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I am driving Nissan Sunny Diesel in pahalgam Kashmir with a temperature range of -20 to 40. My car is heating slowly. I have changed the thermostat also. But after driving the car almost 30 kms the temperature gauge still shown -30 in dash board. Plz suggest.

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  • Please explain whether the engine is not really heating up or the temperature gauge is just not reading properly. If it's not heating up, then the problem is the thermostat.
    – jwh20
    Commented Dec 5, 2022 at 3:19
  • With temperatures well below freezing, a new thermostat in place, and the engine not heating up, this may be a situation of blocking off all or a good portion of the radiator to allow the engine to warm up. Extreme cold temperatures can justify radiator blocking. This presumes correct antifreeze amount and the cooling system is maintained.
    – F Dryer
    Commented Dec 6, 2022 at 22:32

2 Answers 2

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After 30km your engine and coolant should be warmed up. I'm sure your engine will be warm, what you need to do is check your radiator, be careful not to burn yourself doing it. A good test is whether your heater works after 30km, if it does you're probably okay, if it doesn't you have a more serious problem.

If your radiator is still cold at 30km and your heater is still blowing cold air then you probably have a problem somewhere in your cooling system:

  1. Coolant: In extreme cold it could be that your anti-freeze isn't strong enough and your coolant has frozen. I had that happen to me, my coolant froze in the hose, which then exploded due to the pressure
  2. System block: there could be an obstruction in the cooling system which is stopping it from circulating
  3. Bad water pump: the coolant pump may have failed, or it's not being turned by the belt
  4. Failed coolant thermostat: there's a valve that keeps your coolant circulating in your engine until it heats up to a certain level, if that fails then it will stay open or closed, if it stays closed then your radiator will never heat up

I'd start with checking your coolant and go from there. If your radiator is warm after 30km and your heater is blowing hot then it's one of these things:

  1. Bad temperature sensor: there's an electrical device screwed into your radiator which reads the coolant temperature, it may have broken or the wiring to it is bad
  2. Broken coolant gauge: it could be that the gauge on your instrument panel has gone bad and isn't registering changes in temperature
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I'd lay money on it being a bad temp sensor ... typical for them to fail and show the low reading. These are easily tested, too. The output is linear. As heat is applied, the resistance goes up (or down, depending on the sensor). You can usually find the scale (temperature vs resistance) online for your specific vehicle. If not for your specific vehicle, manufacturers usually have the same scales over their line of vehicles, so if you can find it for one, you can find it for all.

Realistically, all you are truly looking for is for the resistance to change as temperature changes. Pull the temperature sender out and check the resistance. Heat the sender up and check the resistance again. It should have changed. If it doesn't, it needs to be replaced. You shouldn't have to heat it very much to see the difference ... even 10°C should see a change in resistance.

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