Engine/Transmission (1998.5 - 2002) Fuel Mileage and Thermostats

[rblomquist]

Can someone explain to me why they'd see better mileage with a colder thermostat? And if better fuel mileage is had by cooler thermostats I can't figure out why it'd be better to have less fuel mileage than slightly more emissions with a colder running engine.

 

[NIsaacs]

Not sure where you are getting your info, the Cummins like's to run on the warm side. I like the 190 degree factory one, seems to be just right. Anything less than 180 is too cool, and will induce more engine wear.





"NICK"

 

[OTRPU]

My 99 never gets to 190 without a load. And with a load it barely gets past mid guage, like a needles worth. Got the stock T-stat what came in it, should I be changin it?



Cheers,

Steve J

 

[nuv22]

My 99 will run around 180-190 neadle fluctuaction but it never goes over the middle mark. does the auto transmission make a difference in the teperature?

 

[rblomquist]

Not sure where you are getting your info, the Cummins like's to run on the warm side. I like the 190 degree factory one, seems to be just right. Anything less than 180 is too cool, and will induce more engine wear.





"NICK"

About 1. 5-2 years ago there was a big push on the board that got folks with newer 2nd gens changing their 190 stats to the cooler one that are in the earlier year trucks. A lot of people were claiming better mileage after they changed to the cooler thermostats.



Not sure I understand your hard engine wear statement in regard to slightly cooler thermostat. These trucks came with the 180-185 t-stats for years and from what I heard the reason for the change to the 190 was strickly EPA driven.



A lot of new cars and trucks are running stock t-stats in the 200+ range which is also I believe directly the result of emissions requirements. The hotter an engine runs the more pollutants it burns off I guess is the theory. Remember cars back in the day came stock with like 160ish t-stats and when the enviro stuff started to kick in they started coming with hotter and hotter t-stats.

 

[RustyJC]

For a given BHP output, if one is going to keep the coolant temperature at 180 degF instead of 190 degF, more BTUs (i. e. , thermal energy) have to be rejected through the radiator. Where does this extra thermal energy come from? Combustion of #2 diesel. If the energy is being thrown away through the coolant, it can't push down a piston or drive a turbocharger.



Rusty

 

[mcoleman]

Gas burners will pick up a considerable amount of power with the 160 thermostat. And I've never lost or gained anything on fuel mileage when I changed to the 160 from the 195 on a gas rig. My truck came with the 180 and I replaced it with a 180. I doubt if you will see any mileage difference between a 180 and a 195. But I like starting 15 degrees cooler when I'm towing hay in the hills.

 

[mhenon]

For a given BHP output, if one is going to keep the coolant temperature at 180 degF instead of 190 degF, more BTUs (i. e. , thermal energy) have to be rejected through the radiator. Where does this extra thermal energy come from? Combustion of #2 diesel. If the energy is being thrown away through the coolant, it can't push down a piston or drive a turbocharger.



Rusty

Rusty, That's what I thought. Within reason, the hotter an engine runs. . the more efficient it is... no? I would think those guy's going to a cooler thermostat would be the ones towing/hauling heavy in the summer (like. . Arizona at 108F).



Mike

 

[RustyJC]

Rusty, That's what I thought. Within reason, the hotter an engine runs. . the more efficient it is... no?

Mike,



Within reason, yes. In engineering terms, one of the research and development processes we go through with a new engine model is to perform a heat balance analysis. What this means is that we have to account for every BTU that goes into the engine in the fuel - it either comes out as BHP or as losses. The sources for heat losses include the jacket water cooling system, the lube oil cooling system, the exhaust, heat radiation from the engine itself, etc. In order to hold the coolant temperature at a lower temperature, more heat has to be rejected from the coolant system's heat exchanger (e. g. , a radiator, shell and tube heat exchanger, plate-type cooler, etc. ). This is somewhat (but not completely) offset by lower radiation losses from the engine.



The results of the heat balance analysis are what we use to size the radiator, lube oil cooler, etc.



