MPG worse after replacing battery, PCV valve, spark plugs, cleaning fuel transmission?

None of the things you did as service to the car would reduce the mpg. So therefore I believe it's due to the AC use. The real measure is after 2 tanks of gas, you should be able to get your average you had before.

What the heck is cleaning fuel transmission system? Fancy way of saying throttle body cleaning or fuel injector cleaning?

 

welcome to priuschat! how long have you owned the car? sounds like you got it fairly recently and don't really have a good track record of mpg's yet. are you in hill country, or hot climate?

 

You say 'the battery' was replaced. Which battery was that, the 12V battery or the high voltage (or traction or hybrid) battery?
Was the Check Engine Light on? What codes did the shop report?
What is the tire pressure?

Please answer as much of this questionnaire as practical. If you are not actually new to driving a Prius, then the stuff about your previous car is no longer useful.
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

 

Also, if you had the tire presure upped, the dealership would have lowered it to door sticker standards which usually runs around 35psi

 

This depends on the dealer. The shops where I bought my Prii have never lowered it. Not even for PDI from the factory overpresssure for the Pacific boat trip.

But a service stop during an extended road trip lead to a verbal argument with the mechanical about my 'dangerously overinflated' tires. We finally compromised at 40 psi, the highest he would allow out of his ship. It turned out that that wasn't enough allowance for the difference between the highway-warmed and morning cold, plus the next day's 6000 foot descent, leaving my rear tires barely OK, but fronts underinflated.

 

Usually a temporarily lower MPG value is a consequence of removing 12V from the system. Either disconnecting or replacing battery. More reasonable values should soon return. Unless, of course, they don't ...

 

EXACTLY the same issue i'm having. Really weird how similar the situation is for me. I just bought a used 2005 Prius with 153,000 miles on it, and it seemed to be getting similar mpg to my original 2008 Pri before I had it serviced about a week later. Then, after getting the Inverter coolant, engine coolant and transaxle fluid changed at the dealership my mileage seemed to drop significantly from about 44mpg city to about 36mpg. Actually, it was all over the place for the next few days before it 'stabilized' to around 36. I took it back to them and they said it wasn't uncommon for mpg to be irratic after service because they sometimes have to put the engine in a long full-run mode while just in the shop for an extended time, or sometimes need to disconnect the accessory battery which can reset driving history. I was concerned about the traction battery, but they said the computer hadn't thrown any codes and not to worry about it.

That said, over the next two weeks I changed the plugs, cleaned the injectors, cleaned the throttle body, inflated tires to 42/40, ran the AC on low, and put in my brand new accessory battery from my old 2008 pri. It has creeped back up to about 44mpg after a full tank average, but still nowhere near the 50+mpg I was seeing when I first bought the car.

I do a lot of short (under 10mile) stop and go driving in town mostly. What I'm seeing consistently in the MFD is 25-30mpg the first 5 minutes of driving, then about 35-40mpg for the next 5, then 50+ steady after that. This process repeats very consistently if the car is left unused for more than 4 hours.

To me, it simply feels like the traction battery will no longer keep a charge when not in use. It's like the engine spends all of its time charging back up the battery the first five minutes (I see this activity in the MFD).

Anyone have any thoughts or similar experience of this behavoir?

Thanks,
Mike

 

I doubt it, it spends the first ten minutes warming up the ICE.

From what you've described, it sounds like perfectly normal warming up behaviour to me.

To achieve the best FE, you should drive gently in the first 10 mins or so of driving.

Bear in mind if they have left the car in inspection mode (as they would for your coolant change), that will take a hit on the current tank's average. If they disconnected the 12V battery, then it could take up to a month for the engine ECU to relearn the best settings for your driving style. Also, I think this affects only what is displayed on the MFD's average and not the real life consumption. (Do you use Fuelly to record your MPG?)

I'd say not to sweat it unless it's been longer than a month since the service or since the 12V battery was last disconnected.

hope this helps

 

^ The dealership might have left it idling, bad for mileage, yes. But I can't buy into the car "getting to know you"

 

It is a documented process, do a search. The engine ECU sets certain aspects of the engine management according to how you drive to optimise economy.

 

And when your partner hops in the car, it does what?

 

Unless you have trained her to drive properly it starts to learn her style. It can make it hard to achieve consistent consumption figures.

And if you think I'm making it up, I recently had to assume all driving duties as my wife was medically unfit to drive. In that time I was able to get consistently improved FE figures improving from 4.9 - 4.8 l/100 km (48.0 - 49.0 mpg US) to 4.4 l/100 km (53.5 mpg US).

Now that she is driving again, tank averages are back to 4.7-ish.

 

Hi Mendel, it's true, the ECU's have to relearn if the 12v is interrupted. I thought the transmission was going out on my Rodeo after I put in a new battery! It was jerky and shift points were all over the map for a while. Your MPG will come back when it's ready. If anything was wrong, you'd see DTC.

 

Thanks! And yes, I am a VERY slow driver and do all the right things to increase mpg. Typically I accelerate at just one mph per second. It takes me 45-60 seconds to get her up to her sweet spot which is around 55. lol

 

Actually, no need to take it so slow. A brisk acceleration is more efficient in the long run. From a standing start, initially accelerate at 13 mpg (16 UK mpg / 18 l/100 km) until about 15-20 mph and then feather to 20-26 mpg (24-31 UK mpg / 12-9 l/100 km) until you've reached your target speed. The quicker acceleration will balanced by cruising at optimal gas usage for longer-- depending on conditions, I normally fluctuate between 50-94 mpg (60-113 UK mpg / 4.7 -2.5 l/100 km) while cruising at 57-60 mph. Give it a try.

 

Another one hit wonder? There's a pattern developing here. Suggest no more time is wasted unless we hear back.

 

...Emma might just be a very good listener.

 

Yes OP never came back, but new poster Mike is now receiving help in this thread.

Yes Mike, I think this is starting to become somewhat more common with older Prius as the traction battery ages.

First let me say that the service was probably just a diversion. As long as the oil wasn't overfilled, or the tires under inflated, or the accessory battery run down, then I don't think it's anything they did. The reported (and probably also the actual) fuel economy does indeed dip for some time after the accessory battery has been disconnected.

Given the apparent relation between the low mpg and the low SOC (state of charge), you may also have the issue that I initially referred to with older Priuses. When the Prius first starts there is a very high demand on the traction battery for the first few minutes, and this can cause a drop in SOC that is most noticeable on Prius with more aged batteries.

The high demand is basically due to three things.
1. The computer tries to use electric propulsion, in preference to engine, until the engine warms to a preset point. (This is the major one).
2. The aircon compressor initially runs flat out (at any setting) if the car starts out very hot.
3. The DC-DC converter (powered by the HV battery) often supplies quite a lot of current to get charge back into the 12V battery. So this is another load that starts out fairly high but tapers back after a few minutes.

The work around is very simple, just leave the transmission in "P" and let the engine warm for about 50 seconds before driving (hold the brake and just tap the accelerator once if you need to force the engine start). Most people believe that this will waste fuel and hurt fuel economy, but surprisingly it can actually improve it in cases like this (that is, where dropping SOC in the first few minutes is a particular problem).

So give it a try. It will also help greatly if you can use the windows to flush out the hot air and delay the aircon usage for one or two minutes after starting.