Optimum ambient temp for ICE?

I find my Prius gives me the best gas milage in the 50+ to 75+ range. Under 40 it seems to run a different warm-up program and above 85 it has to use quite a bit of compressed air.

Hope that helps

 

Compressed air? For the AC, or what? I've still got most of my insulation blocking the front grill and it's hit 90F out here in Atlanta already. I haven't seen any problems with heat, but to be fair I almost never drive it more than 30 minutes at a time, so that could be it.

Could be that I've got the older model, but the higher the temps the better it's been for me. Even now when it's over 80F almost every day, sometimes when I'm coasting for a while it'll still have to turn the ICE on to keep stuff warm. Not sure why, since I don't coast THAT long, not even a mile.

 

70 DEGREE C and 90 degree C is the sweet spot for engine efficency, when your engine climbs above 92 degrees C the engine coolant or water pump kicks in to provide adequete cooling to knock the temperature back down to 86 degrees C and the cycle continues. Everytime you need to cool down the engine that's a conversion lost (aka mpg loss) (from engine to water pump vice versa) so try not to overheat your engine

i'm sure there's a number of times the water pump can operate before being extinguished... but i'm sure that number has to equal 100,000 miles before changing the engine coolant again.

I usually try to keep it at 1500 rpm when coolant reaches 70 degrees C ( stage 4) to prevent any additional heat from reaching the engine, although in the end heat is going to get there no matter what, at least when your soft with the rpm the heat is just isn't as intense and during your trips in EV mode the engine will get a chance to cooldown without the aid of the water pump, saving efficency losses!

 

Daniel, I believe the car runs better (higher mpg) with OAT (Outside Air Temp) in the high 60's. In the evening with temps in the 80's-90's it takes a lot longer to get the mpg back up.

<div class='quotetop'>QUOTE(JimN @ Jun 8 2007, 08:31 PM) [snapback]458410[/snapback]</div>

BTW, the insulation for the upper grill went back in place.

 

Japanese hypermilers are saying 35C (95F) intake air temp is the best.

Ken@Japan

 

<div class='quotetop'>QUOTE(ken1784 @ Jun 8 2007, 08:00 PM) [snapback]458432[/snapback]</div>

It gets to 95F in Japan? How serious are the Japanese Hypermilers, do they drive when 95F with windows rolled up and AC off to get the best mpg? :blink:

 

<div class='quotetop'>QUOTE(abq sfr @ Jun 9 2007, 01:02 PM) [snapback]458504[/snapback]</div>

Sure!
But, please note that it is an intake air temp.
We block upper grill and two thirds of lowe grill even in summer to keep the engine room warm.

The real Japanese hypermilers never use AC and never drive on highway.
http://www.cleanmpg.com/forums/articles/t-...-2006-1793.html

Ken@Japan

 

<div class='quotetop'>QUOTE(ken1784 @ Jun 9 2007, 08:54 AM) [snapback]458602[/snapback]</div>

I have a question related to this: What is the warmest that you should let the engine's coolant temp get to when blocking off the grill? I'm picking up some pipe insulation material today and am planning on doing the grill block. Thanks.

 

Max 'happy' engine coolant temp? Well, you don't really want to pressurize the system, so below 100 oC (212 oF). From all reports, it is quite difficult to get up there.

The engine fan will run above about 95 oC (204 oF). This is an additional few hundred watts of load, so maybe you don't want that. It could be considered avoidable wear on those components, as well. As I understand it, both fans always run when the A/C is lit, so that represents part of the energy cost of that mode.

The coolant thermostat starts to open about 85 oC (185 oF), but there is no particular energy cost associated with that.

I imagine that efficiency improves (slightly) all the way up until the fans start to spin, and so, suggesting right around 200 oF. A grill block may not be enough to achieve that, several months of the year. Do you have some sort of scanner to keep track?

There is no advantage to warm the inverter coolant; in fact there it's 'the cooler the better'. An NHW20 expert may advise how to keep that system cool during all this blocking-off.

 

<div class='quotetop'>QUOTE(diamondlarry @ Jun 9 2007, 10:25 PM) [snapback]458611[/snapback]</div>

I think it is a good question.

In Japan, the highest temp is about 95F and we never heard that Prius got over-heated, has anybody?
Prius engine only runs 50% or less, sometimes less than 20% of distance.
The engine becomes too cool especially in winter.

So, you can block the upper grill in all year around.
As I wrote, we block the two thirds of the lower grill even in summer.
But, if you drive on long uphill, I think you had better not to block the lower grill for preventing overheat.

Ken@Japan

 

<div class='quotetop'>QUOTE(tochatihu @ Jun 9 2007, 10:13 AM) [snapback]458625[/snapback]</div>

I have a Scanguage2 that I have one of the guages set to coolant temperature. I blocked off all but the bottom 2 grill openings. ken1784, thanks for the information. It doesn't get much warmer than 90-95*F very often here either so I will just keep an eye on the coolant temp.

 

<div class='quotetop'>QUOTE(Daniel Sefton @ Jun 8 2007, 06:03 AM) [snapback]457954[/snapback]</div>

There are really 2 answers:

One is the air intake temperature for the combustion process. A temperature of 60 to 70 Deg F is optimal here. As the air intake gets hotter, the process becomes more inefficient.

The second is keeping the engine warm. That operation requires coolant temperatures of 180 to 190 deg F. An engine could be kept even warmer (say as much as 400 Deg F)... but metallurgical limitations dictate a cooler temperature.

Keeping gear box and inverter temperatures at 60 to 90 deg F... will help operate those parts best when you consider the fluid viscosities.