This happened while in a long road trip (>1000 miles round trip) about halfway through the trip. The engine began to shudder on startup and gave engine codes with a check-engine light. The codes were for misfire, especially cylinder 1, but sometimes 2 and/or 3 (or “multiple”). After replacing the spark plugs and swapping coils, I finally reached the conclusion I had a blown head gasket. I drove the vehicle the remaining 500 miles back home before applying the sealant repair. The coolant level in the main reservoir had gotten considerably low and the exhaust smelled abnormally “sweet” - this confirmed the head gasket leak. The oil in the engine was not contaminated.

Short of engine replacement or a head gasket change, I had to resort to use of a highly rated head leak sealing fluid, which I purchased for under $100. After carefully following the instructions, two heat cycles cured the leak. I made a point of adding the sealant directly into the radiator and NOT putting it into the overflow reservoir. I had to drain two quarts of fluid from the radiator first to make this work. I’m convinced that adding this forte toy to the radiator is important to success. This repair should last for 6 to 18 months and may have to be repeated. This is a known issue with this engine in this model year. I will update if it does mot last.

The engine knocks violently upon start-up, anytime it starts, as the engine stops when the car is stopped or during stop and go traffic (the car is a hybrid, and is on EV-electric vehicle mode at slow speeds or when stopped). The Engine yellow light stays on. I have to fill the coolant reservoir every 100 miles or so of driving.

This is a major defect that Lexus should address and take responsibility for. A Lexus of this type (which retailed for over $ 40,000) should be good for over 200,000 miles (most of my driving has been freeway). I cannot sell this car privately, and I'm afraid that I won't even be able to trade it in for a fair price.

This is reported to be a common problem for both the Lexus CT200h and the Prius of that year, both of which share the same engine.