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Thermostat Leak?

I have a 95 Nissan Pathfinder (VG30E 6 cyl.) that under-heats. I changed the thermostat which seemed to be OEM. I checked the new and old in hot water and the OEM seemed OK. I put the new one in and... same problem.

It can't be stuck open twice. I stuck my finger in the radiator then started the car and the coolant started warming in less than 60 second. It's the only test I could think of!!! It appears that it is letting the coolant leak by it. Why would the thermostat leak? I'm the third owner, so I don't know if it was ever changed. I doubt it did this from the time that it was new.


  • edited July 2007
    Why do you think it is running cool? Maybe it is running at the correct temperature, but the gauge or whatever you are using to determine the temperature is low, is the problem.
  • edited July 2007
    It is REALLY cold in the winter. I could run it for 20 minutes and it would not warm up. Of course it was 2 degrees out...

    However, the heat blows HOT when the gauge comes up to normal. Hot enough to make your hand uncomfortable like my Altima. It heats up way faster in warm weather. Still not as fast as normal. This is my second Pathfinder. Last one was in AZ, this one in PA.

    Also, in addition to my wacky finger in the radiator test, when you start it cold and rev the motor you can see coolant flowing.

    So, I'm 75% sure I know what is going on...but WHY is it happening. I can't just keep changing the thermostat. It is REALLY hard to get the bolts in!
  • edited July 2007
    Dumb question: are you sure the thermostat is installed in the correct direction? I bought a car several years ago that was running to cool, when I replaced the thermostat, the installed one was backwards, it would have been easy to instal the new one the same way.
  • edited July 2007
    The only reason that is a dumb question is because if you put a t-stat in backwards the car would over heat.
  • edited July 2007
    The only reason that is a dumb question is because if you put a t-stat in backwards the car would over heat.[/quote]

    Interesting, but wrong. If you knew what engine I was discussing you might understand.

    I don't know how the cooling system on the OP's engine is designed, but on some engines installing the thermostat backwards is possible and can cause flow to bypass to the radiator when the engine is still cold. An overcooling condition is almost always related to some problem with the thermostat.
  • edited July 2007
    Did it ever work right for you? You may have some restriction in the normal recirculation path that exists to warm the engine when the tstat is closed. This causes increased water pressure and overcomes the spring pressure of the tstat.
  • edited July 2007
    2 degrees? When I lived in North Dakota we used to have to put cardboard or a blanket in front of the radiator to get the engine to warm up enough to get some heat when the outside temp was near zero. Since the engine is heating up, as evidenced by your description of the output from the heating vent, I'm incline dto suggest that the system is operating normally.

    Or am I missing something? Darn it's hard to write answers without being able to see the post I'm answering!

    - mountainbike
  • edited July 2007
    Had to think for a second...

    I don't know if this motor is an odd design, but the thermostat is where the water returns from the radiator, it is attached to the suction tube (as I think the technical term is...). Rather than let water into the radiator it opens so it can suck water out of the radiator. I had to run this through my mind a couple times...I don't understand why if you take the cap off and rev the motor it doesn't blow coolant all over. Maybe because you keep the same volume in the motor all the time and it doesn't have any left over to blow????

    My Haynes manual only has a diagram for Nissan's 4 cyl. But I am fairly sure I am correct.
  • edited July 2007
    It doesn't work that great at 50 degrees either. Also, I owned a Pathfinder just like it in Arizona and it could get down into the 40's at night in January...that motor stayed warm.
  • edited July 2007
    My theory is that the t-stat is not seating correctly. But if the one I pulled was the original (It was an OEM part at least...)why was it doing the same thing?

    How do you make sure that it is seating correctly without having to keep disassembling/reassembling the front of the motor?
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