Two questions there, I think, with three answers.
1. "Climate control" is airconditioning. Apparently on a car, the air is chilled, and then run through the heater matrix to warm it to the right temperature. So the answer must be "yes" as you are chilling the air first.
2. A car starts up when it is cold, and has an optimum operating temperature.
2a. If the car is under its optimum operating temperature, then having the heater on (assuming the car sends hot water through the heater matrix before it is up to temperature, and I have no idea whether that is universally true) must increase consumption.
2b. If the car is at or above operating temperature, then it has to get rid of its waste heat somehow. Better that it is put into the cabin than that that the engine fan has to be turned on (which will use a small amount of electricity (= petrol)).
Equally, of course, the heater fan will use a modicum of electricity (= petrol).
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Of course, hot air rises and this upward force will reduce friction and so increase MPG.
Sorry! couldn't resist ;-) - have been surrounded by plenty of hot air today.
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>Assuming the car sends hot water through the heater matrix before it is up to temperature.<
Which will depend whether the heater circuit is affected by the thermostat in the same way as the radiator? The thermostat on my diesel takes 5-6 miles to open (it can be seen happening on the temp gauge) but there is warmth from the heater long before that.
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>Assuming the car sends hot water through the heater matrix before it is up to temperature.<
It doesn't. The engine thermostat stays closed until the coolant in the cylinder head reaches running temperature. Then it opens and everything cools down again, especially if the heater cock is open.
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>>It doesn't.
Of course, it depends upon the detail of the cooling system of the car in question, but, it's much more usual for heater flow not to be controlled by the thermostat. This is the case for a number of reasons, among which, the early availability of some heat before the thermostat opens, and the easy, air-lock free filling of the system.
For the main OP's question, yes, undoubtedly.
The cooling of the water in the heater must change the temperature of the engine's coolant. The engine's efficiency must vary with temperature. Therefore, even before the elctrical power which drives the fan is considered, the heater affects the engine's efficiency, and hence, fuel consumption.
Note, I'm not putting any numbers to these points, and, the overall effect may be so small to make it difficult to measure, but, that doesn't mean to say that there's no effect.
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The cooling of the water in the heater must change the temperature of the engine's coolant.
I agre with this, but only up to a point, if the thermostat (are these still fitted on modern cars, hmm?) is OK. So, if the thing's warming up, yes, there may be a difference. When it is warmed up, I don't think so (unless it's, again, a negligable effect).
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>>I agre with this, but only up to a point
I think the thermostat is a confusing issue here - it's actually a red herring.
The rate of supply of heat energy to the engine is finite, and so, if you take heat energy out of the system, via use of the heater, the temperature of the system as a whole must drop.
Mechanisms like the thermostat might act to regulate the system, and reduce the temperature drop, but, if the thermostat valve closes, or moves towards closure, then, it must be moving in response to a temperature drop, which actually supports the point that the temperature of the system drops!!
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much more usual for heater flow not to be controlled by the thermostat.
Not specifically, no. there may be a little bleeding of warm water to the heater. But the normal arrangement with run-of-the-mill cars is for the engine thermostat to stay closed until the cylinder head reaches normal running temperature. When it opens, cold coolant flows into the cylinder head slowly sometimes even causing the thermostat to close again. In any case the flow continues to be somewhat restricted until the system is near running temperature. Once warm coolant is flowing, the heater will give heat.
AS I said, engines normally run a bit too cool. Anything tending to make them run cool, including the heater being turned on, will increase fuel consumption. As I also said, the difference is likely to be too small to be easily measurable.
I dunno about this site sometimes. You say something, then tom dick and harry say bits of it as if you hadn't said a word. Can't people read?
Edited by Lud on 10/09/2008 at 00:30
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Lud, you're confusing the action of the thermostat which does close the flow to the main radiator until the engine warms up with the flow to the heater matrix, which, usually, isn't controlled in that manner.
I dunno about this site sometimes. You kindly offer a correction to a misunderstanding, ....
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Oh heavens, I suppose there are bypasses and things in modern cars sometimes. But the basic system is that the entire body of coolant doesn't flow until the engine starts to warm up, and very slowly after that until it reaches proper temperature. And quite rightly too. Ridiculous to waste energy keeping citizens comfortable when they could be getting an efficient move on.
I dunno about this site sometimes. You call people tom dick and harry and they get all miffed.
:o}
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>>But the basic system is that the entire body of coolant doesn't flow until the engine starts to warm up,
No, that's not true either!
Even cars as basic as an A series equipped Morris Minor allowed water from the rear of the cylider head to the heater, and then back to the bottom hose, by-passing the thermostat completely.
All the engine mounted thermostat does on a basic system is effectively connect and disconnect the main vehicle radiator from the system. Of course, there are weird and wonderful variations on this theme - mainly French!
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On the assumption that nearly all car engines (for failsafe reasons) tend to run too cool for ultimate efficiency
Is that the case? (serious question) given that my car runs at 90c normal - what is the "optimum" temperature?
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It'd make a big difference on a cold diesel car with multiple 150w immersion heaters to boost the heater output - much the same as air-con I'd guess.
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I believe it is AE. I don't think it's as haphazard as it used to be in the days of fanbelts, but my impression is that cars are set to run a few degrees cooler than optimum to prevent them from overheating in those summer traffic jams.
All I can say is that my own car seems to run a tad better when the gauge needle rises towards the red and the cooling fan cuts in and out in slow traffic than when it's wafting down the road at cruising speed with the temperature gauge needle down at the bottom of the normal sector.
As for what the optimum temperature is, I would imagine it varies from one engine to another, within a few degrees. It may be better at 100 degrees or more. Perhaps that's why cooling systems are pressurised these days, to stop the coolant from boiling away.
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what is the "optimum" (running) temperature (for a car engine)?
As hot as possible without causing damage.
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