First Cold Morning

I have both upper and lower grills blocked. When the outside temp was 8C yesterday my car reached 87C coolant temp after about 6 blocks - perhaps 3 - 5 minutes (lights etc). I saw 90C once. Temp drops slowly at lights, perhaps 1C per min. I'm still debating with myself (warning, I talk to myself often) whether to leave A/C Auto on. Currently it's off, cabin temp set to 21C, fan speed to one above min. I now seem to be stuck at 4.9 l/100 km. Will be filling up this morning and resetting the mileage so I'll see if there is any small change in the next few days. I don't use my block heater, as I can't really predict when I'll be driving the car the day before (retired).
Some of this may be due to the new tires (Nokian WR). Not broken in yet.

BTW, this is the same mileage I got for the first month the car was new. So it's not too bad, as it's about 10C colder than then.

 

Whoa! OK, I know the MFD readout is not "accurate", but mine has always been pretty close (the fuel mileage or l/100 km part). So my comments above were based on it. So I just filled up, and when recording my data in my fuel use book, I also discovered an error in the previous tank calculation. Last two tanks average about 4.2-4.4 l/100 km!!! MFD said 4.9! It's like finding an "Easter egg". I wonder if the error in the MFD is due to the cooler weather?

Whatever, I'm very happy again. My tires, the cooler weather, and whatever else I was blaming for my dropped mileage are off the hook!

Do note that the MFD outside temp measurement will be thrown off when you block the grill openings. The sensor is just in front of the A/C radiator. My rad. blocking has two 3" semicircular "holes", one on each end of the lower grill. So the car can get -some- outside air through those. Forward motion does not force much air through them as they face each side, but the fans can draw some air through them. I haven't heard the fans run however.

 

<div class='quotetop'>QUOTE(Tideland Prius @ Oct 18 2007, 09:16 PM) [snapback]527573[/snapback]</div>

I'm a new Prius owner. After my first fueling I get MFD=5.2 vs Calc=4.31. :huh:

It must be because of the "bladder" in the fuel tank and also the fact here in Quebec weather at this time of the year vary greatly. 15C one day, 5C the next morning.

 

<div class='quotetop'>QUOTE(Tideland Prius @ Oct 18 2007, 10:33 PM) [snapback]527612[/snapback]</div>

Ok so according to the training document from that topic what is the bladder all about?. The Energy Monitor should be the most accurate to use ? Correct ? (see below)

 

<div class='quotetop'>QUOTE(gazz @ Oct 19 2007, 02:22 AM) [snapback]527654[/snapback]</div>

I wouldn't personally worry about 95C coolant temp. It will not boil until around 120C. It's actually better for the engine if it's up in the 90s C.

As I said, mine has the two semicircular openings, one on each side. They are the "ends" of the circular pipe insulation which I left open, first, to access the block heater cord (it resides just inside the insulation), and second, in case the fans do come on, there will be air they can move. So they probably won't stall. I don't like it when electric fans stall, as they speed up too much.

When you hit 95C, did the fans come on? Mine don't at that temp. unless the A/C is on.

A picture is worth a thousand words.
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My MFD readout has always been just a little pessimistic, but close. I use it for quick and easy estimation of fuel economy, or to see what I can do to improve it. When I want to KNOW what my fuel economy was, I use calculation over several tanks. The more tanks, the more accurate. Of course, if you use a lot of tanks you are averaging the numbers over quite a few weeks (I'm currently filling the half full tank about once a month). ie - Yesterdays fillup was 24 litres. Last fillup before that was the middle of September. It was 21 litres.

 

A few things to keep in mind.

First, the temp sensor is not going to be really accurate. It's a production sensor so probably +or- 10% at best. I have seen 87C as a "normal" coolant temp in summer, and it will drift up to about 90C when the engine is working hard.

Then there is the little problem that many don't realize - the temp in the system varies depending on where you measure it. I would expect the thermostat to open when the coolant flowing through the bypass circuit reaches 80C, but I'm waiting for someone with a manual to confirm. The bypass circuit runs to the heater and is used to ensure the thermostat has coolant flowing over it at all times so it can actually sense the coolant temp - when the heater is shut off the flow still continues, just around the heater core (yet another bypass - in the bypass circuit). But the sensor location is not the thermostat location. So there will be a difference between the sensor readout and the temp at the thermostat.

As far as when the fans come on, it depends on whether you have the A/C turned on or not. There are two fans, and they may come on in a staged fashion as well (many cars do this). Mine have not come on even when the coolant readout on the Scangauge was 95C - I didn't have the A/C on. I haven't seen 100C yet, so I can't comment on temps above 95.

As I said, I don't think there will be a problem with the engine coolant, at least not with ambient temps of 20C and lower (that's around 70F for those metrically challenged ). I can't comment on the inverter coolant loop temps as I can't see them. So I worry about -them-.