Heater Mode And Mpg - Why?

[fatboy_daveb]

Hi all

I've been driving more or less every weekend to see my daughter in south Manchester. From my home, this is a 460 mile round trip. Obviously due to the cold I have always set my heater to Auto on 22C with the A/C off, and with the cruise control set at 70 mph (by the speedo) in ECO mode. Results have varied becuase of rain etc, but on average the computer display would read about 53 mpg. I know that it is off by about 4mpg in reality bit it serves as a reference. I was getting about 48.8 mpg on the display when I stopped at Southwaite services heading south. I remembered this YouTube video on Prius Hypermiling techiniques and this guy mention putting your heater on HI (Max temp) with full fan until you car was hot enough and then hitting the OFF button. I had it in front (face) position and not feet/defrost which is what I get when I hit AUTO . Before doing this I reset the MPG display and off I went. By the time I arrived in south Manchester, the mpg display was saying 64.5. I was a bit shocked. That was a 100 mile stint. Being a bit of a sceptic, I did some reading on PriusChat and found that depending on what heater mode you pick, the car will choose one of 3(?) heaters. Not being sure that this was a one off, I decided to repeat the experiment but for the whole 230 mile journey home (M6/M74/M73/M8/M77). Again put the fan on full and selected max temp with the mode in front (face) mode and away I went. The average outside air temperature was 7c and dry, similar to what it was the day before. When I got back the display was reading 61.8mpg. That's nearly 9 mpg than I get as per normal. I filled up (36 litres) and the 'real' mpg worked out just over 57.3 mpg. Can anybody tell me why this is happening? I understand that there are different heaters but this is strange. Is it because the cabin temperature is really hot and the Battery like this (assuming that the rear seat vent sucks in cabin air)? My car has done 7000 miles, almost exclusively motorway miles at 70mph (speedo, but average (true) speed is 65mph). One thing I should mention is that this is an Auris which has a slight higher drag coefficient (0.28) so I never really believed it would ever be quite as good as the Prius at motorways speeds.

That said, two things I did notice: the electric motor seems to be assisting more (via the display) and the cabin is really uncomfortable with the heat. I ended up opening the front windows by a half inch just to eject the hot air.

By the way, after I filled up, I done 3 miles at 70.6 mpg...which I believe is my car's 'official' urban mpg...wouldn't have believed it if I hadn't seen it. Got the flashing 'EXCELLENT' when I switched it off

Cheers

Dave

p.s. the fuel was standard morrisons unleaded...nothing fancy.

[Grumpy Cabbie]

Personally it sounds like a complete coincidence. I can get 60 odd mpg with ease just by taking it steady, even at motorway speeds. You don't even need to turn the a/c off as the system is different to 'normal' cars as the a/c is electrically run. Also, you don't want too much heat in the cabin as the HV Battery isn't a fan (pardon the pun lol) of getting too hot. I would be surprised you didn't hear the HV fan kick in - it sounds like an old hairdryer.

[fatboy_daveb]

Cheers for the reply Grumpie, it's always appreciated. As I said, I never expect to get similar MPG to the Prius purely because the the drag coefficient not being so good. The stuff I saw on PriusChat was concerning the PTC heater arrangement. I was wondering if I was missing this out and getting better MPG because of it. Apparently it works from the electric motors coolant in defrost/feet mode, which is what I always get in AUTO. I had a theory that I was taking excess heat away from the engine and therefore the big radiator fan was not kicking in (the Auris engine bay is quite cramped so I assume there is one). This was a trick that some Mazda Rx-8 owners used to do, my self included, so that we could get 30mpg on motorway runs at 70 mph.....don't laugh...it's true (known as the 300 mile-club from 13.2 gallons!). Basically it was seen as free heat..if that makes sense, and better than using the climate control. This was all to do with the heater matrix, which I assume that, again, I am expoliting.

The chap who I referenced on YouTube is:

Comments would be welcome. I'll be repeating the experiment next weekend.......but when the warmer weather comes in I'll probably stop as the cabin temperature would mean no clothing

Cheers

Dave

[capnbirdseye]

resetting the display halfway thru a journey will give wildly misleading mpg.

