195* Tstat - Page 2 - Fuelly Forums
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Old 04-15-2007, 08:17 AM   #11
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Another thing to look out for is engine pinging.

I went from 180 to q 195 and my engine starting pinging from the extra heat.

Not all cars will do this but mine did.

But the 180 back in and the pinging went away. Of course it took 2 months to figure out what was causing the pinging since I did a tune-up at the sametime as swaping to a higher t-stat.

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Old 04-15-2007, 09:13 AM   #12
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Originally Posted by eivad1 View Post
hows does keeping it warmer make it get better gas mileage
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

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

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

Time is the best teacher. Unfortunately it kills all its students.

Bike Miles (Begin Aug. 20 - '07): ~433.2 miles

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Old 04-17-2007, 07:27 AM   #13
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Two points re. changing a t'stat.

1) Be sure you put in t'sat in same orientation as it was. It's basically a disk with hole in it, and some stuff on each side of disc. Some cars will let you put the thing in upside down, and then it won't work right.

2) Watch for a small air bleed hole in rim of the t'stat disc. Usually has a little "jiggle pin" at the hole. This is to vent air bubbles that are in the system. The t'stat mount location is usually tilted at an angle. You have to make sure the vent hole is at the high point so that the air bubbles will find it.

Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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