How cold is to cold?
 

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.:humm:

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.