Adk46

Start up the car, back out of the garage, fuss with the PCM for a minute or two, drive out to the road, and feel hot air coming from the vents! The elapsed time display said "0:02" - less than three minutes.

I've seen the other comments about how quickly the Macan engine warms up, the thermal management devices, but for the 4-cyl at least, wow.

Let's see, cruising along, the engine burns 3 gallons/hour, 0.05 gallons/minute, 0.8 oz/minute, about 2 oz for the time period here. That's at 75 mph. Even with a rich idle mixture, less than an ounce, probably much less. Is that enough to heat up a few hundred pounds of aluminum (and a gallon or so of coolant) to the point where the heater blows warm air?

I'm not so curious that I'll look up the heat capacity of Al, etc. But it makes me wonder if something else is going on, like partially engaging reverse gear along with a forward gear.

worf928

No, the interesting question is: Dude?! Why do you need heat in July?

Is the cluster-displayed water temperature consistent with your buttomometer?

Adk46

HVAC set to 73. Basement garage about 60; outside temperature about 60 - heat comes on!

Modern Porsche coolant temperature displays are programmed to lie so is there any point to look at it? I have not noticed it saying anything other than 200. I like the oil temperature readout.

The first time I noticed the heat coming on quickly, I thought "Gosh, did they incorporate an electric heater in this thing? Or does the AC have a heat pump mode?"

worf928

They only lie in the dead band centered on 'normal operating regime.' At temps lower than the dead band I they don't seem to lie. I know that on our 9[[98]1|5B]s that the water temp display starts at ambient (when cold) and climbs steadily to the dead band.

Also, and I'm not going to bet a body part on this, I *think* it doesn't lie when in Sport Mode. OTOH, it is also possible that in Sport Mode, the embedded software just moves the dead band ~30°F South.

I do seem to recall that the 991's water temp display did vary based upon use when in sport mode.

In any case, if the Macan's circulatory system is like the 928's, the default cold condition is circulation through the block and heater core. I recall - dimly from a long time ago when I used to drive my GT in the cold - that by the time I traveled two blocks it would start blowing warm-ish air.

Aluminum is a good conductor of heat but has a low specific heat capacity. Yes? You're the Metal Guy..

Adk46

OK, there are 128 oz in a gallon, not the 16 I used in my head.

With heat capacities for 200 lbs of aluminum and one gallon of water, and with the heat content of 3.2 oz of gasoline (20% of cruising rate [25mpg @ 75 mph] for 2.5 minutes), and a bunch of unit conversions I might have screwed up, I get a 31°C temperature rise, to about 50°C, 122°F.

So, credible, not incredible. Dave will peer review, but I expect 97% of climate scientists will agree.

The 200 lbs is less than the engine/gearbox under the hood, but perhaps close to that which must get warm to make the heater work. The gallon of water is what I'm figuring circulates inside the engine and heater; antifreeze probably reduces the heat capacity, but never mind. I'm not counting the heat that escapes into the exhaust manifold, or the mechanical energy the engine delivers; this might total 30-40%, now that I think of it.

Other plausible numbers I can use give a range of temperature rise from 12 to 50°C. Keep in mind that I became a metallurgist because I was bad at math.

I must have something better to do, like figuring out why my 928's kick down switch doesn't work.

worf928

Sounds like work. Today's my day off

I'll poke at it after today.