2010 Prius Mileage Going Worse

When your friend drove your car on the same route, what was the fuel efficiency he got in your car?

 

With that many miles and not having been done I'd either get the EGR serviced (if you can find a place that will clean it) or replaced. Not worth the risk of head gasket failure. You are correct that it's not an easy thing to do if you aren't used to working on cars, after I did I wished I had just paid to get it replaced, but then again mine wasn't blocked up at all. I think the choice in tier fuel has something to do with it, I only ever use Tier 1 (Shell/Exxon mainly).

Grab yourself an ODB scanner and download Dr Prius and run the hybrid battery health check. Report back the % life it thinks it has left.

 

With that many miles and EGR never cleaned, head gasket failure is inevitable.

 

IMHO; pay a Prius specialist for a full inspection. Your probably going to have to replace that CAT soon, there's probably a pending code sitting there. Lets face it; it has 190K miles on it - things usually start wearing out or breaking around 150K. That's why car values drops exponentially when they go over 100K miles.
The trip computer isn't all that accurate and you replaced the tires - so they all need to break-in also. You need to give it a few months for the ECU to get used to your driving style, then it'll start kicking out more accurate estimates. Short hops in cold weather isn't going to help your mpgs either. The engine is cold, so it's running rich - burning more fuel. If your friend did the same route with a prewarmed engine; it's already running lean - no cold engine warm-up.
When you make comparisons, you need to make ALL the parameters as close to the same as you can; otherwise the comparison is meaningless.

 

Make sure all four wheels spin freely

 

EGR clogging? I don’t think so, at least not significantly. Until it gets so clogged as to code P0401, when I’ve read it’ll change some running parameters, to try to protect the engine.

 

Congrats on the car! We love our Hybrids....on our 3rd one!

Remember the old-school suggestion of driving like there's an egg between your foot and the gas peddle to get good mileage? Forget that with a hybrid...you need to learn the "pulse and glide" technique. I can get 65 mpg in our Prius and my wife's Corolla Hybrid doing this. (I usually don't, I prefer the bat-out of-hell driving technique also known as the Italian tuneup.)

When you, first, start up the car, push the gas peddle, this will kick on the gas engine (ICE) and help it warm up faster...you want a warm engine to help get better mileage.

Watch this