so wait...is it better to run at 190 or 165 like the pics above?

 

190 is more heat and possibly better mileage. A 180 for towing and power, 165's are usually only used in race cars. At least in my experience.

 

So here's my question.
At what temperature does the ecu switch between open and closed loop operation?

 

180 or 190 stat in a street vehicle

NEVER run a 165 on the street, that is a race only stat temperature.

i have never seen a record of the 'toggle' temperature, however a 180 SHOULD get you above it, if in doubt stick a 190 in and see what happens.

 

It's done on the O2 sensors. See they have heaters in them that is why they have 4 wires each.

That is where my Durango ran for the most part.

You get more power and less ware at 180 then you get at 195 which is OEM. The only reason they went to 195 was because or emissions and comfort, not for running better. This is why a 180 is good for towing. It keeps the heat down which intern creates a better HP and torque, thus more power!

Ya know my Durango always ran cold, but I didn't care because it helped keep my motor in better shape. What is a problem is the fact you are getting hot. I would replace it and also replace the T-stat housing. You can get it at the dealer for cheap. A 180 is the best for that motor anyway.

 

this is where mine sits with the factory stat in there.

 

Your Durango factory operating temperature is 195 degrees. For the modders, we like to have our trucks run a little cooler to prevent heads from cracking after many years of use at 180 degrees. If you modify your temp to run less than 180, you might not pass inspection and your PCM may throw a P1281 code that says taking too long to warm up to operating temperature.

The factory has designed a fail safe limit on the PCM to put your engine in limp mode when temperature approaches 210 degrees to prevent you from blowing the engine. You will experience crappy mileage and loss of power.

Normally by the time you creep up to 210, the electric cooling fan would be switched on to assist the clutch fan.

 

that wouldn't apply to the op since his truck is a 98 and the electric fan wasn't added until 2000, but +1 not going under a 180 t-stat

 

Mine hit 240 one day and the pcm went to a higher idle, thats all. No limp mode or nothing.

 

This safety feature may not have been offered for your 98 and possibly the 99 model. I also suspect it may not be offered if your truck did not come with the OEM electric fan. On my 2000 model and I would suspect the same for the 01-03, the limp mode feature is there.

After my truck was holding at 210F, I can definitely tell, no power at all. Felt like I was pulling a trailer. My MPG fell down to 8-9 mpg. After replacing the faulty fan clutch, this issue never came back as my truck never reached the 210F mark.