# funky coolant temp gauge



## jamesd3rd (Jun 10, 2004)

I have a '93 Altima GLE that seems to have developed a new issue. Over the last couple years I've put more money into it than I care to mention but I just don't want to deal with car payments right now. Anyway, that's another story. On with the Question. For years the blower motor has not been working and I know from this forum that the fan switch is notorious for failing because of a resistor. Even though my fan switch does not work, I can still feel air coming through the various vents when I turn on 'Auto' or 'Econ'. And I can still direct that flow by using the different buttons on the panel even though the fan speed cannot be regulated.

Now here comes the wierd part, when the system set to 'Econ' and I crank up the temp, I notice the coolant temp gauge will also increase. It will often reach the mark before entering into the 'danger zone'. When I lower the temp, the coolant temp gauge drops. I haven't tried this in 'Auto' mode but I suspect the same thing will happen. At first I thought it was a fluke so I repeated the process about four times and each time, the same thing happened. Increase heater temp, temp gauge goes up. Lower heater temp, temp gauge comes down.

I was always told that if your engine is showing signs of overheating, turn up the heater. In my case, when I turn up the heater, the engine appears to be overheating. What's up with that?


----------



## jserrano (Oct 27, 2004)

First off, and going by your description, you have an Automatic Temperature Control (ATC) unit. Many of us have the manual temperature control unit. The ATC units don't have a blower fan resistor for fan speed control. Instead, they are controlled via a fan control amplifier. In AUTO mode, the fan control will be gradual so you won't initially feel much air blowing. And if the engine temperature is very low, then it will be delayed even further. Your system has self-diagnostic built-in. You should reference the service manual on how to check the entire ATC system via diagnostics.

But the engine overheating problem has more urgency. It seems to me that the radiator cooling fans might not be 'kicking in' automatically . Do they come ON? How about when you turn the AC switch to ON? Overheating problems could be a couple of thing, like the thermostat is getting stuck, the radiator cap is bad, the Engine Coolant Temperature (ECT) has issues, etc. First step though is to make sure that the radiator fans are working.

Let us know then we can continue troubleshooting...


----------



## jamesd3rd (Jun 10, 2004)

jserrano said:


> First off, and going by your description, you have an Automatic Temperature Control (ATC) unit. Many of us have the manual temperature control unit. The ATC units don't have a blower fan resistor for fan speed control. Instead, they are controlled via a fan control amplifier. In AUTO mode, the fan control will be gradual so you won't initially feel much air blowing. And if the engine temperature is very low, then it will be delayed even further. Your system has self-diagnostic built-in. You should reference the service manual on how to check the entire ATC system via diagnostics.
> 
> But the engine overheating problem has more urgency. It seems to me that the radiator cooling fans might not be 'kicking in' automatically . Do they come ON? How about when you turn the AC switch to ON? Overheating problems could be a couple of thing, like the thermostat is getting stuck, the radiator cap is bad, the Engine Coolant Temperature (ECT) has issues, etc. First step though is to make sure that the radiator fans are working.
> 
> Let us know then we can continue troubleshooting...


Both fans come on regardless if the A/C is on or not. If the thermostat was stuck closed, why would the temp rise when the heater is turned up and drop when the heater temperature is lowered? Shouldn't the gauge drop even a little bit when the heater is turned up? If the radiator cap is bad wouldn't I see coolant or steam coming from around the cap due to loss of pressure? My coolant level doesn't seem to be dropping.


----------



## jserrano (Oct 27, 2004)

Ok, I took a closer look at the electrical diagram. To me it seems like the ATC controller, which share the same thermal transmitter (coolant temp sensor) as the one for the temp gauge, is actually loading that signal down. In other words, the ATC is causing a false reading. The true coolant temperature could not be changing that fast with just the simple change of temperature controls on the ATC. If that was the case, you'd also see it reflected on the actual Engine Coolant Temperature (ECT) sensor. Putting a DC voltage to the ECT sensor would confirm that fact since it should change instanteanously if actual coolant temperature changing so rapidly. But like I said, I can't see how temperature would move up and down with a simple knob.

So there is really no need to be concerned if the actual coolant temperature is not rising.

Also, it is very common for the thermal transmitter connector to become quite loose. You might want to tighten that up a bit to see if anything changes.


----------

