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Overcooling...? Any ideas?

Discussion in 'Truck & Equipment Repair' started by theguynextdoor, Jan 16, 2008.

  1. theguynextdoor

    theguynextdoor Senior Member
    Messages: 308

    I have a 1998 Dodge Ram 2500, 5.9 L gas V8. Since i got it in the fall I have never seen teh thermostat pass 150 degrees F. The thermostat is rated to open at 195, so i figure it must be stuck open so tthe truck never heats up. I replaced the thermostat with the correct opening temp (195), and if anything the truck runs even cooler. The needle barely makes it onto the gague. It stops just above 130 degrees F, once in a while it goes up to 150 ish. Twice it went closer to 200 where it should be and went back down. My heater doesn't really blow very hot air...i dont know whats going on here. There are a millions reasons for a truck to overheat...but overcoolling?

    ANY IDEAS please?
  2. grandview

    grandview PlowSite Fanatic
    Messages: 14,609

    What kind of fan is on it? Try the old cardboard trick see if that works and if it heats up go from there.
  3. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    Take a look at your coolant level?
  4. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    first i would check coolent level. iff good then get a hand held temp gauge ( infa red laser style ) has many uses. let it warm up. then check at tsat housing to see if its opening at what temp. if within 5 degress good.

    next check at both sensors for temp. one for computer use. mostly on intake by t stat. then one in head for gauge use. it might be warm but bad gauge sender lots of times. a good shop scanner will show both to cross reference them to check for bad.

    if both are within 5-10 degres of tstat temp good. next check both sides of the heater core inlet and outlet . should be with in 10 degrese of each other. if more you have a pluged heater core. vary comon these days . gm is the worst with that dex cool junk for pluging cores.

    if non of this shows the problem you have other issues. i bet this will show it vary quick. :salute:
  5. temp check

    A. Sears sells the infrared thermometers for about $80
    Check to see if the guys at your auto parts store will check with theirs.
    Or stop by your friendly body shop -- they use them too.

    B. I saw a radiator cap for sale with a built in thermometer -- hmmm

    C. May be able to hold a cooking thermometer in the radiator cap/hole
    while idling after 'warmup'.

    Or all of the ideas previously mentioned
  6. streetsurfin'

    streetsurfin' Senior Member
    Messages: 770

    Could you have put the stat in backwards? I think that the flow then might force it open and cause it to run cool. Seems I've read that somewhere, but I am not 100% positive I have it correct.
  7. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    I was told by a parts counter guy that the average of bad parts right out of the box is 1 in 10,000. Well, I have been mister 10,000 more then my share![/I]Get a candy thermometer and put the thermostat and the thermometer in a pan of water with the burner on the stove going. Watch and see if it opens near the temp it's rated at. I bet it opens real quick, well below the rating. Drop a handful of ice cubs in the water, if it does not close consider replacing it AGAIN.

    REAPER 2000 Club Member
    from 60050
    Messages: 2,230

    I would check the gauge itself.

    If anything buy one but have it on the side and plug it in.
    Watch the reading on new one.

    If is same you should be able to return it since you did not install it.

    My guess is the gauge itself is malfunctioning.
  9. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    Well he posted yesterday??

    His cooling issue must not be a priority for him....

    I dosn't matter if the gage works or not, he has no heat.

    clogged heater core or the actuator for the heater is not working.
    Low coolent level.
    no thermostat.
    Last edited: Jan 18, 2008
  10. moosey

    moosey Senior Member
    Messages: 173

    I bet it is a heater core. I have an '01 that didnt blow any hot air for the heat. Took forever to show anythin on the temp gauge. Pulled heater core and flushed system and Good to Go!
  11. mayhem

    mayhem PlowSite.com Addict
    from Peru MA
    Messages: 1,016

    Run your truck normally and then when you shut it off open the hood and feel each of the hoses to see if they're hot. If either the feed or return on the radiator is cold you probably have a bad thermostat. If both radiator hoses are good then you'r gauge is possibly got a bad sending unit...or the sending unit may be at or near your heater core and your core is plugged up. To check that just feel the two hoses that go into your firewall...if one is cod and the other is hot (which I suspect is the case) then you've got a plugged up core and you need to flush it out. With the truck cold simply pull both hoses off the firewall (make note of which one goes where) and use your garden hose to blow the crap out...make sure to flush the water into the hose outlet that was cold to the touch...that hose is the return line from the core and the crud in the core is lodged in there in the direction of the normal flow...reversing the flow will dislodge most if not all of it and blow it right out. Did this to my Silverado a couple weeks ago when we had that nice thaw...I had zero heat in the cab before...now it'll drive you out of the cab its so hot.

    If you do this and yo get crud out of your core it might be a good idea to just flush the whole system out...those contaminants got in there from somewhere so you may have a deposit built up somewhere else in the system. Best to just drain it all out, reverse flush it with the hose and then replace all the fluid...make sure to get all the water out.
  12. justme-

    justme- 2000 Club Member
    Messages: 2,138

    improper coolant mixture! too much antifreeze will keep it running cold too.