No heat but coolant at temp

Discussion in 'VW Mk4 Jetta, Golf, New Beetle, Passat TDI forum' started by luxuryrules, Jan 6, 2018.

  1. luxuryrules

    luxuryrules Member

    Joined:
    Oct 24, 2014
    Messages:
    77
    Car:
    2004 Jetta TDI
    Location:
    USA
    Odd scenario, I need help to understand. 04 BEW Jetta with manual. It's got a frostheater on it (goes on one of the hoses leading into the oil cooler) and especially lately that has been worth its weight in gold. Given the cold recently (we've been fluctuating between -10 to 10 *F), I almost always have it plugged in. The heater doesn't keep my coolant at temp, which I expect given the severity of this cold, but I can definitely see movement on the temp needle after a few minutes of driving. If I use the heater when it's 30 *F out, the needle will be around 140ish.

    The other day I had to start it in -5 when it hadn't been plugged it. Took a few cycles of glow plug and cranking it for a bit, but got running. Took close to ten minutes to get movement on my temp needle. Close to twenty to get up to temp, but no heat. Assuming the dial is accurate-ish, the car will always get up to 190 (needle is vertical) and then stop rising. That's what happened, fully warm coolant, but zero heat. None. Turning on the vents produced air current so cold it would numb my fingers in a few seconds.

    Next time I drove the car (having it plugged in), heat worked fine. I experimented with leaving unplugged for the next day, and same no-heat condition. So my question is, how is the cooling system working? Where is the temp sending unit that feeds the dash? I ask that in relation to, is it possible my tstat just never opened? I can't quite grasp how in one case I get heat and in another, I don't, when the coolant is at temperature in both cases.
     
  2. Dave N

    Dave N Member

    Joined:
    May 31, 2015
    Messages:
    71
    Car:
    06 Golf TDI BEW 09A
    Location:
    Spokane Wa
    The coolant gauge in these starts to visibly climb around 90 degrees and will be on the 190 degree mark between 115-210 degrees actual. So even though it may say 190 chances are it isn't as it can say 190 as low as 115. You can help yourself by installing a winterfront to block airflow to your radiator () and make sure you leave your AC switch off because anytime it is on one of your cooling fans will run no matter how hot or cold the coolant is
     
  3. luxuryrules

    luxuryrules Member

    Joined:
    Oct 24, 2014
    Messages:
    77
    Car:
    2004 Jetta TDI
    Location:
    USA
    Aha - so the gauge indication has a huge range of variance. I could see it's plausible that I might not have gotten about 115. But at that temp, I have to figure I would get *something* out of my vents, even if it's not real hot, but even lukewarm or room temp.
     
  4. Dave N

    Dave N Member

    Joined:
    May 31, 2015
    Messages:
    71
    Car:
    06 Golf TDI BEW 09A
    Location:
    Spokane Wa
    Remember your fan, ductwork, and everything else is cold and sucks heat away until it warms up as well.
     
    Last edited by a moderator: Jan 7, 2018

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