Temp gauge is registering a bit low, thermostat issue
My temperature gauge has been registering a bit low for the last couple of months and the the check engine light just came on. Had on board diagnostics checked and it said there was a problem with the thermostat. Tech said it might be sticking or something. How critical is this and is it something that I can attempt to replace myself?
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There are a couple of possibilities. If you have a temp gauge in the car, is it showing normal temperature when the car is fully warmed up? If not, you could have a thermostat problem. If you don't have a temp gauge, then check the temp of the upper radiator hose with the engine fully warmed up. If it is not very warn to the touch, check the thermostat. Assuming that the thermostat is not stuck wide open, and the vehicle is at normal temperature, then the most likely causes are either a stuck blend door in the heater control box, or a linkage/vacuum issue with the heater control to the control box.
low operating temperatures is an indication of an air lock in the cooling system
gauges need the sender unit to be fully immersed in coolant to work but if they are not then the variable resistance material in the sender bulb cannot accurately relate to the coolant temperature
example if you have leak develop in a good system and you do not regularly scan your gauges like a good drive will do. it is possible that you will smell a dying engine yet when yo look at the gauge it will be reading cool to cold because the coolant has dropped to a point where the sender is no longer in contact with the coolant
use a termo laser to check temp of coolant at filler cap ,with cap off run vehicle till you have hot heat coming out of your heater then check with laser. if it reads above 140 then you know 2 things . either the therm sensor is going bad or the temp gauge is bad , make sure the radiator fans come on ,if they do and you have good heat then you have bad gauge.
If the thermostat is bad (i.e. stuck open at all times), this would allow coolant to circulate in the engine even when it is below the desired operating temperature. This leads to OVERcooling of the engine. You can either replace the thermostat as a first step or remove it and test it -- closed when cold, open when heated above 190-200F.
I would suspect either the temp guage or the coolant temperature sensor being inaccurate. The new thermostat is probably working good, or else you wouldn't have a very warm heater. If you have electric radiator fans, you might check to see if they are running all th time. Electric cooling fans should only come on when the temperature sensor reaches a predetermined coolant temp, or when the a/c or defroster is turned on. If the fan runs all the time, the engine would not reach normal operating temperature.