I have had the Rx 450 h for about 4 years and love it. One of the surprises was that I usually got between 26-28 MPG It would typically average 27 on long trips on the freeways. I recently had the 125,000 mile recommended maintenance done where the installed new spark plugs, and some belts and other things. Lots of money for what they did. In addition, they installed a new set of he same style Michelin tires that I was running and but new rotors' and brake pads on the front.

I left the dealership, and drove about 45 miles home. On they way i got gas and noticed that the gas mileage on the trip home was 24, where the previous tank was 27-28 combined city and highway. I usually would get 26-28 MPG on the highway consistently at freeway speeds. Thinking this was bad gas, I waited for an extended trip which I am on now. The gas mileage has been consistently at the 23-24 MPG level. Which is a good 3-4 MPG less than I got before service. I typically run the car in Eco mode on the dry highway pavement.

I called the service manager at the Lexus dealership and he said it could not be caused by anything that they did. I do not believe in coincidence here and wanted to know what others experience was. I asked him about the spark plugs that were installed. He said that the ones that were installed were the ones that their parts catalogue says should be installed. I did not ask if the ones that were installed were the same as the original equipment when the car was new.

I am going to have another conversation with the service manager and wanted to ask the forum for any ideas that may have been overlooked.

Thank you in advance for your help,

Jim

 

Jim, this may be related to refineries switching to the winter gasoline mix, which will decrease gas mileage. And your service trip just happened to coincide with this change.
New tires will also have slightly more tread and more friction, further reducing the gas mileage. Check the tire pressure to make sure it is set correctly.

 

And Mother Nature just switched off the heat here in Michigan, too! But assuming the OP has driven the prior 125K miles here, he already knows that issue).

Perhaps a member of this message board with service experience with the plug-change process could shed any light as to whether or not a computer reset or other history-losing procedure occurs with that process ( thereby requiring the computer to re-learn things )?

I wouldn’t be surprised (wishful thinking, actually) that at some point in the diagnostic process that a software adjustment would be performed to adjust traction battery performance/maintenance - for the objective of prolonging the traction battery’s useful life. (Say it is so, Toyota.)