2010 Prius’s mileage going South

Winter will lower mpg because of the cooler temps, and the ICE engine will have to run longer
to warm up and also to provide heat, when heater is in use.

However PA winter temps have been unusually warm from previous winters, so my mpg has really
not gone down that much.

Yes, you should look into the egr, but this would be for DIY as a dealer would only accept monies
to replace it verses cleaning it. Cleaning it would be just be the cost of time and you doing the work.
Replacing it? I really dont want to know the cost but maybe $1k (then also add in other things they want to do)

Other things....

HV battery. If it is in bad health and going south, so will your mpg.
Tires. while should not decrease mpg that much, could be combination adding to the drop.
Engine Oil. You check frequently?
12v battery. You said you changed it, was it with oem, or ? could be that time to check or change it again.
Brakes. could be pads dragging, or ebrake dragging needing adjustment.

Do you DIY, can you DIY
Any dash lights?
Are you able to read codes with scan gauge, dr prius app, hybrid assistant app, hybrid code reader?
Might be worth getting one of those to not have to bow down to the dealer and sell your soul to them.

 

Is it 130k now?

There are so many things that can affect mpg’s, read thru some threads, and definitely do the egr circuit before your engine blows.

Is she burning any oil?

 

I do the maintenance on my 2010 prius and I replaced the plugs with Denso about a year ago and the mileage shot back up to upper 40's, but it didn't last long. About a week ago the engine started to skip a little here and there, then the dreaded check engine light. I immediately ruled out plugs because only 15,000 on them. I pulled them and they looked good, but the gap were at 60 thousandth !!! Put new plugs in this morning and it purrs like a kitten and the mpg is back !!!

 

Unless it’s a right side driver prius, it’s physically impossible to pull the plugs with the cowel still intact. In that situation, I would ask for the used plugs to be in my hands before I leave the stealership. If there were more than 1 person simultaneously working on the car then it’s possible they had it done within that time period.

 

Removing the wiper assembly was easy. I watched the video, and followed it step by step.
Going back to the passenger seat to watch the next step. I have the assembly removed in less than 10 minutes.
Replacing the plugs is a 5 minute job, at most. Reinstall the wiper assembly, 10 minutes.

When I did the egr cleaning, I had it off in 5 minutes, without looking at the video.
So an hour is easily doable.

 

If you get an OBDII bluetooth adapter that you plug into the diagnostic port under the dashboard, you can then run the Dr Prius app that will tell you whether the hybrid battery is operating properly and an estimate of battery capacity.

 

How long ago did you change your 12v battery? It is not unusual to experience lower fuel economy for a couple of weeks after disconnecting the 12v. After driving around for a while, the computer re-learns your driving style and adjusts.

 

Maybe si, maybe no, but seriously, what are you saying? Are you sharing useful information? Or just crowing...

The typicaly DIY'r will take a lot longer than that.

 

No maybe about it. It IS super easy. It looks like a lot of work, but it's not.
I was replying to Norryboy1a. Someone at the dealership who has R&R'd the wiper assembly
and replace the plugs many times, can do it fast. That's why it tool less than an hour. Maybe a 30 minute job from start to finish.
I would guess that is the time the service writer did his/her thing, the tech got the paperwork, got the car,
pulled it in the bay, went to the part department, got the part, back to the bay, did the work, wrote up the
work order, turned it in, test drove the car and returned it to the parking spot, customer went to the payment
window, paid the bill, got the key, and went to his car.
An hour.....

I don't "crow". It doesn't help anyone.
I am only stating how long it took ME to do it.
Soooooooo.... ONE MORE TIME....

RESULTS MAY VERY!

 

I have a 2014, but I really haven't seen any difference in mileage going south versus going north.

 

How many miles?

 

Yeah better get busy with the EGR and intake manifold cleaning. It's getting late-in-the-day, better sooner, say around 100K. A free flowing EGR is mandatory to keep engine temps down, it's one of the reasons for it. Someone may be along soon, to explain that in the absence of scientific measurement, there's no point in saying this. Anyhoo:

The simplest way to see where you're at, is to check the degree of carbon build up in the EGR pipe, a stainless steel connecting pipe between the EGR valve and intake manifold. Watch @NutzAboutBolts video #16 here:

Nutz About Bolts Prius Maintenance Videos | PriusChat

Two or three other videos linked there too, for the full cleaning of the intake manifold, full EGR clean, and Oil Catch Can install.

Good thread:

EGR & Intake Manifold Clean Results | PriusChat

Another:

Oil Catch Can, Eliminate that knock! | PriusChat

Some tools worth having:

E8 Torx socket (mandatory)
E6 Torx socket (optional, but good to have, to remove the throttle body studs from intake manifold)
3/8" ratchet wrench, regular and long handle, flex head, you can never have enough (or 1/2 plus reducer)
1/4" ratchet wrench, or 3/8" to 1/4" reducer
Ratchet extensions: you can never have enough
Long needle nose piers, straight and bent tip
Ratcheting 12mm box wrench (optional, but makes disconnection of the EGR cooler from exhaust easier)
Torque wrench (3/8" and 1/4" both good to have)
Floor jack and safety stands (or ramps): basically some method to raise front, if you need to take underpanel off, which you may need to, both for access and to recover dropped items.

Comment regarding clamping of coolant hose, mentioned and or shown in videos:

1. When removing the intake manifold for cleaning, you do need to lift the throttle body off the intake manifold. Still, the coolant hoses connected to the throttle body have ample slack, enough that you can leave them connected, and just tie the throttle body to something adjacent, say the inverter wiring harness.

2. When removing the EGR cooler, removing coolant hoses is necessary, but if you drain 2 liters/quarts from the radiator drain spigot prior (into a clean container), the coolant level in the system will be dropped below the EGR componennts, and you won't spill anything. Just be sure to not tip the cooler when lifting it off (and catch the rear gasket): there are a few tablespoons of coolant trapped at the lower back corner.

Pour that into your previous drained coolant, and when done pour it back into the reservoir. If you've got the coolant bleed bolt (2010, 2011 model years), leave it open while pouring the coolant back in, till coolant starts coming out. For later model years, leave the topmost coolant hose on EGR disconnected till coolant starts coming out. Also, might help to burp the main radiator hose as you pour the coolant back in.