I've had a Scan Gauge II in the truck for the last 3+ years and usually have it showing ECT EOT FICM main power and volts. For all that time, my numbers have been normal until last month. With the engine up to temperature (ECT at 190 or higher), my EOT is lagging behind - sometimes 20* cooler. I've also noticed the EOT jumping around for no apparent reason.

From what I understand of the 6.0 cooling system, the oil is cooled by the coolant and what I'm seeing shouldn't happen if the engine is up to temperature. The obvious fix is to swap out the EOT sensor but I figured I'd ask the experts first. Any thoughts?

2005 dually crew cab with 105k.

 

I would be curious what your EOT and ECT are reading after a cold soak of 24 hours.

Also, have you tried swapping the plugs around to see the result?

 

Thanks Mike

Have to wait until Monday for a true cold soak and I'll check the readings before starting. Last time I checked after a cold soak they were 1.5* apart from each other. Don't recall which was higher.

Swapping the connectors between the ECT and EOT is a great idea. If the temp differential is OK when cold, I'll definitely try that. The EOT sensor is less than 2 years old. It was replaced by Ford as a source for a nagging oil leak, maybe I got a lemon!

 

Thermostat could be sticking, but you would likely see higher coolant temps than 190. Maybe partially sticking? If the sensors are good, once the stat opens your oil should go above your coolant temperature.

 

Jumping around sounds like either a bad sensor or a wiring issue.

It's the same sensor as the ECT so swap the sensors.

 

Mine did the same thing. Took off the connector, cleaned sensor pin and reinstalled with a light coating of dielectric grease. No problem after that. If it was the t-stat the ect would also be wacked.

 

I checked the temperature differential after a cold soak and they were within 1 degree of each other. I did remove the connector and cleaned it out on the pretense that there may have been some oil residual in there when the old sensor was leaking oil. Got it up to 170 degrees on a short trip yesterday with no fluctuation so I may be on to something. Gotta pick up some dielectric grease though....

Thanks all!