Regarding fuel economy, I agree with the individuals that state the diesels need to make internal heat to be efficent. During my previous time spent on the ford diesel forums, I noticed that the Ford guys in the signature had 210F so I decided to go back to one of the forums and ask why they put in higher temp thermostat's. The reason is to get the "INTERNAL" temperature of the engine higher. One of the advertisers on the ford forum have a 203F thermostat and claim a 1 to 3 mpg increase which I can believe.

Does anyone know if we can buy a dodge thermostat that is higher than the stock setting which I believe is 190F??

If yes, does anyone at what temperature does the engine fan kick in. I am assuming they simply use a temperature switch to activate the engine fan.

 

My fan locks up at around 210'F. You definately wouldn't want to run with the fan locked it would negate any benefits of the hotter thermostat, but it should help with fuel economy if the fan isn't locked up too much.

 

The fan could be an issue, I think aftermarkets are availible. I heard the 6.7 have a higher thermostat temp. I am trying to confirm that, and if thats true then the fan clutch would be a higher temp also. Another thing be sure to run synthetic oil with these higher temps.

 

Is the fan either on or off, or does the truck have the ability to run the fan at different speeds.

If someone out there makes an aftermarket 200+ thermostat, then the next question is how to fool the fan so it only starts to go on around 210 / 215.

 

Can you explain why more "internal heat" increases efficiency? I don't see it.

 

Simple, heat burns fuel in a diesel. Basicly look at it this way, a gallon of fuel has a BTU rating, this is a measurement of the amount of energy in a gallon of fuel. The warmer the engine is the less energy will be used up to get that charge of air/fuel to ignite. There is so much cool air running through the radiator, past the block, and entering the combustion chamber the engine can never keep up unless it is really working. Look at heating your house, the closer the outside temp is to the inside temp the less energy it will take to maintain it.

 

Well said on why internal heat is more efficent

The basic engineering principle for power is this, greatest power can be acheived with the highest delta (difference) in temperature.

If the block is warmer, then the combustion temperature will be warmer, and as a result the engine will be be more efficent. This is best explained when looking at chart which shows cylinder temperature versus emissions output. I remembered seeing a great article from Detroit Diesel (I believe) which showed when you run hot, the NOx out put goes thru the roof. The engine is running very efficent, but the output of NOx is not friendly to the enviroment. I am assuming that the mileage boxes are essentially running the engine such that the output of NOx goes up. EGR has come into the picture to reduce the cylinder burn temperatures at high boost in order to avoid the NOx output.

 

"If the block is warmer, then the combustion temperature will be warmer, and as a result the engine will be be more efficent. This is best explained when looking at chart which shows cylinder temperature versus emissions output. I remembered seeing a great article from Detroit Diesel (I believe) which showed when you run hot, the NOx out put goes thru the roof. The engine is running very efficent, but the output of NOx is not friendly to the enviroment. I am assuming that the mileage boxes are essentially running the engine such that the output of NOx goes up. EGR has come into the picture to reduce the cylinder burn temperatures at high boost in order to avoid the NOx output."

precisely why they lowered the compression ratio on gassers in the early 70's

 

I had one of those 203 degree thermostats in my Ford. I didn't see any fuel mileage increase from it. It did give me quicker warmups and higher heater temps during winter, which is what I wanted from it.

 

I think our increase would actually be from our decrease we see with colder temps/winter.

 

so what will it do to egt's

 

In practical, day to day terms, I see no advantage to a hotter T-Stat. Yes, in theory, warmer is better but let's not forget that during compression the temperature inside the cylinder, rises considerably...to at least 1700*+/-. Adding 20 or 30* to the coolant/block temp isn't going to be a big factor in combustion efficiency. JMO.
For daily driving, in colder climates, a warmer T-stat will increase warmup and heater output, as stated above, but I can't see it making a difference in MPG.
I run a Cummins 180* in the summer and see no decrease in mileage and a tremendous benefit in controling hot coolant temps.

Add some HP and tow heavy, or just play hard, and coolant temps rapidly become as much a limiting factor as EGT's.

RJ