Rusty

 

[Rman]

Rusty,



If this energy is thrown away to the coolant, would perhaps this allow for more energy to be introduced and yet still keep the operating temperature within tolerance? i. e. injectors, turbo, NOS, propane, etc... Just curious

 

[RustyJC]

Yes, increasing the size (really, the capacity) of the cooling systems (along with other modifications) can allow more brake specific output (BHP/cubic inch) for a particular engine design.



To illustrate, we introduced an engine design in the 1930's - a Vee-type, natural gas fueled, spark ignited integral engine/compressor with a 14" bore and 14" stroke. The original version of this engine produced 100 BHP per cylinder at 300 RPM with a fuel consumption of about 9800 BTU/BHP-hour. The latest version of this engine still has the 14" x 14" dimensions and produces 225 BHP per cylinder at 330 RPM with a fuel consumption of 6800 BTU/BHP-hour. Even though the latest version of this engine is far more thermally efficient (i. e. , has a better brake specific fuel consumption), it rejects more heat in gross terms (BTU/hour) to the jacket water and lube oil cooling systems than the original version of the engine because it's producing far more BHP.



Just to illustrate further - does anyone remember the millions of $$$$ spent on research within the last 10-15 years on the ceramic-based adiabatic engines? The engineers were trying to come up with engines that didn't even have cooling systems! Why? To eliminate this source of thermal energy losses, thus making the engines more thermally efficient.



Rusty

 

[JEccles]

hey, hey Rusty i just bought a house in cypress, its pretty much at the end of fry road. sounds like a mini-truck meet for the cypress chapter is in order!

 

[RustyJC]

Sounds good. We're in the Louetta Road/Grant Road area.



Rusty

 

[Rman]

I agree Rusty, the internal combustion engine is grossly ineffiecient in terms of thermal efficiency.

 

[Un-Hemi]

Yeah, they're not very efficient, but they haven't been eclipsed by anything better at converting dead dinosaurs into motive power for over a hundred years.



In other words, it's the best we have.



Long live Internal Combustion!

 

[Rman]

They most certainly have... . it's just not as cheap and readily available as dead dinosaurs! I still think the oil industry plays a large part in supressing newer technologies... now that fuel is getting this ridiculous parhaps that supression may be lifting.

 

[Hohn]

My efforts to warm the engine....

Gents, THIS is why I have been looking at ways to keep more heat in the engine.



See, the majority of my driving is home to work to home. That means cold start, short trip, park, followed 9 hours later by cold start, short trip, park for the night.



This time of year in Cheyenne, we're getting low 40s and someimes 30s at night. Not too much warmer during the day.



So I wanted to start examining ways that I could better manage the engine's temperature-- first, make it warm up faster, and second-- have it run at a hotter average temp.



My first effort was just attached cardboard to the inside of the billet grille. That reduced thermostat cycling.



Then I removed the fan. This helped a LOT with warmup, and further reduced thermostat cycling (you know, the variance from 160° to 190° that seems to happen all the time).



With the grille blocked and fan removed, the engine still won't run over 190. So then I began selectively blocking off parts of the radiator. This would allow temps over 190, but seemed unpredictable, so for now, I'm not going to block the radiator itself until the temps get colder.....



Wishing for a 210 thermostat,

Justin

 

[RClark]

Correct me if I'm misyeaken but from what i get from this thread is to use the 190 that came with the engine.

the only advantage i've noticed with the 180 is that the fan does not come on as often.

 

[Hohn]

That's my take. I don't think a 180 offers any real benefits because once the T-stat is open, it's up to that rad and cooling system to determine operating temp. I higher t-stat should keep more heat in the engine and make it more efficient.



jlh

 

[OTRPU]

I'm not sure of which thermostat I have, but the coolant temp seems to hang out around 170 to 180 on level runs. Have seen it get as high as 205 or so when climbing loaded. Don't know how much more efficient these things can get but I just hand calculated my last tank running from Lakewood, CO to Gretna, NE Flying J. . . I can't believe it. . . figured it twice. . . how's 28. 8 sound? Think I'll call myself a lier.



Cheers,

Steve J