Dsouth1995

Bought my ES350 2007 (low mileage- ~80,000) a couple months ago. Drove it halfway across country once and haven’t noticed any problems. Now the car overheats after 6 miles - throws engine light and VSC. Mechanics found black gunk in coolant after it was flushed. The thermostat was replaced but it didn’t solve the issue. Apparently water pump runs hot water through the cold water line and vice versa (also was gurgling). Want to know if this is a problem with the radiator, water pump, blown head gasket, etc.

Clutchless

That is odd looking coolant for only 80,000 miles. I have changed it at 100,000 and it looked almost new on Toyotas.

You may need a new radiator and a new water pump. Water pumps are a known failure item on this engine. Usually you can tell from the noise if it is bad.
You may need to see other mechanics for a second opinion. Use Google and Yelp to find some good shops.

They should be able to look into the radiator and see if it is clogged and needs to be professionally cleaned out or replaced.

Have they done further test to rule out a bad head gasket? Does your oil look muddy or murky which indicates coolant leaking into the oil from a bad head gasket?

spaceballs

Also, check if you have a coolant leak outside the engine near the head gasket. With time the black material on the head gasket wears down and rust from outside can eat in, causing a head gasket leak but not into the piston.

I have a feeling that there may have been a coolant leak before and the previous owner put in some stop leak, that's finally stopped working, that may be what your black gunk is.

Clutchless

The leak evidence is dried pink coolant residue usually on the rear side of the engine block, facing the rear of the engine bay. You may need to pull off the plastic engine cover and get a flashlight and mirror to see back there. The engine cover just pulls off, there are 4 pins that it presses into.
If on the front side it is easier to spot.

Oro

I can’t see any pics (someone else mentioned them or sounded like it). Is there any chance dexCool could have been added to this car?

Because if so it will gel and clog the radiator. Spaceballs may be right about an additive being introduced.

Cooling system problems are really NOT hard to figure out when you know how the system really works. Mechanics should have told you what’s going on. 6 min to overheat sounds like stuck thermostat or it is a very clogged radiator and/or engine cooling journals. Either will create pressure on one side of the system and you will get spray out of joints. That spray will then leave pink crystals on engine parts or accessories. Don’t be fooled by that. It’s a by-product but not the cause.