I took my 2015 300h with 60,000 miles in for routine service and they promptly told me i need 3 coolant system fluids changed in addition to the oil change I came in for. A few days later i had to do a fill in day at a clinic 3 hours from my home where the staff veterinarian had covid and her office was the only clinic in the small town. About 1 - 1 1/2 hour into my commute, the hybrid system over heat light came on. I was on a 2 lane road with no should in the middle of nowhere and could not even pull over for another 20 miles. I googled the error message then checked all the coolant fluid reservoirs and they were full, shut the engine off and since my mpg had significantly dropped, I refueled and drove the rest of the commute with the climate control off. I was in the mid 30's outside. I made it to the clinic, saw patients then started the return trip with no heat on and driving very gently. This time the overheat alert did not come on until 2.5 hours into the trip and going up a steep hill. Again shut car off checked levels and made it home.
The next day I returned to lexus and they said air bubbles in system after fluid change caused over heat and all is fixed now. I specifically asked about battery damage and they said no there would be no issues.
Finally, I get to my question for the brain trust. My prior long term mpg according to the car computer is 42.4mpg. After the last 2 refuelings, each tank has been in the 31 mpg average. All with similar style of driving and same roads and terrain. When the overheat errors happened my mpg on that tankful dropped to 28 mpg. So, what do I do now? Is there a way to test battery function? My wife's hybrid camry had a huge drop in mpg when the battery needed replacing and now I have a 25% drop in fuel efficiency after the dealer messed up his recommended service.
So what say ye?
