Buckshotmckee

Summertime is here so I'm think'n about changin the T-stat. I've read were some guys have installed the 180 deg T-stat (pt #3967195) instead of the 195. My question is, what kind of advantages/disadvantages can I expect? Performance, fuel mileage??? Thanks

Tye

ironbutt

The stock thermostat is 180 degrees. and the ECM monitors operating temp. on a 2002, if you were to install a thermostat other than stock the ECM will adjust fueling to try to maintain temp. If you run hot, it will defuel,and you will loose power. (info recieved from master tech at Cummins shop)Plus shop manual states 180 degree is the only recomended t-stat.

Buckshotmckee

I thought the stk thermostat was 195.

oestreich84

I am pretty sure only the 98 24 valves had a 180 degree thermostat stock. After that, 195's were installed. I know I have a 180* stat. I am kinda curious about mileage differences between the 180* and 195* though.

Flashpoint

I installed a 180 in my 02 and lets just say its a bad idea. The stat opens to early and causes the radiator to get hot ,which in turn causes the fan to cycle to often ,end result is fan runs all the time and makes for poor mileage.
Just a note ,My friendly dealer gave me the wrong stat which is why i know this.

oestreich84

It sounds to me like you had it in backwards. The 180* thermostat will make a truck run cooler. I have pulled 15k lbs in 100*+ weather and I still have not heard my fan engage.

Flashpoint

Maybe you have yours in backwards. Ok if thats how it works try taking it out completly and see what happens.Your ECM reads the temp and off a loop. Same reason some people on here report poor mileage because there trucks never reach operating temp. What year is your truck? I noticed my 12V doesnt read near as warm as the 24V.

oestreich84

Mine is not in backwards. If you remove the thermostat, the truck will run cool. I think all the 12 valves had 180* thermostats. I am also pretty sure that all the 98-02 SO 24 valves are the same. So, why would my 98 24 valve run any different than an 02 SO with a 180* thermostat? The reason why I said you might have had yours in backwards is because the truck will run cooler with a cooler thermostat. You said that your radiator was hot and the fan kept cycling. That is usually what happens when a thermostat is installed backwards. I know, I see it every fall. The only other option is you got a bad thermostat, which is a fairly common thing. I always put a new thermosat in a kettle of boiling water to make sure it opens and closes.

Flashpoint

Ok , if thats the case then take the stat out and run without one. You are not understanding what im saying. There is a set temp the ECM functions at .Yes the engine will run cooler.But the radiator will not hold or stop the heat and have time for it to cool. Thus making the thermostat on the fan clutch run all the time. You may need to check your spring on the front of your fan or check for dirt or oil in your upper most part of the radiator. Or the temps you are running in arent as extreme as they are here.Im stating what i had happen .I haul over 15k all the time down here in Texas 100+ heat. SO if you have a problem you know it real quick.

oestreich84

I have ran without a thermostat. Last summer my thermostat stuck closed when I was on a camping trip. I removed the thermostat and drove 350 miles without it in. The temps never got above 150*, and I lost about 1-2mpg. I guess every truck is different.

RustyJC

The 180 degF thermostat will open sooner, and more heat will be rejected to the radiator. That's why the thermal fan clutch kicks in - it senses the additional heat rejection.

Does anyone remember engineering efforts to build an "adiabatic engine"? This is an engine that used ceramic components and had no cooling system at all. The reason for this is that the heat that is rejected through the cooling system comes from the fuel and does no useful work - it's lost! The adiabatic engine would be substantially more thermally efficient than a "normal" engine - i.e., it would get better fuel mileage.

So, where do you want the energy in your fuel to go? The colder you run the engine, the more heat that has to be rejected through the cooling system. I'd rather have my fuel energy go toward expansion in the combustion chamber and energy to drive the turbocharger, so I'll stick with my 195 degF thermostat.

Rusty

blord

In one of my gasser books for Hotrodding big block Chevys it mentions a common mistake people make is putting in too low of a thermostat. There is an optimal termperature to support combustion (internal engine temp). I don't remember what they recommended (and too lazy to go look it up) but I suspect the Cummins also has a sweet spot. Since my 06 has a 195 in it, I would surmise this is where it's at.

MKELLY

My 98.5 came stock with a 180* stat and that's what I replaced it with. I too wondered about the 195*.

boostjunkie1

These engines run better with the 195's! Cummins would not put them in there if it wasnt the case. Remember, Cummins has a vast array of tests and procedures that these engines go through waaaaaaaayyyyy before they ever get to our hands. Trust the engineers on this one.

Now a GASSER is another story, but there is still a limit. SRT4's love the 180 t-stat, over the stock 195. I have dynoed both on the same day, car at running temp and have seen 2-5 hp gain on the dyno with the lower t-stat . Now on the road it makes even better performance and economy gains. Put a 165 t-stat in and you will never see full boost (If stock) because the computer tells the car to lower boost levels because it dosent think that the car has reached proper oil temps to allow for such power !

SO------Stay with the 195 t-stat. If you are thinking cooler then run a water mist system into the combustion chamber to help densen the intake charge.

big jimmy

As a side point, a diesel runs most efficently (but not emissions wise- cooler = better emissions) at around 215*.
I am not second guessing cummins here, but a hotter running diesel will perform better, as long as it is not, as mentioned above, fighting other criteria. Also, there may be issues within the cooling capacity design inside the engine that require something less than 215*.
Otherwise, the engine is tuned to get past an emissons standard, which is not always a bad thing.
So the choice they make is a balance between performance (215*) and emissions (something less than 215*)

My '97 powerstroke ran great with a 215* stat, and maybe because the electronics were less sophisticated the hotter stat was not a problem over the OEM.
For some reason cooling was never an issue with the Navistar. Yet I am hearing it enough (and experiencing it firsthand) with the 5.9 to know they dropped the ball somehow in the system design. Or maybe its just my fan clutch- have not ferreted out the problem yet.

Jimmy