Thermostat question

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Andrew Fort, Oct 11, 2018.

  1. Andrew Fort

    Andrew Fort Registered User

    Posts:
    21
    Likes Received:
    1
    Joined:
    Sep 26, 2018
    Location:
    Missouri, USA
    My truck ('90 F350) temp gauge used to sit right between "O" and "R" on the temp gauge. The truck had to sit for a while while I was fixing it and now it doesn't even hit the "N". I'm thinking my thermostat is stuck open. It'll be a few weeks before I have a chance to replace it. Would any damage occur in that time?

    Sent from my SM-G965U using Tapatalk
     
  2. nostrokes

    nostrokes Full Access Member

    Age:
    40
    Posts:
    390
    Likes Received:
    198
    Joined:
    Oct 13, 2017
    Location:
    Colorado
    No nothing is going to happen, it'll just be running cool.

    Just for kicks, let it warm up and feel how hot the upper hose gets. It may not actually be your t-stat but a crappy gauge. The stock gauges are nothing more than moving idiot lights and never work right to begin with.
     
    icanfixall likes this.
  3. icanfixall

    icanfixall Official GMM hand model

    Posts:
    25,716
    Likes Received:
    459
    Joined:
    Apr 10, 2005
    Location:
    West coast
    You are going to be ok driving it this way. As already posted.The stock dash gauges are nothing to depend on. Install and after market gauge and report back what you find. Also NEVER use any thermostat other than the original MOTORCRAFT thermostat. They are the ONLY one that works. they are 192 degrees begins to open and fully open at 212 degrees.
     
  4. Kevo1288

    Kevo1288 Full Access Member

    Age:
    29
    Posts:
    98
    Likes Received:
    39
    Joined:
    Feb 19, 2015
    Location:
    North Grosvenordale

    The motorcraft one I got is part number RT1049... there was another one but I couldn't remember the part number of the other motorcraft one.
     
  5. Oledirtypearl86

    Oledirtypearl86 Full Access Member

    Posts:
    68
    Likes Received:
    28
    Joined:
    Sep 17, 2018
    Location:
    Whitehall MT
    The stock gauges are useless I have a 86 with a 6.9 a few years ago the wife and I are on a 1300 mile trip and on i15 in Utah and she tells me the gauge is pegged past the l So we pull over and I grab the super duper temp gun start shooting temps nothing is even close to hot we stop at the closest Napa grab a set of gauges I take 30 min to hook up the temp gauge and the truck never even came close to 225 the rest of the trip pulling a trailer with a skid steer tied to it
     
  6. IDIBRONCO

    IDIBRONCO IDIBRONCO

    Posts:
    1,961
    Likes Received:
    797
    Joined:
    Feb 5, 2010
    Location:
    edmond, ks
    Since you're in Missouri, it will be easy to tell at this time of year. When I first got my current 85 F250, the thermostat was stuck open by a piece of debris wedged in it. It had to be in the 50's before anything that resembled heat came out of the HVAC system, the heater hoses were both barley lukewarm to the touch, and the fast idle never kicked off. If don't have any of these symptoms, then it's just your gauge or sender.
     
  7. Andrew Fort

    Andrew Fort Registered User

    Posts:
    21
    Likes Received:
    1
    Joined:
    Sep 26, 2018
    Location:
    Missouri, USA
    I'm guessing it's just the gauge. The truck had warm air blowing in about 5minutes earlier and it's in the 40s tonight.

    Sent from my SM-G965U using Tapatalk
     
  8. icanfixall

    icanfixall Official GMM hand model

    Posts:
    25,716
    Likes Received:
    459
    Joined:
    Apr 10, 2005
    Location:
    West coast
    Sometimes the over temp light on the dash comes on telling us ... Sorry its too late to save your engine now... Well the switch in the front of the drivers side head is the over temp dash light and gauge switch.Its normally open till the coolant temp reaches 242 degrees. Then it will close and cause the dash gauge to peg telling you theres trouble ahead. When they fail this switch randomly closes and sets you to worry.Easy test is to remove the wire to it and ground it to metal. Do this on a cold engine to verify this. Grounding the wire will cause the dash gauge to peg. So if you ever see the dash gauge peg but feel the engine is ok just remove the wire from the big fat switch and see if the dash gauge goes normal again.
     

Share This Page