Have been to Lexus Dealers three times with no success. Occurs randomly: Start car, sounds like engine knocking, oil low, add oil, noise goes away. Another example: Started car in morning, engine knocked, oil level low, Topped off oil, drove 800 miles, oil levels fine. Can't predict timing. A slow leak somewhere or burning oil. No one can find it. Anyone experience this with their car and have advice or solution ? Please tell me. I've dealt with this for 4 months. ;/

 

The engine knock could be the cold soak issue, read here:
https://www.clublexus.com/forums/ct-...cold-soak.html

Not sure about the oil, if it's leaking somewhere, they should be able to see under the car.

 

The dealers probably don't see a lot of issues like this because they service Lexus models mostly, and this issue sounds like a very rare one. Try a local mechanic with a lot of experience who may have seen the issue, even on other cars. Try repailpal.com to find a good one in your area and get a second opinion.

 

Check if your coolant shows signs of oil contamination which would indicate a head gasket leak. There are tests a shop or dealer can run to check this issue. A leaking head gasket would not show any external oil leaking and may be subtle at this stage. What year is your car and how many miles are on it? Is it still under warranty?

I would go to the www.priuschat.com forum as the CT has the 1.8 Prius engine and they sell a lot more of those than our cars and probably have encountered this issue before. Look at the Prius Gen 3 forums.

 

The same piston ring problem as in Prius is causes oil consumption? What is the manufacturing date of the car?