water if you use Toyota red. And of course you need a few basic tools.

1. Make sure the heater control is set to maximum before you start. The hose that goes to the overflow tank, remove the tank side and plug the hose with a socket extension or large screwdriver.
   
   
2. Drive the car up on the ramps, or safely lift the car and place on jackstands. Make sure the car has cooled off somewhat before you drain the coolant. Loosen the radiator drain plug and drain the radiator. After some of the fluid drains out, you can go ahead and remove the radiator cap to speed things up. NEVER REMOVE WHEN HOT!
   
   
3. There are two drain plugs on the block, one of the front, one on the back. Drain the coolant from both, the back one is a bit hard to remove, use an extension on a socket to get to it. Be gentle when loosening the back drain, it is made from delicate aluminum and can strip fairly easily.
   
   
4. Install your funnel onto the filler neck. Tighten all the drains up temporarily, and proceed to SLOWLY fill the engine with 100% water (NOT TAP WATER!). When you have about 3-4 liters poured in, stop, and run the engine for 15 seconds then shut it off. Fill the rest to the top, then start the car and let it warm up to operating temperature. Top off the funnel as needed. At this stage, you could add in some radiator flush if you have deposits that need to be removed. I have not used such a product in years so I can't recommend a good one. But always follow the directions on the container
   
   
5. Drain the water out of the system like you did before, make sure the engine cools down enough so you don't burn yourself. Tighten the drains back up, put some anti-seize compound on the rear drain plug threads while you're at it. Fill the system slowly as before with your coolant that you either mixed yourself from the Toyota red or the pink, but this time start the engine several times for 15 seconds as you fill in steps. This minimizes the amount of air that gets into the system.
   
   
6. Run the engine with the funnel filled several inches. Make sure the funnel always has coolant in it. As the engine runs, you will see the air coming out of the system. The reason you have the funnel is because it allows for expansion without spilling, and does not allow air to get in. Rev the engine up and down occasionally, and just wait. It can take a long time for all the air to come out. It can sometimes help to stop the engine for 5 minutes then start it up again to remove trapped air. You know you're done when you see almost no bubbles rising out of the funnel.
   
   
7. Put the plug into the funnel, and remove it. Put on the radiator cap, put the hose back onto the overflow tank, and fill the tank almost to the top. The system will draw coolant into the engine as it cools down, so this level will drop. Check the tank again for several days to make sure the level is near or at the top line when the engine cold.

A few notes. A 50/50 mix is good for moderate to cool climates. For areas that get very cold, use 60% coolant. About 67% is the absolute maximum, after that point you get no additional freeze protection, in fact the freeze protection gets worse. Don't use less than 50% coolant or you will have poor corrosion protection. When flushing with water, keep in mind that you will never be able to drain all the water out of the system, some will remain. So when mixing yourself, compensate for this. The Toyota pink is 60/40 at the dealer here (it may be different in other climates) so that should be enough to compensate for the water left in the cooling system. If using Toyota red, you can just fill the overflow with 100% coolant. A hydrometer is helpful if you're really paranoid about getting the mix perfect.

Thanks guys!

Can anyone tell me where the thermostat is located?

Nice write up, Lexus2000.

whats with the jiffy lube hate lol, ive had my rad flush done there a few times on a few different cars and never had a problem, i guess it depends on what location you go to