I can drive a nearby 12 mile trip midway thru a tank of petrol and the average will hover around 53-56mpg (gen2). If I reset the mpg setting then take that same trip it will show around 64mpg when I get there. Same as if I reset the counter just as I get on a motorway and keep below 60mph it will show 68-74mpg or more for mile after mile but if I didn't reset it then all the lesser journeys during the previous days will be taken into account and it might show up to to 58/60mpg.

Don't know how you normally stand 22c in your cabin let alone higher temps, that's way too hot for us,lol, we set the fan to lowest setting -screen & feet and the heater at 18c which keeps the cabin nicely comfortable without getting stuffy.

[Bike Nut]

Hi fat_boydaveb. I tried this today in my usual driving patterns at work, on each journey I set the temperature as per the video clip and once the cabin was warm enough I pressed the off button on the heater control panel. The cabin did not get too cool, but my longest journey was around 20 minutes so could prove uncomfortable for a longer journey. My usual average MPG for an average day is around 56MPG (indicated) heating on auto, a/c on and temperature at around 20C, I got home tonight having covered 53miles and I have 61MPG (indicated). The temperature outside was 0C this morning and rose to 7C so it was no warmer than over the last few weeks. I am going to experiment with this for this tank of fuel to see what I get. I will post the results.

[ashpole]

Hi Dave,

Thanks for starting this thread, a real gem. I understand P&G but hadn't really got it to work on the Auris. Having read this thread and watched the video I've been playing around.

Observations:

I've now been able to confirm the correlation between the Prius HSI display and the Auris HSD "rev counter" - it's logical and as you would expect but I just couldn't confirm the relationship.

The heater trick seemed to work but this week I've mostly shut off the heater due to the solar energy - I believe it's something called the Sun...!

One of the key points I hadn't picked up on in town and highway P&G was to get the HSD into electric only mode. I had been backing off the throttle after accelerating instead of lifting off completely to make the ICE to electric transition.

I've just been out around town on 30 and 40 MPH roads from a cold start. Normally, outbound I wouldn't get an MPG reading on the switch off display ie it would be less than 45 MPG, today I got 49 MPG. After a short break (10 - 15 mins) I drove back, instead of the usual 52 MPG I got an EXCELLENT 70+ MPG! That's the best for that journey in the six months I've owned the car.

The HV Battery was clearly being worked hard, harder than I've ever seen it - normally it stays one bar down from fully charged and that's it. By forcing the transition to electric at 40MPH made it work for a living! It was up and down like a yo yo! I realise it will also need to be charged more often but there's plenty of hills around here for that to happen naturally (instead of wasting kinetic energy if the battery's full up).

More experimenting to do and I'm enjoying doing it!

Cheers.

[capnbirdseye]

I've just been out around town on 30 and 40 MPH roads from a cold start. Normally, outbound I wouldn't get an MPG reading on the switch off display ie it would be less than 45 MPG, today I got 49 MPG. After a short break (10 - 15 mins) I drove back, instead of the usual 52 MPG I got an EXCELLENT 70+ MPG! That's the best for that journey in the six months I've owned the car.

Cheers.

Did you do this without resetting the average mpg counter at any time during the trip?

[fatboy_daveb]

Hi

Glad it is proving to be enlightening to some people.

To make a point to capnbirdseye, if you re-read my initial post you will see that I said that I stopped at Southwaite services on the M6. At that point I was only getting 48.8 mpg. I stopped for nearly 30 minutes (had a burger and a read of Car Mechanics mag). Before setting off again, I reset the average MPG display back to zero. The engine was not completely cold at this point although the temperature bar was on the bottom. So to the car, this would bee like two separate motorway journeys albeit 30 minutes apart. And as I said, I thought this may have been a fluke so when I done the return trip (non-stop) and got 61.8 mpg, this was front a completely cold engine start. So I am pretty sure that the display was not wildly out, as the amount of fuel used at the pump has shown.

