Add a resistor across the two wires for the coolant temperature sensor. That will lower the voltage making the Engine Computer think the engine is hotter than it really is. Of course that is also going to create a hard start condition in cold weather because the computer won't know how cold it really is so it will give a shorter priming pulse from the injectors at cold start-up. You might want to add a switch in series with that resistor so it's only in the circuit when you're pulling the trailer.
This is overkill if you aren't having an overheating condition. I use my '88 Grand Caravan to drag a tandem axle enclosed trailer that's bigger than the van. I can't hit 70 mph down a fairly steep long hill because of the wind resistance but it does fine at 55 mpg on a flat road on a hot summer day.
As I recall, the coolant temperature sensor will measure around 5,000 ohms at around 60 degrees and 2,000 ohms at 190 degrees. You'll want to measure yours to be sure. Adding about a 27,000 ohm resistor will lower the total resistance making the temperature appear higher. Also keep in mind all sensors are different and have an acceptable tolerance. The Engine Computer tests sensors and learns their values. In this case it knows that after the engine has been off for six or more hours, the coolant temperature sensor, ambient air temperature sensor, or battery temperature sensor will all be the same temperature. When the resistance value of one of them suddenly changes, it knows it has to rely on the one that is staying constant. The computer will learn the value of the new sensor so you will likely find the fan turns on at the same temperature as before even though the resistance of the sensor with an added resistor is different.
Saturday, March 12th, 2011 AT 1:34 AM