I own a 2005 G35 coupe and as soon as the car is turned on the fans kick on even when A/C is off. After driving several miles the coolant gauge starts to spike. I took my car to the mechanic who can't figure out the problem. He said there are no signs of overheating. A few weeks ago I noticed my gas gauge goes up and down. Any thoughts of cause of these problems or suggestions? I guess this is my welcome to hitting 100k miles.

 

Try a different mechanic that knows what he is doing.

 

How drastic is your fuel gauge movement? Is it something that could be caused by parking on a hill, or does it visibly move up and down pretty quickly and repeatedly? It's possible that you have a bad ground somewhere that is causing erratic electrical problems.... but that's the only real solid link between the fuel gauge and cooling issues aside from a glitched ECU.

Did you recently do any work on your cooling system or have a situation happen where your coolant reservoir ran empty before being refilled? This could have introduced air into the cooling system which can cause anomalies with the car's cooling ability as well as coolant temperature sensing reliability.

 

How many miles is a few miles? If the coolant guage is spiking, that would logically make the ecu think that the engine is too hot and kick in the fans.

Not sure why the fans would kick in even in the 1st start of the morning? the guage would spike even after 1-2 miles?

Wait until the car is cool and check your coolant level. But if the gas guage is going crazy, I'd suspect some type of ground is loose/corroded etc....

 

If your issue was just the fans coming on I'd think it was a sensor problem. Both gauges giving the wrong signals has to be a wiring issue. You need a better mechanic as in one of Nissans better trained!
Gary

 

Sensor or........AIR POCKET !

 

I'm going with Eric. Check the thermostat. If it is stuck wide open the fans will never turn off.

 

His problem is they kick in immediately

 

It's not the thermostat. The thermostat is a mechanical device that opens based on temperature of the surrounding coolant. The thermostat doesn't need or use any electricity to open and close and should have nothing to do with the fan coming on when the car starts up. The electric radiator fans come on based on the coolant temperature sensor detecting that the coolant has surpassed some predefined threshold... probably something like 190+ or so degrees F. The thermostat on most cars open at somewhere between 160 and 170 degrees F (depending on the car and what thermostat you're using). If the thermostat was stuck open, the car would just take forever to warm up to operating temperature, which would make the fans that much less likely to ever come on (assuming the coolant temperature sensor is accurately detecting the coolant temperature).

 

best thing to do is grab an OBD scanner and plug it in... make sure the scanner allows for LIVE DATA

at that point

You can see the coolant temperature. Which then you can let us know what's going on and we can give you a better analysis of what it could be.


Or take it to Infiniti and have them diagnose the situation

 

This is definite tough one, If you take it to the dealership it is bound to cost you a lot of cash if the technician starts throwing parts at it.

After looking at the wiring diagrams for my 2003 this is what I figured out. Based on your description, the cooling fans run immediately even if the A/C is turned off. The fans are controlled through the ECM which transmits a signal to the IPDM/CPU which intern sends the signal to the #1(Power), #2(Ground) and #3(Power) cooling fan relays. This occurs under two conditions, engine temperature rise or air-conditioning operation. With that said it tells me that the relays are working and they are doing what they are being told to do by the ECM, which is to close.

I would try to isolate the two systems that are telling the ECM to turn the fans on. The easiest place to start is the Cooling Temp Sensor. If this sensor is shorted, it could be sending a false signal to the ECM thinking that the engine is running hot. With the engine cool, disconnect the temp sensor and start the engine. Cross your fingers, this would be the easiest fix and troubleshooting process. If the fans don't run, the sensor is your problem, which would probably be your cheapest fix. Let's rule the sensor out and move from there.

Hope this makes sense to you. Good luck I'll check in tomorrow.

 

*Slam*

Thanks for that one. I was just shooting in the dark.