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Temp. gauge reading too low.

QG18DE 
6K views 16 replies 7 participants last post by  BeOhSix 
#1 ·
So the other night, after driving back home from my parents house (about a 40 min drive), I noticed that the temp. gauge in my car was reading lower than it should have been for driving that long. The car did not drive any differently, or do anything else that I could notice out of the norm. It did it again earlier today after driving back from work (30 min drive). It's completely random when it does it, and it doesn't stay like that for long periods of time. It usually goes back up to where it should be reading. I talked to one of my Sentra BFFs about it, and he seems to think it's the temp sensor going bad. This would make perfect sense. I was just wanting some other opinions on the matter.

This picture is after driving the car for 30 min, and it randomly dropping to this level.

 
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#2 ·
Was it cold out?

A couple of days ago it was 50F over here, and I got on the highway and the temp gauge just stay down all the way down the whole trip.
Mines does it whenever its 50-55F, then it goes up after I get off and start going through stop and go traffic.
The strange part is that on the expressway I downshifted to 5th up to 90mph to see if it would heat up, and it didnt...
 
#4 ·
it could be your sensor or your your thermostat is stuck open

one or the other

if your signal is going bad your needle will move like that but if your thermostat is stuck open when stopped it will reach normal temps but when you drive it will cool down a bit
 
#5 ·
If it is the thermostat, and the motor is actually cooling down, is that something that I should be worried about very soon. I still have to drive my car to work, and while it doesn't do this constantly, I don't wanna make a simple problem into a serious problem.
 
#6 ·
If its your thermostat its not a big thing.
If you want to check something when you will drive your car for like 20 30 min check the upper and lower radiator hose one ahould be more hot than the other one if the are the same temps your thermostat is stuck open.

Did you have any check engine light ob???
 
#7 ·
I felt the upper radiator hose earlier before work, and it was pretty hot. Someone told me that if its hot then it's not the thermostat? Not sure how much truth there is to that though. My ses light has been on for years because of an o2 sensor lol. I'll probably have to codes checked at my buddies shop sometime this week.

I'm still thinking that its a sensor though. The car heats up to the normal reading on the gauge and it takes 30-40 min for the gauge to read lower, if it even does.
 
#10 ·
Did you check the lower hose to see if she was cooler then the upper one
 
#11 ·
If it was throwing a code, then it was the temp sender. The 2 wire one going to the ecu. It was a closed loop code correct? If so replace the thermostat, and bleed the coolant system and you will be fine.

This is random, but how many miles are on your car/engine? Mine had 195k and never had any issues before the sr swap.
 
#14 ·
DTC P0128 THERMOSTAT FUNCTION

it could be your sensor or the thermostat

just check the upper and lower hose when you will return home. check the lower and upper if they are the same temp, its your thermostat, if they are not the same heat change your sensor
 
#16 ·
I dont know why but many check engine code give 2 or 3 sensor to check because they work together so in this case the thermostat and the ect sensor work on the same thing
 
#17 ·
I would lean more towards your thermostat being stuck open. Easy way to rule out the ECT is to unplug the sensor and take resistance values of it with your multimeter starting from cold start and letting it warm up. the resistance value of the temp sensor should change. Compare the resistance values to a chart found in the FSM. To check the thermostat you can take the thermostat out and see if its open cold. Then boil some water and stick it in it should open. Then take it out of the water and let it cool down. See if it closes.

Also regardless the upper radiator hose is always going to be hotter than the lower one. Remember guys the coolant is flowing through a heat exchanger. The only reason they would be the same temp is if the radiator fins were clogged which would cause an over heat condition.
 
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