I had a similar situation with my Dango, it was the fan clutch. Although it seemed to be okay with the spin test, it was bad.
When I fired it up from cold after the change, I had the familiar ROAR sound, and all was good! HTH

 

Well, even though I was pretty sure my fan clutch was fine, as it had passed the "spin test", I decided to order a new one online. However, after installation, I still seem to have the same problem. At this point, I am not loosing coolant, I have a fairly new (2+ months) water pump, and a brand new fan clutch. I may be doing a full coolant flush, but I hate the thought of losing all the perfectly new coolant. I am still at a loss as to why the idle jumps up to around 900 rpm when it starts getting around 210 degrees, so any help in that department would help. Still looking to find an answer to this one.....I will keep you posted as info becomes available.

 

Idle jumps up because PCM (powertrain control module) recognize higher temperature than allowed and rise RPM to maintain enough airflow through radiator when engine is idle and/or wehicle at low speed or not moving. This also happens if temp. sensor is faulty and collant temperature is fine. Do you have some trouble codes displayed?

 

Thanks for the reply, and more importantly, the explanation of why the idle speed rises. That makes perfect sense to me now. In terms of error codes, there aren't any at this point. I will likely change the coolant temp sensor next, then probably the coolant flush after. I don't think it is the temp sensor because when it starts running hot, I can hear the coolant bubbling and such when I turn the truck off, so I do believe it is running hotter than normal. Thanks again, Durango 5.9!

 

I also think that there is no problem with sensor, i just explain why rpm jump and when There must be some kind of unusual clog somewhere...

 

After reading all the responses, I would check for the following.

1. Spin test the clutch again when engine has reached normal operating temperature. I assume you did the spin test when it engine was cold. This happened to me last week. Cold spin test, the clutch passed, but failed spin test after engine reached operating temperature! ( I can stop the fan with my finger with the engine running). Advise you NOT TO GET the severe duty clutch, otherwise, you'll lose mpg and get the loud fan noise under the hood. Bought a heavy duty clutch instead and solved my temp issues.

2. Power wash your A/C condenser and radiator by taking it to a self car wash. Could be debris clogging airflow.

3. Also, additional FYI, when your 5.9 reaches 210, the PCM will go to limp mode. You will lose power as the PCM is trying to keep the engine from working harder and get hotter.

4. Burp the cooling system. If you air trapped inside, it can cause the swinging of your temp gauge.

Is your temperature issues occurs with or without A/C running? If with A/C running, maybe check to see if your electric fan is running. I also realized that when the temp reaches 210 and higher, the electric fan will come on to assist in cooling.

 

The 5.9's are designed to burp on there own.


1999's didn't come with a electric fan, that didn't come till 2000 or later.

 

Just out of curiosity, what ratio did you mix your coolant to water??