its getting pretty warm where i am and ive seen my temps get over 200 pulling the 5er.i checked my tstat and its a 195 degree,my local cummins shop has a 180 tstat for the cummins but they told me these engines like to be hot and running them cool is bad for fuel economy.is this true?will 15-20 degrees make a dif?

 

yes it will. 15-20 degrees of coolant temp will equate to 100* of cylinder temp, and then you may have carboning up and incomplete burn issues.
stick with the standard tstat and try running water wetter( or something similar). keeps mine just at 200 when i'm pulling up the grades.

 

Look at it the other way will 15-20 degree make a diff if it is higher?? When I tow I average 10 degrees hotter and can spike to 215-220 on a climb. I don't see an issue or anyway to cool it more as at this point the Thermostat is open 100 % and if it opened at 180 or 195 it will still be 100% open at 205 so if you are loaded it will run hotter. Yes 15 degrees cooler could reduce MPG as you could have less then complete combustion.

 

I have the 180 in kine and it runs 185 most of the time but with the warm weather here and lots of fuel on tap I have no trouble getting over 200.

 

i guess the only way it MIGHT help is if you tow almost all the time and have temps. climbing into the 215-220 range. that would bring it down into a more normal operating range

 

In the summer around phoenix, it's nothing for a stock truck to hit 200F no-load, gettin' on the freeway!

I wouldn't worry until you are at 210-220 pullin max gcwr on flat land.

Like was said earlier, it's still relatively normal if you hit 210-220 loaded pullin a hill.

Tony

 

cool thanx guys,

 

well running to cold is as bad as running to hot.poor fuel miage and will carbon up after a period of time.

 

I've been running the 180 degree for over two and a half years, mostly towing 8-9K with no problems. I just like to see a little cooler engine temps on the passes and when I am out in the southwestern desert country. I have not seen any reduction in fuel mileage, 18-19 mpg empty and 13-15 towing, about the same as with the 195. Maybe it's all in my head, but I like to see that temp guage below 200.