2000 Ram 2500, V-10, 4X4, 5 speed manual.
In stop and go traffic temp goes past 210 and continues to rise.
On open highway temp drops back down.
Changed fan viscus drive twice, no help.
No loss of fluid.
Any ideas?

 

Since you did not state if you checked any of these things, here's my ideas:

1) Check level and condition of coolant
2) Do a coolant back flush and refill.
3) Check radiator for obstructions/cleanliness (fins).
4) Check/replace thermostat.

 

Coolant level Okay,
Fins clear,
will flush and change t-stat
tomorrow.
Thanks
chad

 

Clogged radiator. I had the same problem. Replaced the radiator and it went away. I tried flushing mine first and it never worked.

 

yeah, the over-the-counter chemical flushes they sell today are basically useless. They are 'de-scalers', and that's about it. They don't really break up any of the crap that accumulates in the cooling system, and, they rely on flow to do even that. If there isn't any flow in one area, the chemicals do nothing.

Say "Thank You EPA."

 

My truck did that when my water pump was going out

 

Didn't someone post a pic of a w/p that the vanes had completely eroded away in the not so distant past?

 

If this is a high mileage truck, I'd be looking at replacing the water pump. It's not uncommon for the water pump fins to wear down to the point where water flow through the motor is severely reduced. This is likely why it cools off at higher revs going down the highway, so radiator sounds fine to me and water pump sounds like its shot. Replace the water pump, thermostat and radiator hoses and the issue will likely be resolved.

 

Well, RPM are the same whether cruising around town in third, or down the freeway in O/D, difference being, airflow thru the radiator......

Granted, if it's the original water pump, it certainly isn't going to hurt anything to change it.

 

It cools off because of airflow. If your heater works good then your waterpump is probably working fine. Problem is at idle rpm your not getting enough flow through your radiator. If you a/c works good at idle, then your fan clutch is working properly. If you pull your radiator cap and can see a scale build up them you can be sure that is throughout your radiator. Probably wouldn't hurt to replace both pump and radiator, however the radiator is cheaper and easier to replace. That's where I would start.