Keeping yourself warm/saving engine heat and MPG

[California98Civic]

Originally Posted by Frank Lee

I've always figured that it didn't really matter where the temp knob was set as far as mpg and warm-up time; I thought if the blower was off it wouldn't exchange enough heat to really matter. But then, I didn't have the instrumentation to really check it out either.

The difference in warm-up time between heater control cold or heater hot can't be much, can it? And after the engine is warm I don't see how heater control knob position can affect mpg at all. However I can see a negative mpg effect from the alternator load increasing with higher blower settings.

Watching the coolant temp and just shifting the temp control I can bring the temp down from say 204 to 194 or 190 in a few seconds. No fan at all. Watching my voltage meter and switching the heater fan on I can watch the voltage start to drop by increments of a tenth of a volt per fan speed level. But you're right: I have no sure idea how much or if my position of the temp selector to cold improves MPG or warm-up time because there are more variables. However, I have observed that it SEEMS that as the car warms up during driving, I may be able to make the coolant temp fall from say 120* slightly faster during an EOC glide if the heater temp selector is in the red. But again, not sure of that last observation. I'm just assuming that if I can manipulate coolant temps that easily, then there's probably some effect on FE. Hypothesis.

[Cobb]

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[RobertISaar]

Originally Posted by Frank Lee

The difference in warm-up time between heater control cold or heater hot can't be much, can it? And after the engine is warm I don't see how heater control knob position can affect mpg at all. However I can see a negative mpg effect from the alternator load increasing with higher blower settings.

certain cars have a ventilation system that forces air through it due to high pressure zones on the blower intake area, so the faster you go, the more air gets forced through it with the blower not contributing to the airflow. if you have the position selector set to move air through dash vents, go 50MPH or so with the blower motor off and see if you can feel air movement. if so, it won't be much, but it will be something.

others have a completely "sealed" system that has absolutely no airflow with the blower off.

others yet have systems where the blower motor is on at all times, although at a very low speed to where you usually won't be able to hear it.



it's all dependant on how your HVAC system was designed.

[nbleak21]

Originally Posted by Frank Lee

The difference in warm-up time between heater control cold or heater hot can't be much, can it? And after the engine is warm I don't see how heater control knob position can affect mpg at all. However I can see a negative mpg effect from the alternator load increasing with higher blower settings.

Actually you'd be surprised at the difference it can make, both from amp draw and from additional cooling via heater core. I've experienced both during below freezing commutes, fortunately the weather has been a bit more mild the past couple weeks and I have been able to get by with a jacket and no car heat.

[ECONORAM]

Originally Posted by RobertISaar

certain cars have a ventilation system that forces air through it due to high pressure zones on the blower intake area, so the faster you go, the more air gets forced through it with the blower not contributing to the airflow. if you have the position selector set to move air through dash vents, go 50MPH or so with the blower motor off and see if you can feel air movement. if so, it won't be much, but it will be something.

others have a completely "sealed" system that has absolutely no airflow with the blower off.

others yet have systems where the blower motor is on at all times, although at a very low speed to where you usually won't be able to hear it.

it's all dependant on how your HVAC system was designed.

I agree, the HVAC design plays a role. My truck's heater core gets hot coolant all the time?! Yes, even in summer. I installed a bypass valve so I can shut it off in summer if I want to. Haven't thought to test it and see if anything changes...might check yours.

[slowmover]

Originally Posted by ECONORAM

I agree, the HVAC design plays a role. My truck's heater core gets hot coolant all the time?! Yes, even in summer. I installed a bypass valve so I can shut it off in summer if I want to. Haven't thought to test it and see if anything changes...might check yours.

This dehumidifies the air in the plenum being used for cooling. I also use a valve, but only in the hottest part of summer . . the dehumidification operation works well (at least on my CTD). It is not as sophisticated as it should be . . Chrysler has had less than optimal HVAC in trucks for many years (though newer than mine may be better).

Some systems -- if not mentioned -- also have a loop that allows for hot cab air before the coolant has actually warmed all the way.

Is anyone using the equivalent of a circulating coolant heater (KIMM HOTSTART) to pre-warm the engine, and then grille block to keep temps high?

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