My original question was why did the tip in the video seem to work? After doing a bit more reading, it would appear that the PTC heaters are very low powered and that explains why at 22C on AUTO I found my cabin just too cold even on very long journeys. By moving the heating from AUTO to manual in front (face) setting it seems that I am extracting excess heat off the engine. I have since tried this with my OBD scanner and can see that the coolant does drop slightly. I have also found that setting the temperature at 24C with the fan off at 70mph brings the coolant down a bit and it is much more comfortable to live with, i.e. you don't feel like you are burning your face off. I am beginning to suspect this may be an aerodynamic feature of the AURIS's front grill that is possibly not shared with the PRIUS. What is more worrying is what will happen in the summertime? Even with the heating off, do I expect to constantly hear the radiator fan as well as possibly the battery's fan as well? And how will this affect my economy? In three months time we'll find out I suspect.

Ashpole, glad you found the video's driving tips useful. One thing it probably doesn't tell you is not to use the cruise control on hills. Although I regularly use it on the motorway, I have found that I get better mpg when using my foot on the accelerator instead. It's just a real pain doing that on a 230 mile drive...ok, I'm being lazy but the car's equipped with it so I going to use it.

And as I said before, us poor AURIS owners are never going to get the same mpg as a PRIUS at motorway speeds simply because the shape of our car produces more drag. That's a shame, but that's the price you pay for having the ability to have nice clear view out your back window

Cheers

Dave

[ashpole]

Did you do this without resetting the average mpg counter at any time during the trip?

Yes. The Auris HSD has an end of trip display which is reset at start up and comes on when you turn off the ignition - if you get more than 70 MPG you get an added flashing "EXCELLENT"....

[ashpole]

One thing it probably doesn't tell you is not to use the cruise control on hills. Although I regularly use it on the motorway, I have found that I get better mpg when using my foot on the accelerator instead. It's just a real pain doing that on a 230 mile drive...ok, I'm being lazy but the car's equipped with it so I going to use it.

Yep, the cruise control is a double edged sword, but I wouldn't be without it for when I want to use. When I do use the cruise control I also engage ECO mode, that way it seems to dampen its response just like when you're using your right foot!

[ashpole]

I'll be repeating the experiment next weekend......

How was it?

[fatboy_daveb]

Hi Ashpole

Sorry for the late reply. Last weekend we had snow in Glasgow so the experiment may have been effected by the lower temperatures. I still had the heater set on front (face) but never actually turned it on. After about 3 minutes I started feeling a small amount of heat coming through as I headed for the motorway. I drove at the same speed with cruise control on (in ECO) and got got 57.8 mpg according to the pump. The next day, on the way back, the ambient temperature was up by about 8C, I set the fan at 24C (more comfortable) on full blast when I started. That lasted for about 3 minutes as it was pretty hot. I turned the fan off and returned to Glasgow at the same speed as i did before and I got 60.4 mpg (fill to fill). I am beginning to think that most of this 'improvement' is to do with me not running the car's heater in feet/defrost mode on AUTO, but with the car in front (face) mode where it seems to take the heat off the engine. According to the manual the Auris HSD has two huge radiator fans, so maybe my antics are causing them not to be used as much.

Either way, I am definitely getting an improvement from not running with the heater on AUTO for the length of the journey. Yetserday, I was taking my ex- and my daughter out for a meal when the ambient temperature was 13c and got 72 mpg on the display. On seeing it, the ex- said it must be broken and that I should turn the heater off. It wasn't even turned on . It was just the heat floating through from the engine.

Cheers

Dave

[ashpole]

Hi Dave,

You're not late, I'm eager! No problem.

I'm seeing similar results but been able to drive around without the heater on and the temperature set to 19/20 to get some cooler air into the cabin. The results I'm seeing are stunning: I've had more EXCELLENTs in the last couple of weeks than the previous six months. Yes, it's getting warmer but using the power and glide technique ie forcing off the ICE, makes a worthwhile difference too.

In terms of numbers, the single trip average consumption readout has topped out at 72 MPG on a couple of 20 mile trips but mostly been around low to mid-60 MPG, just below the EXCELLENT threshold of 65 MPG.

I'll be reporting my full fill-up to Fuelly at the end of March, I'm adding £30 splashes until then as I'm getting an equivalent 20p/L discount from Amex/Tesco.

Cheers,

Mike