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Discussion Starter #1
Would changing the thermosat temperature thermostat increase or decrease mileage? The amount of fuel is controlled by the ECU and once the car is warmed up, would +,- 10 or 15 degrees increase or decrease mileage. I am thinking that combustion could be a little easier, especially while the car is warming up, and it's such a small difference that the ECU might not go into limp mode.

When a gas car is warming up, they run in cold loop mode and run rich to warm up the car because the o2 sensors aren't working well yet,
 

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5 degrees will not have a meaningful effect. 15 might. The difference between a hot and cold thermostat is the temp at which the thermostat opens. It's a spring loaded valve that expands and contracts at various temps. I don't think this will effect engine warm up by much. Even 2 thermostats might have a 5 degree difference between them. When you're driving in the summer vs. winter there's more than a 5 degree difference.

IIRC, the TDI is about 190-195. This is hot compared to a gas car, they might open at 150-160. Unless you have a pumpe duse, you have no o2 sensors and they have no direct role in fuel metering either.

IMO, if you go too low the engine isn't running right, if you're too hot the coolant fan goes on and you put load on the alternator and other bad stuff
 

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I think maybe if a performance thermostat let you block off the grille openings. You would want the minimum size opening to provide sufficient airflow to the intercooler and radiator. Anything else could be taped off to provide better aero.

It would be slighlty cooler, the above should raise the coolant temp slightly but it should be regulated by the thermostat overall. This "performance" would have a larger opening to let coolant flow through it with less resistance. The idea is to maximize the efficiency of the coolant system, in other words, let coolant absorb heat from the engine where it's needed and let coolant flow more efficiently where it's needed. Unforunately, I'm pretty sure that the engineers who made the block have already done this study with 1000x better results and knowledge that anyone short of an engineering house could achieve...so all you could do is clean up casting flaws or rough edges. Maybe a larger radiator could also help.
 

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Discussion Starter #4
So what you are saying is that the coolant won't help but increasing the efficiency of the radiator so you can block off the grill will? Isn't that the same as changing the thermostat?
 

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Kind of, the overall idea is to improve the aerodynamics of the car by blocking off most of the front grille. Adjusting the cooling system is just to keep the car at a reasonable temperature. The thermostat only controls the flow of coolant to the radiator and helps control the temp of the coolant.
 

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It's fun to think about ways to save gas, but slowly pressing the accelerator instead of quickly stomping on it is still number one.

Then carrying minimum weight.

Then using just enough gas to get you to where you want to begin slowing down. No point in racing from stoplight to stoplight.
 

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Discussion Starter #7
Cool thanks, it was just an idea. I suppose that other than adjusting the fueling through the ecu, there's no way to lean the fuel out like this.
 
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