[18Rowdy54]

I have what I think is a weird one. Got a Dash Command Scanner to keep an eye on things while driving. While towing this weekend things just got plain weird. Pulling Heavy over 8000 lbs I used the Tow Haul mode and the truck preformed great. 6 Hour drive through moderately hilled 2 lane highway.
My ECT (Coolant temp) got as low as 131. When this low my egr would read 0% over the next 1-5 min my temps would climb back to 160 where my egr would read somewhere around 5-17% Then the ect would slowly drop back to 131 then the egr would close and this cycle continued. Worse of all my oil (eot) stayed consistently around 239-246. The engine ran strong all day. When I dropped the trailer and headed home I turned off my tow haul and the temps were consistently as follows:
ect (194)
eot (210)

also the trans temp never got above 177
Why would my ect be hotter when in tow haul?

Does the tow haul mode keep coolant colder to help cool trans?

 

[Evil Eye]

It sounds like you have a ECT sensor going bad (way too low of a reading for coolant temps while operating) OR a bad thermostat that is sticking open. The tow/haul had less impact on your temps than dropping off the trailer. Without that extra weight, your engine didn't have to work as hard and that's why you had more normal temps. Your oil temps were getting pretty warm at 246* (253*F is where it start to defuel), so you might consider performing the delta test to see if your oil cooler is starting to clog.

 

[18Rowdy54]

my delta averages 13 degrees

 

[stoverjoe]

ECT seems unrealistically low even if there wasnt a t-stat and the ambient temps were below freezing.

 

[18Rowdy54]

can you steer me in the direction of posts for changing this sensor?

 

[DMc]

Before spending any money you could swap the coolant and oil temp sensors. If the low temps follow the sensor to the oil, then you'd know for sure it's hosed. The coolant sensor is next to the t-stat. The oil sensor is next to the oil filter. Do some YouTube searching and you'll find video how-to's!

 

[jokester00]

First, compare your EOT and ECT sensors before starting the truck after it sits for 24hrs. They should be less than a couple degrees from each other. You could still have a bad sensor, but this is a good sanity check.

-jokester