2006 IS350 @ 106k miles

I noticed that my engine is loosing coolant (about 16 ounces) every 1k mile or so. I checked all the hoses and don't see any leak. However, I see water drop from the top of the secondary water tank (don't know the right terminology for that :-)). The car drives fine and no overheat. The temperature is almost at the middle when the car is warmed up. But I need to drive it for about 1-2 miles for the temperature needle to get to the middle.

The water pump has not been replaced yet.

any suggestion?
Could it be the thermostat?
or
is it time to replace the water pump.

 

I just had mine replaced today, sewell said it was low on coolant and leaking from the bleeder. I never saw any signs of a problem but I got lucky , they replaced mine for free under the power train warranty (06 IS250 65k)

 

Did you replace the water pump?

 

whats the power train warranty??

 

Update:
I took it to my mechanic today and he couldn't find any water pump leak. After 2 hours of troubleshooting, he found the issue.

On top of the coolant reservoir tank, there is a cap and there is a tube that has two hoses, one connect to the engine/coolant tank and the other one goes out to the engine compartment. What he found was the tube connected to the hoses backward. So, it didn't suck the air in, instead, it pumps the coolant from the coolant reservoir tank out.
I'll observe it for a few days and see if this really solved the issue.

 

It's 6 years or 70,000 miles, whichever comes first

http://www.lexus.com/models/IS/warranty/index.html

 

If the coolant isn't leaking out, it is burning off. Have you noticed a drop in overall performance or MPG since this issue arose?

 

No, the car runs smooth and strong. Gas mileage is ok too. I get 26 mpg freeway, 24 mixed. Is that bad?

 

Nope, that's good for a '06. I believe it was your other thread you posted about a grinding noise. Sounds like the pump is going out, and the fins might be rubbing the pump housing. But I'd pull the engine covers and try to narrow down where the noise is coming from first. But yeah, if you'll already be in the engine doing plugs why not go the extra mile and get the pump done too.

I have yet to read of a thermostat going bad in these 350s, but I guess it could happen.