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Thread: faulty engine temp gauge?

  1. #1
    +50kw marks13's Avatar
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    Default faulty engine temp gauge?

    g'day so ive had my s13 ca18de for around 2 months now and noticed that the engine temp is always on 0 or sometimes crawls up to a quarter, then half hour later goes to 0. even when i give it to it sometimes i never see it go over a quarter then goes back down. tried looking for some info on how to fix it but didnt find much and i dont want to go hunting around the car and screw something else up.

    anybody know how i can fix it? whether its the thermostat or the gauge or something else?

    cheers!

  2. #2
    quack Rake's Avatar
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    A good indicator - does the heater work?

    A guage isn't usually prone to failure.

    If the heater isn't nice and hot after say, 5-10 minutes of driving, and is instead cold or lukewarm at best, I'd say the temperature guage is probably accurate, and you've got a dodgy thermostat. Happened in my old car. Fortunately, replacing a thermostat is usually quite easy, and a new one to buy is probably only around 20, 30 dollars. If it's never been done, and it's an older car, it might be worth just changing it anyways.

    Another indicator - is the guage more likely to rise up on a hot day, rather than a cold one, or when the car is sitting idle for a long period of time without much airflow to cool it down? (Parked, or in Traffic). Basically, the guage might work, but its reading will flactuate a lot, rather than more-or-less sticking to one place.

    Otherwise, if the Thermostat is known/presumed good, and the guage is just constantly dead, it may be the sensor, the guage itself, or the wiring inbetween. Sensors can usually be tested by removing them, and putting them (in this case) a container of hot or boiling water. You could possibly have it still connected to the cars wiring, to see if the guage registers. The 'proper' procedure might be to dunk it in oht water as before, and use a Multimeter to test it. Depends on the sensor.

    Being a Nissan, it's most likely Resistance based, so you'd put the MM to Ohms. In cold water, or just sitting dry, it will be cold, and should register high resistance. The hotter the water, the less resistance there should be, which the MM will show.
    Last edited by Rake; 06-09-2010 at 05:51 PM.

  3. #3
    Hands Dirty +100kw Jonski's Avatar
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    could be the thermostat. i had a hyundai sonata 04, and the temp wouldnt move at all, then sumtimes it would go from 0 to all the way up in less than a minute. decided to remove the thermostat so it wuld only stay on 0 and sold the car..

    Current cars: BMW 320i 2006, Celica ZR 2003, Falcon Ute XL 2004, Nissan Navara 2005, Hyundai Sonata 2003.
    Previous cars: Ford Falcon ute XLS 2005, Saab 93 convrtable turbo 2002, Mercedez C200 2005, Mitsubishi Triton 2001, Mitsubishi Pajero 1996, Falcon Stationwagon 1998, Subaru wagon 1982.

  4. #4
    +50kw marks13's Avatar
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    thanks rake! the heater does work after like 10min really well. in traffic it does go up to just under half (like any normal operating temp) then goes right down once i start moving. my old mans a mechanic come sales rep for a peformance exhaust company but hes always away for business. ill get him to look at it next time he is in the area, just i really want to do something about it just incase my car does overheat for whatever reason, i really want to know about it haha

    thanks mate!!

  5. #5
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    If its rising to just under half way when idling at the lights and cooling back down when driving thats not really a problem at all

  6. #6
    quack Rake's Avatar
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    Since the temp does go up sometimes, I'd say it's the thermostat.

    Quote Originally Posted by Reuben View Post
    If its rising to just under half way when idling at the lights and cooling back down when driving thats not really a problem at all
    If it's dropping all the way back down to C, then yes, it is.

    A thermostat, in any machine or appliance, regulates temperature. In an engine, it prevents water from flowing through the radiator when the water is below a certain temperature. When the water gets hot enough, it opens, allowing the water to flow through the radiator, to prevent it from getting too hot.

    When sitting in traffic, there's no airflow over the radiator to cool things down, hence the temperature going up. This is why Fans are fitted, to help cooling when sitting still, and this is why you'll almost exclusivly hear them turning on and off when the car is at a standstill or in traffic. When you're driving, there is airflow to cool things down.

