I don't know if this is a problem or not.Most of you wish for it.I just rebuilt engine before I rebuilt it always ran 180/185 now with 4in exhaust and duramax fan 155.I figured maybe just cause its been cold here in indiana.First I thought gage since it dont move but I shot it with electronic thermo gun and no matter were you shoot(engine,manifold or exhaust)152 to 158.Today was 62 degrees outside I ran 60 mile an hour for a hour with heater shut off same thing didn't get warm enough to show on gage.this should not hurt any thing should it.

 

For economy and best power you want as close to a constant 200F as you can get.
Sounds like you used aftermarket T-stats that are notorious for not working in these engines.

AC Delco ONLY.

 

Thank you for the info I will replace them tomorrow.

 

Wrong t-Stat every thing good now.Thanks racer 55

 

Good to hear.

 

I should have known better than to get it from O'reilys never had any luck with anything from there except filters.

 

You can get AC/DELCO T-Stats at Oriely's but they have to order them the only part in AC/Delco I havent been able to get there Is my brake switch

 

I probably need to clarify that.The 2 close to me have good parts but don't have employees that no there a-- from a hole in the ground.Dident want to bad mouth hole outlet.

 

My 6.2/6.5 hybrid motor runs around the same temp. I have never even looked at my t-stats the entire I've had my truck. The only time mine runs warmer than that is when I'm towing. I have never gotten double digits in fuel economy. I get between 4-8 MPG. I will definitely change my t-stats when I rebuild it next month.