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Coolant temp fluctuates - thermostat or gauge?

Discussion in 'GM 6.5 Diesel Engines' started by bfourman, Jan 13, 2011.

  1. bfourman

    bfourman New Member

    130
    0
    Dec 19, 2009
    Vincennes, IN
    I did the 98+ water pump upgrade recently on my 96, reused the single t'stat crossover with a AC Delco 195* thermostat. I also removed the radiator and flushed 14 years of farm dirt out. Since I did this, the operating temp seems to fluctuate between 185-195 on the gauge. I can watch the gauge move back and forth as I drive. It's not rapid, but it seems like the thermostat can't make up it's mind. I haven't checked the sensor to see if it's reading properly, but I didn't have a problem until I swapped t'stats.

    It hasn't gone over 195*, but it has been right at or below freezing here for a while.

    I used a Delco t'stat since I had read on here about the Stant having problems. Any ideas?
     
  2. ak diesel driver

    ak diesel driver Well-Known Member

    10,040
    163
    Feb 7, 2009
    alaska
    might just be a really accurate guage. Takes alittle while for the water temps to stabilize especially if it's cold outside. also could be air in the system
     
  3. bk95td

    bk95td 6.5 nut job/addict

    2,548
    3
    Nov 26, 2008
    x2 on the air in the system. I've never had any fiuctuation with the AC Delco thermostats. With other brands it was all over.
     
  4. bfourman

    bfourman New Member

    130
    0
    Dec 19, 2009
    Vincennes, IN
    What is the best way to get the air out?
     
  5. buddy

    buddy New Member

    It will work its way out over a couple days, you usually find that after it belches is out you are a half gallon low or something like that. If its been a few weeks then may not be it, check to make sure its full of water.

    Which ACDelco stat did you use, because they have a 195 and a 190 degree for the same application.
     
  6. bfourman

    bfourman New Member

    130
    0
    Dec 19, 2009
    Vincennes, IN
    It's been several weeks. The reservoir is full to the line. I don't know exactly which one I put in, I called the local GM dealer we have an account with and got the stock replacement for my 96.
     
  7. NVW

    NVW Well-Known Member

    7,487
    165
    May 5, 2008
    Castor, AB.
    There is a little air bleed screw on top of the T stat housing, the air should have bled out on it's own by now though.
     
  8. bfourman

    bfourman New Member

    130
    0
    Dec 19, 2009
    Vincennes, IN
    Would a slight fluctuation like this cause any problems, or should I just not worry about it? I'll probably flush and fill the system in the spring to prepare for camping season, I'll try and get all the air out and see what happens.
     
  9. NVW

    NVW Well-Known Member

    7,487
    165
    May 5, 2008
    Castor, AB.
    As long as it doesn't get high I wouldn't worry, it just might be a sensitive gauge.
     
  10. Brooklyn Tow

    Brooklyn Tow 9 11 Never Forget

    3,212
    2
    May 6, 2008
    Brooklyn, NY USA
    Maybe you got a skechy T Stat......I like the Robert Shaw 180*- JMO
     
  11. tightgroup

    tightgroup New Member

    83
    0
    Dec 24, 2010
    Montreal,QC
    I would say X3 on the sensitive gauge. On my gasser rebuilts (Range rovers) I always use autometer senders and gauge. You actually will see the T stat working. The temp will reach the tstat open temp , it will get a few degrees hotter and then you see the tstat fully open as the temp decreases, slowly building up temp again. Normal ops.
     
  12. Big T

    Big T Active Member

    2,358
    12
    Sep 25, 2009
    Fullerton, CA
    Did the Heath cooling mods on the '95, but it has the dual crossover with AC Delco 195 T-stats. The temp moves around just as you described. That never happened when I had the 180 t-stats in it. With the 195 t-stats you're running it in the most efficient temp zone, but it's also right there where the fan clutch kicks in. So you bump up against the fan clutch kicking in and it knocks the temp back down. It's the constant back and forth, ying and yang with the 195 t-stats. If you don't like it, then go with the 180. I honestly have never seen any mpg difference between the 180s and the 195s. It must be a very slight difference, or really it's that the 195s were the optimal range for emissions which I really don't give a hoot about.
     
  13. bfourman

    bfourman New Member

    130
    0
    Dec 19, 2009
    Vincennes, IN
    For winter time I'll keep the 195, probably switch to 180 for towing season.
     

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