Sudden Drop in MPG

They may have overfilled your oil. Check your levels.

 

I'd agree, check the oil level but, most likely, they reduced the pressure in your tires. My dealership does that to me every time, I keep it at 44/42 and invariably after a servicing they are at 35/35.

 

Was this dealer service that did the oil change, or somewhere else?

If the counter has not been reset, then you will have an indicated mileage hit from the engine being operated without being driven (during service.)

Check oil level--Toyota's official procedure calls for too much oil. They might also have used higher viscosity oil.

Tire pressure is of course the most likely culprit if it isn't just a result of fuel burned idling while being serviced.

One other thing, check your A/C settings. The tech might have changed blower or temp settings on you for his/her own comfort. If the defrost is running and/or the blower is blasting then your ICE will run more frequently and that will cost you mileage.

 

I've had the same problem before, they over tightened the rear brakes. They would barely spin on there own, Dealer loosened them a bit and mileage went back up.

 

This has nothing to do with a service, but

I was getting over 50 mpg avg. until last week. Was 55ish, went closer to 52 with more short trips, then ...

refilled with gas, we had some overnight freezing temps and a few storms ...

the car has settled into about 46 mpg now. Some long trips, medium and short.

Cold temps, winter blend fuel (?), shorter trips, running defogger more, all takes its toll.

 

What state are you in? In California, we just switched to "winter blend" gasoline which reduces pollution but gives worse mileage (typically 10-20%:frusty.

 

I've had the same thing happen to me. You might wish to read the thread I started entitled, "After Service Issue" which outlines the cause and solution of the problem for me.

 

I see a drop when it gets cold.....weather changes