I agree, 20 degrees in one minute is a pretty high rate of change, I would definitely say that if it is rising that fast, then the thermostat is still closed at that point. What thermostat do you have installed ? If it’s a 195, you’re going to have a tough time keeping the motor at 180. 11/12 are the jumpers to be avoided, they’re connected to ign and ground respectively
The DCC depends on a 12 degree rise through the engine and if the thermostat is slowing the coolant flow, it will be off by the ratio of full flow vs the thermostat restricted flow. In other words, if the thermostat is limiting the flow to 50% of normal, the temp will be off by 12 degrees. The fact that the dcc monitors the engine inlet temperature in lieu of the outlet temperature is what makes it a little trickier to set up, but it’s the correct way to do it. I’ve had a few customers monitor the engine output in lieu of the input and this makes for a system that’s easy to set up, but one of the main benefits, the fan not running at highway speed, is traded off. The hysteresis mentioned is also true, I’ve seen it on customers data logs. The constantly spinning mechanical fan tends to stabilize the thermostat to some degree.
There are a couple of options. One is that you can use the u/d option to simulate the airflow of the stock fan below the thermostat temperature, the other, and a better method would be to go to a 180 degree thermostat.
The most common error in installation is mounting the probe from the front of the radiator, those fins tend to be off by about 20 degrees. A second issue is caused by the fact that the fin density varies from one radiator to another, so the probe doesn’t always fit perfectly. One of my customers figured this out and found that using a small pair of needle nose pliiers to form the fins around the probe solved the problem
The third most likely, but probably doesn’t apply in your case, is a bad chassis ground. The temp sending unit is referenced to the engine block, while the gauge is referenced to the chassis, so any difference shows up on the gauge. A good test for this is to let the temp stabilize with all of the accessories off. Turn the lights and everything else on and watch the gauge over the next 10 seconds. If it moves, there’s a problem.
Fourth, the lower tubes on a cross-flow are the first to clog, if there’s no water flow, the fin temperature will be off by a large amount.
Finally, on a high power fan, if the sensor is too close to the fan blade, the heat is pulled down the tube away from the sensor, so the corners, rather than the middle of the radiator are optimum.
) so you know what the fan is doing at these high temps. Is it even turning on? Is it running at full power? Also get the remote temp adjuster for inside the car, it really saves you the grief of contantly messing with the jumpers under the hood to find your preferred temp setting, especially if you're having issues. I would also recommend a 180* t-stat, the DCC is designed to work with one. By the way, what temp do you have the DCC set for?