    In any case, if the radiator is working too efficiantly, the thermostat will simply close again, to prevent the coolant temperature from dropping too low.

    -

    Isn't it annoying when you hop in the shower .. You turn on the tap, it's cold for a bit, then it gets nice and warm? You jump in, it's great. A minute later, someone turns on a hose to wash their car. Great, now it's too hot, fiddle the tap. They turn it off, you get hit with hot water. Ouch! Tap, all OK. Washing machine kicks in, and it's thirsty for warm water. Suddenly it's freezing. Crank up the heat. There we go, nice and.. Oop, washing machine's finished! Ouch! Now it feels like you're in a kettle. Down down down!

    In this scenario, you, the human adjusting the taps, are the thermostat. You're constantly changing water flow to keep temperature where it should be. Now, why expose your engine to all sorts of uncomfortable changes in water temp?

    -

    A healthy cooling system will do it's best maintain the coolant at a constant temperature all of the time. The guage on most cars will usually place the needle's 'normal' spot in the middle. Of course it may change slightly - On a hot day in traffic, theres every reason for it to creep a little higher. On a cool day cruising on an empty road, the cooling system can work better, and the temperature will be a bit less. But overall, again, once it's warmed up, it should sit at or around the middle.

    A broken thermostat can do two things. One, it can be stuck open, allowing coolant to flow through the radiator all of the time. This is the same as simply removing it entirely. The coolant will rarely have a chance to get up to temperature to begin with, so it will just sit on Cold the whole time. Two, it can be stuck closed, and never allow flow through the radiator, thus boiling really really quickly and cause engine damage.

    Simply ripping the Thermostat out is silly, unless you're stuck and playing bush mechanic. Imagine all of the engine's metal getting really hot, and having constantly cold water flowing through it. I don't know this for sure, but I'd imagine Metal is a bit like Glass - Pour hot water on an icy windscreen, and it will crack, because of the temperature difference. If the coolant is too cold, the metal parts of the engine will be at different temperatures, and will expand/contract at different rates/amounts, which might cause twisting, cracking or other fatigue. Engines are also most optimal for power and economy when running within a set temperature range, so running too cool isn't ideal.

    Some aftermarket thermostats are designed to open/close at a lower temperature then their stock counterparts. I know Nismo made such ones for the SR20. Ideally, these would be for track car, which is going to spend it's time racing/revving more, generating more heat than an engine in a road-going car - hence having a lower temperature threshold, to compensate. Such thermostats might also be more useful in locations with high temperatures - deserts or tropics, as opposed to the colder climates of the far north/south. Generally though, for your regular road car, I'd stick with an OEM thermostat or equivilant.


    tl;dr: Changing a thermostat is easy, and will cost you less than a tank of fuel. There is no reason not to do it.
    Last edited by Rake; 06-09-2010 at 09:40 PM.

  7. #7
    +50kw
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    Yeah I get that, I know how they work (Awesome explanation though) I was just going off the logic that his heater becomes hot within 10 minutes - because until a thermostat is opened the heater will not receive any heat, meaning that the thermostat works (Because it is far more common that a faulty thermostat will be stuck shut)

    But then again as you say its only $20-$30 to change a thermostat and is a relatively easy thing to do so you may as well

  8. #8
    quack Rake's Avatar
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    Yeah, that's true.

    But that said, every car is different, and may have different cooling circuits - perhaps some engines feed hot water to the heater core all the time, others only with the thermostat open .. Hmm. Would need to check the FSM.

  9. #9
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    That is also a good point, time for a thermostat change

  10. #10
    Hands Dirty +100kw CHKURPLSE's Avatar
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    Its definately the thermo. I had the same problem in the pulse checker and the stock thermo was well gone. If a coolant temp sensor has gone, in which it also did on mine, the car will keep trying to turn over for about 20 secs
    because there is no fuel being added to the mixture because the sensor is telling the car to not do so. Its probably a good idea to get a new sensor whilst your at it.
    1994 Nissan Pulsar- 14.982 1/4 mile...
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