I've seen in this forum and others about how the coolant temp runs higher after doing a coolant, thermostat or radiator replacement. I saw a lot of debate as to why, although trapped air in the engine is suspected. Yes, that is the problem, as I had it happen too, and here is what I found to do to correct it fairly easily.

The refill must be done slowly to allow the trapped air to come back out the filler neck and through the internal air relief (jiggle) pin into the upper hose. The first time I added the new coolant and water, I poured it in quickly and saw that I still needed another gallon or so to complete the refill, but the radiator was filled. Upon start up, I noticed the temp rising faster than previously and it went over the usual 190 degrees and stayed around 210, but fluctuated. I tried letting it cool down twice to draw in from the overflow reservoir, but nothing changed. After letting it cool down, I drained it all out again (removing the radiator cap to let in air as it drained). When I added the coolant/water back in, I poured it in very slowly, with a few pauses, and was able to pour 95% of it all in. The temps were fine after that, and the reservoir topped it off after the initial cool down.

Refilling slowly is the trick. Plus, the truck should be on level ground or the front end perhaps a tad higher, to let the air rise through the jiggle valve.

I've read elsewhere where this problem is inherent to the coolant flow design of the Dodge diesel 5.9. Some have felt it is because the upper radiator hose, and radiator inlet, is about the same height as the top of the engine, rather than being higher (as is usual) so as to allow the air to rise out of the system properly. Perhaps this is why.

Hope this helps those who have had this coolant refill then the overheat problem.

 

I was fortunate to find a tool at the swap meet cheep that you hook to your air compressor and pull a very good vacuum hoses are collapsed to the whole system then you shut these valves and put a siphon hose as part of this tool in the coolant and water mix are added from the vacuum created and it seems to fill all the voids and eliminates the problem. Big problem on the jeep Cherokees as well as or Dodges. Just a thought. ED

 

I remove the heater hose located toward the rear of the head. Have the hose plugged, and an extended hose off the hard line that is held up with a bungi strap..... that or I road test to a driveway down the street that is about a 15% grade. Nose up, run in park about 2000 rpms for a few minutes. Burps em everytime.

 

heater hose trick or pull the temp sender out, fill till coolant comes out replace sender, finish topping up, NEVER had an air issue