Winter Mpg Fall Off

[jonb12340]

This is my first post but I have been reading posts here since April. I have learned a huge amount through this forum and thank you everyone for your wisdom.

I own a 2009 Gen 3 Prius which I have had since April, I am watchful over my MPG and have noticed, as I think previously noted it falls away as the weather worsens. My question is how much?

I was getting around 60mpg in the height of summer. It fell back to about 58mpg as the starting temperature got to around 13c. I am now at about 55mpg at about a starting temp of 9c.

Does this sound about right? I ask this because I have just had my (free as part of the purchase deal) 60k service and it was then that I could not get above 55/56 mpg. 'Could I have been filled with the wrong oil' is my suspicion. Before I tackle Mr T some opinions would be helpful. Thank you.

[Grumpy Cabbie]

If you get 60 mpg in summer you'll get between 50 & 55 mpg in winter. Perhaps less in a really cold snap.

At the moment your engine will switch off after about half a mile when it's warmed up. In winter with the heater on it'll take longer, maybe a mile, maybe two or three when it's -5c. Then the engine will be switching on and off more often to keep the heater topped off with heat.

You could use Eco mode as that causes the engine to switch off earlier, but then you'll be colder for longer. Or maybe let the car warm up in normal mode and then switch to Eco when you're warm enough.

Don't worry about it and don't bother with grill blocking etc. It's just not cold enough in the UK for that.

Regarding the 'wrong oil', yess it does affect economy. Check your tyres first as many dealers will lower the psi for some reason only known to them. The 5w30 oil is thicker (and cheaper) and will cause a quieter engine but it does affect mpg's. I also found the car would 'stumble' when the engine fired up in traffic compared to the thinner 0w20.

[PeteB]

yes, everything GC said, and check they haven't overfilled the oil - that often seems to happen and can harm the mpg too.

[Chris Dance]

Did a return journey of approx 100 miles today; no motorways involved. At the end of both 50 mile runs achieved 65.9 MPG. as shown on the car at shut down. I kept the car in ECO mode. OAT 13 degrees this morning and about 17 degrees this afternoon. I was well pleased with that result. Car has done almost 300 miles.

[Grumpy Cabbie]

It'll get better as the car beds in. Consensus is that you start to get the proper economy from about 5,000 miles onwards.

Just make sure they fill it with 0w20 oil at service at 10,000 miles though :)

[johalareewi]

You can get a good idea of the winter/summer variation by checking the fuelly history of gen3 owners. ;)

For example

https://www.fuelly.com/car/toyota/prius/2010/johalareewi/30847/fuelchart

Grill blocking on a gen3 is easy to do if you want to have a go.

For me it does improve the mpg during winter but YMMV.

You can do it with a couple of lengths of foam pipe insulation.

It will simply push over the horizontal grill bars.

Cut it to length, and cut out 2 or 3 notches where the grill bar has a vertical cross member.

There is enough friction to hold the foam in place, or you can use some string to make sure.

If the weather warms up, the foam can be peeled off and put in the boot until it gets cold again when you can push it back on.

Warning:

On the gen3 prius, block the lower grill.

The upper grill cools the inverter so best to leave it unblocked.

[PeteB]

of course, the level of winter drop will vary from owner to owner, depending on things like how many journeys are very short, and how heavy the right foot is during the warm-up phase.

When I had a Gen 1 Prius (much less clever than the current models) I had a daily 40 mile each way commute across gentle cross country roads with light to moderate traffic, and hardly noticed any drop at all in the winter.

Most of the time, my right foot is quite gentle, too!

[jonb12340]

Thanks for comments so far.

Toyota did under inflate the tyres, they are now restored to 2psi over Toyotas recommended.

I suspect my winter fall off so far is down to a heavy right foot. I am using Eco now and have pushed mileage to an average of 56.5mgp in a relatively short journey ( 20 miles my average) but it still feels a little low. Foot training needed!

Sent from my iPhone using Toyota OC

[PeteB]

Another key is reading the road ahead and anticipating things like traffic lights - lifting off earlier increases regenerative braking and if you think lights are about to change in your favour braking early and keeping the speed above, say, 15 mph, will give better economy than braking to a stop and setting off again 3 seconds later.

Of course this is all true for any car, but Hybrids are helped even more.

Braking gently so the ECO gauge just reaches the left end of the CHG area will maximise regen, whereas braking harder still just wears out you discs/pads a bit as well and wasted the extra energy that would otherwise be saved for later.