Quote:
Originally Posted by eivad1
hows does keeping it warmer make it get better gas mileage
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The higher your operating temperature - the higher your theoretical efficiency
I should correct that -- the greater the temperature difference, the higher the theoretical efficiency. For everyone that already understands what I am explaining below, I'm doing my best to keep it as simple as possible
There is something called the Carnot cycle theorem. To help explain here's a diagram :
This is saying, given a temperature difference (hot and cold "reservoir"), a certain amount of heat will flow in - a certain amount of heat will flow out (lost forever) and you'll get a certain amount of work.
The efficiency of the Carnot cycle is:
efficiency = 1 - Tcold / Thot
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So what am I blabbering about? Well, we cant change our cold reservoir (pretty much defined by our air temperature). But, we can increase our operating temperature which in turn increases our hot reservoir (hot gases after ignition will be a little hotter). So, we have increased our theoretical maximum
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The Carnot cycle does not model our Otto engines exactly (but it does make it easy to explain). In reality, Carnot assumes isothermal (temperature does not change) heat addition and heat rejection - but the Otto cycle is not the ideal scenario. The Otto cycle has isometric (constant volume) heat addition and rejection.
Lastly - the trade off. This isn't free. The trade off here is wear. Ideally, you want to run a hot as you can. But, the cost is more wear. How much - I can't say - it may not even be significant over the life of the engine. But you will be adding more heat to your engine and it's surroundings.
A pity too - my T-stat is 190 degrees from the factory... There's not exactly room for improvement :P
SVOboy 
Hybrid Mode
