Just picked up my 04 5.9L Cummings Diesel about a month or so ago and I am still new to all of this... so bear with me.

Tax refund came in first off..

I know I need a new T-Stat, since the one I has it stuck open I believe (no heat in the car, barely gets to operating temp)

My question to you.... would you rather opt for a higher temp T stat, or lower than stock? I figure, might as well try and do some sort of upgrade while I am fixing the issue.

Another question, would the motor perform better at a higher-then-stock temp, or a lower-than-stock temp? Sorry if I am rambling on with random questions.

 

I'd go with a reg. stock one IMO.

 

Thanks for the reply! I was basically wondering if putting a "hotter" or "colder" Tstat in would improve performance since I was replacing the OE Tstat anyways.

 

Colder heater temperatures are usually caused by higher diesel efficiency.
They don't develop heat as a gasser would do with no load conditions.