I put a temp gauge on the hot line of my 98 5.9L Durango (46RE). It has the factory tow package with the supplemental oil cooler on it.

Around town or even back and forth to work (12 miles on the high way) its not uncommon for the temp to read 200-230. The other thing I have noticed is that regardless of air flow etc – once it reaches 200+ its gonna stay there until you shut it off for a while.


This is just normal driving and given the light load its under at the time, these temps seem very high to me. I don't have a sensor in the pan but expect correlative numbers (probably ~80 degrees less based on experience with other vehicles where I installed two sensors) I double checked the lines and they are not tangled up with the exhaust or anything like that. When I bought it ~6K ago I put in a new filter and flushed the system with 14 qts of Valvoline ATF+4.

I checked out the radiator, external cooler, condenser they are not plugged and are free flowing. The fan shroud is intact and the fan clutch is good. The engine stays right at 185 (on the in dash gauge) no matter what. In disbelief of the high numbers I ran a separate ground wire to the sending unit bung and even swapped the sending unit and gauge with one I had in my Jeep. Both vehicles read in the same range as they did before.


When I had the sending unit out I double checked the pump and it seems good too.



I want to tow with the Durango but am concerned at the high temps so I want to get this figured out before i have a problem.

What tranny temps are others seeing in their 5.9s?

 

1. That cooler is a TRANSMISSION cooler, not an "Oil cooler".

2. It shouldn't be that hot! Replace the T-stat with a 180 degree F one.

3. Bung means *******, redefine your response.....

4. Coolant runs in between the T-stat and the bypass back into the water pump. As the heat rises it brings in cool coolant from the radiator, however is also again recirculating the HOT coolant through the bypass, so it is common to see higher temps between the T-stat to the return through the top radiator hose. However you should see the T-stat setting temp in your return hose and full flow after about +10 degree's over the T-stat setting point.

Meaning, if you have a 180 T-stat then expect 180+ coming back into the radiator (high side return tube) from the T-stat neck into the radiator. Full flow should be well after the set point of 180 for instance. OEM is 195 degree F.

5. Trans temp should be around the same temp as engine OEM.

I would suspect the T-stat and replace it with a 180 degree F, I say this because 180 is perfect with the motor, just not with emissions, as well as better with your heads. You will have a colder heater, but better for the motor. Personally, I would get a good solid T-stat with a good gasket at 180 F.

 

I think he is talking about his transmission fluid temp, not the water temp being high.