Whats the cause ?

[c.moo]

This is on b -body , 383 , new cooling everything . Runs hot going up hill and cools down going down hill are on flat road . Seems under load it gets hot . Thanks

 

[1 Wild R/T]

Try adding a few degrees of timing...

How big is the radiator? Aluminum or Brass?

Clutch Fan?

 

[Johnpat]

I agree with above post.
What's your initial set at?

 

[c.moo]

Try adding a few degrees of timing...

How big is the radiator? Aluminum or Brass?

Clutch Fan?

Dual electric fans with shroud , 26 inch aluminum radiator , have to check timing , can't remember what timing was set at , you know how that goes .

 

[Oldreddodge]

Drive downhill

 

[Jerry Hall]

I agree with timing. Your saying everything is new, but what it is you haven't said. Numerous components in the cooling system. Everyone is saying add a few degrees, but my opinion to little or to much leads to the same outcome. Timing is the easiest and most inexpensive thing to try first.

 

[1 Wild R/T]

I agree with timing. Your saying everything is new, but what it is you haven't said. Numerous components in the cooling system. Everyone is saying add a few degrees, but my opinion to little or to much leads to the same outcome. Timing is the easiest and most inexpensive thing to try first.

I agree, but I was gonna say try more first & less if that didn't help....

 

[Ccas]

Agree, check timing. What gears do you have? The bigger the gears, the more rpms, the hotter it is going to run.

What radiator? The bigger the radiator (by volume) the cooler it will run on the highway.
btw, The fans are not helping you on the highway. They are a non factor at speed unless you have a very restrictive shroud that is trapping some hot air around the radiator. But even if that were the case, that would be an issue going up and down hill.